0001564590-21-006074 | 10-K | XBRL Viewer

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Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Dec. 31, 2020	Feb. 11, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Title of 12(b) Security	Common Shares, nominal value CHF 0.03
Trading Symbol	CRSP
Security Exchange Name	NASDAQ
Entity Registrant Name	CRISPR THERAPEUTICS AG
Entity Central Index Key	0001674416
Entity Tax Identification Number	00-0000000
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity File Number	001-37923
Entity Address, Address Line One	Baarerstrasse 14
Entity Address, City or Town	Zug
Entity Address, Country	CH
Entity Address, Postal Zip Code	6300
City Area Code	41 (0)41
Local Phone Number	561 32 77
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	V8
Document Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		75,428,927
Entity Public Float			$ 4.5
ICFR Auditor Attestation Flag	false
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to the 2021 Annual General Meeting of Shareholders, which the Registrant intends to file with the Securities and Exchange Commission pursuant to Regulation 14A within 120 days after the end of the Registrant’s fiscal year ended December 31, 2020, are incorporated by reference into Part III of this Report.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 1,168,620	$ 943,771
Marketable securities	521,713	0
Accounts receivable	144	99
Prepaid expenses and other current assets	26,143	43,677
Total current assets	1,716,620	987,547
Property and equipment, net	42,160	31,330
Intangible assets, net	180	235
Restricted cash	16,848	5,041
Operating lease assets	50,865	41,502
Other non-current assets	1,293	1,097
Total assets	1,827,966	1,066,752
Current liabilities:
Accounts payable	9,094	5,944
Accrued expenses	53,782	30,180
Deferred revenue, current	2,341	960
Accrued tax liabilities	10,473	583
Operating lease liabilities	11,362	8,489
Other current liabilities	7,207	10,950
Total current liabilities	94,259	57,106
Deferred revenue, non-current	11,776	11,776
Operating lease liabilities, net of current portion	50,067	44,050
Other non-current liabilities	7,630	14,395
Total liabilities	163,732	127,327
Commitments and contingencies (Note 8)
Shareholders’ equity:
Common shares, CHF 0.03 par value, 115,172,786 and 103,901,006 shares authorized at December 31, 2020 and 2019, respectively, 74,110,160 and 61,034,025 shares issued at December 31, 2020 and 2019, respectively, 73,914,844 and 60,783,799 shares outstanding at December 31, 2020 and 2019, respectively.	2,277	1,847
Treasury shares, at cost, 195,316 and 250,226 shares at December 31, 2020 and 2019, respectively	(63)	(63)
Additional paid-in capital	2,235,679	1,162,345
Accumulated deficit	(573,576)	(224,711)
Accumulated other comprehensive income (loss)	(83)	7
Total shareholders’ equity	1,664,234	939,425
Total liabilities and shareholders’ equity	$ 1,827,966	$ 1,066,752

Consolidated Balance Sheets (Parenthetical) - SFr / shares	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Common stock, par value	SFr 0.03	SFr 0.03
Common stock, shares authorized	115,172,786	103,901,006
Common stock, shares issued	74,110,160	61,034,025
Common stock, shares outstanding	73,914,844	60,783,799
Treasury stock, shares	195,316	250,226

Consolidated Statements of Operations and Comprehensive (Loss) Income - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Revenue:

Total revenue

$ 719

$ 289,590

$ 3,124

Operating expenses:

Research and development

^[1]

266,946

179,362

113,773

General and administrative

88,208

63,488

48,294

Total operating expenses

355,154

242,850

162,067

(Loss) income from operations

(354,435)

46,740

(158,943)

Other income (expense):

Loss from equity method investment

(5,467)

(4,275)

Other income (expense), net

6,379

26,033

(1,210)

Total other income (expense), net

6,379

20,566

(5,485)

Net (loss) income before income taxes

(348,056)

67,306

(164,428)

Provision for income taxes

(809)

(448)

(553)

Net (loss) income

(348,865)

66,858

(164,981)

Foreign currency translation adjustment

(22)

Unrealized loss on marketable securities

(130)

Comprehensive (loss) income

$ (348,955)

$ 66,873

$ (165,003)

Net (loss) income per common share — basic

$ (5.29)

$ 1.23

$ (3.44)

Basic weighted-average common shares outstanding

65,949,672

54,392,304

47,964,368

Net (loss) income per common share — diluted

$ (5.29)

$ 1.17

$ (3.44)

Diluted weighted-average common shares outstanding

65,949,672

56,932,798

47,964,368

Collaboration Revenue [Member]

Revenue:

Total revenue

^[2]

$ 543

$ 289,590

$ 3,124

Grant Revenue [Member]

Revenue:

Total revenue

$ 176

[1]	Including the following amounts of research and development from a related party, see Note 9
[2]	Including the following amounts of revenue from a related party, see Note 9

Consolidated Statements of Operations and Comprehensive (Loss) Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenue from related party	$ 746	$ 3,124
Research and development expense with a related party	$ 14,459	$ 23,982

Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative effect of ASC 606 adoption [Member]	ViaCyte [Member]	Common Shares [Member]	Common Shares [Member] ViaCyte [Member]	Treasury Shares [Member]	Treasury Shares [Member] ViaCyte [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] ViaCyte [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member] Cumulative effect of ASC 606 adoption [Member]	Accumulated Other Comprehensive (Loss) Income [Member]
Beginning balance at Dec. 31, 2017	$ 187,832	$ (1,148)		$ 1,240				$ 312,018		$ (125,440)	$ (1,148)	$ 14
Beginning balance (in shares) at Dec. 31, 2017				40,592,248		444,873
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201409Member
Issuance of common shares, net of issuance costs	$ 307,053			$ 311				306,742
Issuance of common shares, net of issuance costs (in shares)				9,960,526
Vesting of restricted shares	113			$ 1				112
Vesting of restricted shares (in shares)				38,761
Exercise of vested options, value	8,563			$ 26				8,537
Exercise of vested options (in shares)				946,131		(36,253)
Repurchase of treasury shares	(57)					$ (57)
Repurchase of treasury shares (in shares)				(64,952)		64,952
Issuance of shares to ViaCyte			$ 15,582		$ 6				$ 15,576
Issuance of shares to ViaCyte (in shares)					380,148		(165,636)
Stock-based compensation expense	39,260							39,260
Other comprehensive income (loss)	(22)											(22)
Net income (loss)	(164,981)									(164,981)
Ending balance at Dec. 31, 2018	392,195			$ 1,584		$ (57)		682,245		(291,569)		(8)
Ending balance (in shares) at Dec. 31, 2018				51,852,862		307,936
Issuance of common shares, net of issuance costs	414,789			$ 230				414,559
Issuance of common shares, net of issuance costs (in shares)				7,704,068		(47,297)
Vesting of restricted shares	43			$ 2				41
Vesting of restricted shares (in shares)				68,009
Exercise of vested options, value	16,001			$ 31		$ (6)		15,976
Exercise of vested options (in shares)				1,158,860		(10,413)
Stock-based compensation expense	49,524							49,524
Other comprehensive income (loss)	15											15
Net income (loss)	66,858									66,858
Ending balance at Dec. 31, 2019	939,425			$ 1,847		$ (63)		1,162,345		(224,711)		7
Ending balance (in shares) at Dec. 31, 2019				60,783,799		250,226
Issuance of common shares, net of issuance costs	973,381			$ 366				973,015
Issuance of common shares, net of issuance costs (in shares)				11,412,519
Vesting of restricted shares	7			$ 7
Vesting of restricted shares (in shares)				204,650
Exercise of vested options, value	$ 32,775			$ 57				32,718
Exercise of vested options (in shares)	1,517,735			1,482,636		(37,080)
Purchase of common stock under ESPP	$ 694							694
Purchase of common stock under ESPP (in shares)				13,410
Issuance of shares to ViaCyte	889							889
Issuance of shares to ViaCyte (in shares)				17,830		(17,830)
Stock-based compensation expense	66,018							66,018
Other comprehensive income (loss)	(90)											(90)
Net income (loss)	(348,865)									(348,865)
Ending balance at Dec. 31, 2020	$ 1,664,234			$ 2,277		$ (63)		$ 2,235,679		$ (573,576)		$ (83)
Ending balance (in shares) at Dec. 31, 2020				73,914,844		195,316

Consolidated Statements of Shareholders' Equity (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 SFr / shares	Dec. 31, 2019 SFr / shares	Dec. 31, 2018 SFr / shares
Common shares, par value \| SFr / shares				SFr 0.03	SFr 0.03
Stock Options [Member]
Issuance costs \| $	$ 1.2	$ 0.3	$ 0.4
Common Shares [Member]
Issuance costs \| $	$ 46.4	$ 25.1	$ 23.8
Common shares, par value \| SFr / shares				SFr 0.03	SFr 0.03	SFr 0.03

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net (loss) income	$ (348,865)	$ 66,858	$ (164,981)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	9,184	4,725	3,519
Equity-based compensation	66,018	44,057	34,985
Loss from equity method investment in Casebia		5,467	4,275
Non-cash expense related to ViaCyte transaction			15,582
Gain from consolidation of Casebia		(16,000)
Other income (expense), non-cash	1,857		(169)
Changes in:
Accounts receivable	(45)	(11)	2,538
Prepaid expenses and other assets	17,338	(32,618)	(3,342)
Accounts payable and accrued expenses	25,747	5,025	12,110
Deferred revenue	1,381	(45,146)	(296)
Deferred rent			(709)
Operating lease assets and liabilities	(473)	(663)
Other liabilities, net	(10,508)	24,983	249
Net cash (used in) provided by operating activities	(238,366)	56,677	(96,239)
Investing activities
Purchase of property, plant and equipment	(18,358)	(6,684)	(2,773)
Net cash and restricted cash received in connection with the acquisition of Casebia		8,009
Purchases of marketable securities	(593,998)
Maturities of marketable securities	71,186
Net cash (used in) provided by investing activities	(541,170)	1,325	(2,773)
Financing activities
Proceeds from issuance of common shares, net of issuance costs	982,289	415,019	307,053
Proceeds from exercise of options and ESPP contributions, net of issuance costs	33,863	15,964	8,938
Repurchase of treasury shares			(57)
Net cash provided by financing activities	1,016,152	430,983	315,934
Effect of exchange rate changes on cash	40	15	(22)
Increase in cash	236,656	489,000	216,900
Cash, cash equivalents and restricted cash, beginning of period	948,812	459,812	242,912
Cash, cash equivalents and restricted cash, end of period	1,185,468	948,812	459,812
Supplemental disclosure of non-cash investing and financing activities
Property and equipment purchases in accounts payable and accrued expenses	3,412	1,811	334
Equity issuance costs in accounts payable and accrued expenses	$ 9,590	$ 295	$ 375

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation to amounts within the consolidated balance sheets
Cash and cash equivalents	$ 1,168,620	$ 943,771	$ 456,649
Restricted Cash	16,848	5,041	3,163
Total	$ 1,185,468	$ 948,812	$ 459,812	$ 242,912

Organization and Operations

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Operations

1. Organization and Operations

CRISPR Therapeutics AG (“CRISPR” or the “Company”) was incorporated on October 31, 2013 in Basel, Switzerland. The Company was established to translate CRISPR/Cas9, a genome editing technology, into transformative gene-based medicines for the treatment of serious human diseases. The foundational intellectual property underlying the Company’s operations was licensed to the Company in April 2014. The Company devotes substantially all of its efforts to product research and development activities, initial market development and raising capital. The Company’s principal offices are in Zug, Switzerland and operations are in Cambridge, Massachusetts.

The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any drug product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and ability to transition from pilot-scale manufacturing to large-scale production of products.

The Company had an accumulated deficit of $573.6 million as of December 31, 2020 and has financed its operations to date from a series of preferred shares and convertible loan issuances, proceeds obtained from its initial public offering, subsequent public offerings of its common shares, as well as upfront fees and milestones received under its collaboration and joint venture arrangements. The Company will require substantial additional capital to fund its research and development and ongoing operating expenses.

As of December 31, 2020, the Company had cash, cash equivalents and marketable securities of $1,690.3 million. While the Company had net income of $66.9 million for the year ended December 31, 2019, the Company has a history of recurring losses, including a loss of $348.9 million for the year ended December 31, 2020, and expects to continue to incur losses for the foreseeable future. The Company expects its cash and cash equivalents will be sufficient to fund current planned operations for at least the next twenty-four months.

The full extent of the impact of the coronavirus pandemic on the Company’s business, operations and financial results will depend on numerous evolving factors that we may not be able to accurately predict. See Item 1A: "Risk Factors" section set forth in this Annual Report on Form 10-K for additional details. At this stage, the impact on the Company’s results has not been significant.

Summary of Significant Accounting Policies and Basis of Presentation

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies and Basis of Presentation

2. Summary of Significant Accounting Policies and Basis of Presentation

Basis of Presentation and Use of Estimates

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America, or GAAP, and include the accounts of the Company and its wholly-owned subsidiaries as of December 31, 2020. All intercompany accounts and transactions have been eliminated. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification, or ASC, and Accounting Standards Updates, or ASUs, of the Financial Accounting Standards Board.

Prior to December 13, 2019, the Company accounted for its 50% investment in Casebia Therapeutics, Limited Liability Partnership, or Casebia, under the equity method. As described in Note 9, on December 13, 2019, Casebia became a wholly-owned subsidiary and, as a result, the Company consolidated Casebia’s financial results from that date forward.

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, revenue recognition, equity-based compensation expense and reported amounts of research and development expenses during the period. Significant estimates in these consolidated financial statements have been made in connection with revenue recognition and equity-based compensation expense. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.

Certain items in the prior year’s consolidated financial statements have been reclassified to conform to the current presentation. As a result, no subtotals in the prior year consolidated financial statements were impacted.

Segment Information

The Company and the Company’s chief operating decision maker, namely, the chief executive officer, view the Company’s operations and manage its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology.

Foreign Currency Translation and Transactions

The majority of the Company’s operations occur in entities that have the U.S. dollar as their functional currency. Non-U.S. dollar denominated functional currency subsidiaries have assets and liabilities translated into U.S. dollars at rates of exchange in effect at the end of the year. Revenue and expense amounts are translated using the average exchange rates for the period. Net unrealized gains and losses resulting from foreign currency translation are included in “Accumulated other comprehensive (loss) income.” Net foreign currency exchange transaction gains or losses are included in “Other income (expense), net” on the Company’s consolidated statement of operations, the impact of which is not significant.

Cash and Cash Equivalents

The Company considers all highly liquid investments with maturities of three months or less from the purchase date to be cash equivalents. As of December 31, 2020 and 2019, the Company had $1,168.6 million and $943.8 million in cash equivalents, respectively.

Restricted Cash

As of December 31, 2020 and 2019, the Company had $16.8 million and $5.0 million, respectively, in restricted cash representing letters of credit securing the Company’s obligations under certain leased facilities, as well as certain credit card arrangements. The letters of credit are secured by cash held in a restricted depository account and recorded in restricted cash in the accompanying consolidated balance sheet as of December 31, 2020.

Marketable Securities

As of December 31, 2020 and 2019, the Company had $521.7 million and $0.0 million, respectively in marketable securities. The Company’s investment strategy is focused on capital preservation. The Company invests in instruments that meet the credit quality standards outlined in the Company’s investment policy. The Company classifies marketable securities with a remaining maturity, when purchased, of greater than three months as available-for-sale. The Company classifies marketable securities available to fund current operations as current assets on its consolidated balance sheets. Marketable securities are classified as long-term assets on the consolidated balance sheets if (i) they have been in an unrealized loss position for longer than one year or (ii) the Company has the ability and intent to hold them (a) until the carrying value is recovered and (b) such holding period may be longer than one year.

Marketable securities classified as Level 2 within the valuation hierarchy generally consist of U.S. treasury securities and government agency securities, corporate bonds, and commercial paper. Debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive (loss) income as a component of stockholders’ equity until realized. Any premium arising at purchase is amortized to interest expense over the period of the earliest call date, and any discount arising at purchase is accreted to interest income over the life of the instrument. Realized gains and losses on debt securities are determined using the specific identification method and are included in other income (expense), net.

Effective January 1, 2020, the Company adopted ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Statements, or ASC 326. As the Company did not hold available-for-sale debt securities upon adoption, no related transition provisions were applicable to the Company upon adoption.

The Company assesses its available-for-sale debt securities under the available-for-sale debt security impairment model in ASC 326 as of each reporting date in order to determine if a portion of any decline in fair value below carrying value recognized on its available-for-sale debt securities is the result of a credit loss. The Company records credit losses in the consolidated statements of operations and comprehensive loss as credit loss expense within other expense, net, which is limited to the difference between the fair value and the amortized cost of the security. To date, the Company has not recorded any credit losses on its available-for-sale debt securities.

Other Receivables

Amounts due from collaboration partners where an arrangement is accounted for under ASC 808, Collaborative Arrangements, or ASC 808, are considered other receivables and are included within prepaid and other current assets in the consolidated balance sheet. Other receivables consisted of $10.7 million and $4.1 million as of December 31, 2020 and 2019, respectively and are due from Vertex Pharmaceuticals Incorporated and certain of its subsidiaries, or Vertex. Other receivables are recorded at invoiced amounts due under the Vertex collaboration agreement, as described further in Note 9. Vertex is a creditworthy entity that maintains an ongoing relationship with the Company and as such, the Company does not have an allowance for estimated credit losses recorded related to these other receivables.

Concentrations of Credit Risk and Off-balance Sheet Risk

Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash, cash equivalents and marketable securities. The Company’s cash is held in accounts with financial institutions that management believes are creditworthy. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no financial instruments with off-balance sheet risk of loss.

Fair Value of Financial Instruments

The Company has certain financial assets and liabilities recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements:

Level 1 —

Quoted prices in active markets that are accessible at the market date for identical unrestricted assets or liabilities.

Level 2 —

Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs for which all significant inputs are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 —

Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Items measured at fair value on a recurring basis include marketable securities (see Note 3, Marketable Securities, and Note 4, Fair Value Measurement). The carrying amount of accounts receivable, other receivables, accounts payable and accrued expenses as reported on the consolidated balance sheets as of December 31, 2020 and 2019, approximate fair value, due to the short-term duration of these instruments.

Property and Equipment

Property and equipment are recorded at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows:

Asset		Estimated useful life
Computer equipment		3 years
Furniture, fixtures and other		5 years
Laboratory equipment		5 years
Leasehold improvements		Shorter of useful life or remaining lease term

Impairment of Long-lived Assets

The Company reviews long-lived assets when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparison of the book values of the assets to future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets.

Revenue Recognition

Effective January 1, 2018, the Company adopted ASC Topic 606, Revenue from Contracts with Customers, or ASC 606, using the modified retrospective transition method by recognizing the cumulative effect of initially applying ASC 606 as an adjustment to the opening balance of equity at January 1, 2018. The adoption of this guidance did not have a significant impact on our consolidated financial statements.

In connection with adopting ASC 606, the Company elected a practical expedient and applied ASC 606 only to contracts that were not completed at the date of initial application. In addition, the Company applied the practical expedient in ASC 606-10-65-1 in identifying the satisfied and unsatisfied performance obligations, determining the transaction price and allocating the transaction price under the practical expedient in ASC 606.

ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases and collaboration arrangements. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps:

1) Identify the contract with the customer

A contract with a customer exists when (i) the Company enters into an enforceable contract with a customer that defines each party’s rights regarding the goods or services to be transferred and identifies the related payment terms, (ii) the contract has commercial substance and (iii) the Company determines that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration.

2) Identify the performance obligations in the contract

Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct, whereby the customer can benefit from the good or service either on its own or together with other available resources, and are distinct in the context of the contract, whereby the transfer of the good or service is separately identifiable from other promises in the contract. To the extent a contract includes multiple promised goods and services, the Company must apply judgment to determine whether promised goods and services are capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation.

3) Determine the transaction price

The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration such as research, development, regulatory and commercial milestones, the Company determines if it is probable that it will receive such amounts and there is no risk of a significant revenue reversal. When the Company cannot conclude that receipt of such amounts is probable, the Company constrains the related variable consideration resulting in its exclusion from transaction consideration. In determining the portion of the transaction consideration to be constrained, the Company considers the probability and uncertainty that the related research, developmental, regulatory and commercial milestones will be achieved given the nature of research and clinical development and the stage of the underlying programs. This assessment is performed at each reporting period. In making this evaluation, the Company considers both internal and external information available, including information from industry publications and other relevant factors. Changes to the constraint of variable consideration can have a material effect on the amount of revenue recognized in the period.

4) Allocate the transaction consideration to performance obligations in the contract

If the contract contains a single performance obligation, the entire transaction consideration is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction consideration to each performance obligation on a relative standalone selling price basis unless the transaction consideration is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices. In determining these estimated standalone selling prices, the Company makes a number of significant judgements including, for licenses, management’s assumptions regarding probability weighted projected discounted cash flows for each of the collaboration development programs. The estimated standalone selling prices are sensitive to changes in assumptions, such as probabilities of scientific success, discount rate and certain assumptions that form the basis of forecasted cash flows. In developing these assumptions, management considers both internal and external information available, including information from other guideline companies within the same industry and other relevant factors. Changes to these assumptions can have a material effect on the allocation of the transaction consideration to performance obligations, as well as the amount and timing of revenue recognized.

5) Recognize revenue when or as the Company satisfies a performance obligation

The Company satisfies performance obligations over time or at a point in time, depending on the nature of the performance obligation. Revenue is recognized over time if the customer simultaneously receives and consumes the benefits provided by the entity’s performance, the entity’s performance creates or enhances an asset that the customer controls as the asset is created or enhanced, or the entity’s performance does not create an asset with an alternative use to the entity and the entity has an enforceable right to payment for performance completed to date. If the entity does not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring the control of a promised good or service to a customer.

Contract Balances

The Company recognizes a contract asset when the Company transfers goods or services to a customer before the customer pays consideration or before payment is due, excluding any amounts presented as an account or other receivable. A contract asset is an entity’s right to consideration in exchange for goods or services that the entity has transferred to a customer. The contract liabilities, or deferred revenue, primarily relate to contracts where we have received payment, but we have not yet satisfied the related performance obligations. The Company recorded contract assets of $0.3 million and $25.7 million as of December 31, 2020 and 2019, respectively. Contract liabilities recorded as deferred revenue as of December 31, 2020 and 2019 are$12.2 million and $12.7 million, respectively. The change in contract assets and contract liabilities recorded as deferred revenue is related to the collaboration agreement with Vertex described in Note 9.

Grant Revenue

The Company has contracts with certain not-for-profit organizations. The Company records upfront payments related to these contracts as deferred revenue and recognizes revenue as services are performed. Revenue and related expenses are presented gross in the consolidated statements of operations, as the Company is the primary obligor under the arrangements relative to the research and development services the Company performs as lead technical expert. Deferred revenue related to these contracts as of December 31, 2020 was $1.9 million. There was no deferred revenue related to these contracts as of December 31, 2019. Grant revenue under these contracts was not material for the periods presented in the consolidated statement of operations.

Collaboration Arrangements

The Company records the elements of its collaboration agreements that represent joint operating activities in accordance with ASC 808, Collaborative arrangements, or ASC 808. Accordingly, the elements of the collaboration agreements that represent activities in which both parties are active participants and to which both parties are exposed to the significant risks and rewards that are dependent on the commercial success of the activities, are recorded as collaborative arrangements.

The Company evaluates the proper presentation of the commercial activities and the proﬁt and loss sharing associated with the collaboration agreements. ASC 808 states that when payments between parties in a collaborative arrangement are not within the scope of other authoritative accounting literature, the income statement classification should be based on the nature of the arrangement, the nature of its business operations and the contractual terms of the arrangement. To the extent that these payments are not within the scope of other authoritative accounting literature, the income statement classification for the payments shall be based on an analogy to authoritative accounting literature or if there is no appropriate analogy, a reasonable, rational and consistently applied accounting policy election.

Research and Development Expenses

Research and development costs are charged to expense as costs are incurred in performing research and development activities, including salaries and benefits, facilities costs, overhead costs, clinical study and related clinical manufacturing costs, license and milestone fees, contract services and other related costs. Research and development costs, including up-front fees and milestones paid to collaborators, are also expensed as incurred. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense. The Company accrues costs for clinical trial activities based upon estimates of the services received and related expenses incurred that have yet to be invoiced by the contract research organizations, clinical study sites, laboratories, consultants or other clinical trial vendors that perform the activities. The Company recognizes the reimbursement associated with collaborative activities to its collaborative partners as research and development expense in the period the services are provided.

Leases

Effective January 1, 2019, the Company adopted ASC 842, Leases, or ASC 842, using the required modified retrospective approach and utilizing the effective date as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840, Leases, or ASC 840.

The Company chose to apply the transition provisions as of the period of adoption. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which, among other things, allowed the Company to carry forward the historical lease classification. In addition, the Company elected the practical expedient not to apply the recognition requirements in the lease standard to short-term leases (a lease that at commencement date has a lease term of 12 months or less and does not contain a purchase option that it is reasonably certain to exercise) and the practical expedient that permits lessees to make an accounting policy election (by class of underlying asset) to account for each separate lease component of a contract and its associated non-lease components as a single lease component. The adoption of the new standard resulted in the recording net lease assets and lease liabilities of $26.1 million and $37.6 million, respectively, as of January 1, 2019. The difference between the additional lease assets and lease liabilities is primarily due to the change in classification of lease incentives from liabilities to a reduction in the Company’s net lease assets. The standard had no impact on the Company’s net loss or cash flows.

The adoption of ASC 842 had the following impact on the financial statements:

	January 1, 2019 Prior to ASC 842 Adoption		ASC 842 Adjustment			January 1, 2019 As Adjusted
Consolidated Balance Sheet Data (in thousands):
Prepaid expenses and other current assets⁽¹⁾	$	9,658	$	(553	)	$	9,105
Operating lease assets⁽²⁾	$	—	$	26,087		$	26,087
Deferred rent⁽³⁾⁽⁴⁾	$	1,026	$	(1,026	)	$	—
Deferred rent non-current⁽³⁾	$	11,052	$	(11,052	)	$	—
Operating lease liabilities⁽⁵⁾	$	—	$	4,930		$	4,930
Non-current operating lease liabilities⁽⁵⁾	$	—	$	32,682		$	32,682

(1) Represents reclassification of prepaid rent to operating lease assets.
(2) Represents capitalization of operating lease assets and reclassification of equipment licenses from prepaid expenses to operating lease assets, offset by reclassification of deferred rent to operating lease assets.
(3) Represents reclassification of deferred rent and tenant incentives to operating lease assets.
(4) As of December 31, 2018, the deferred rent balance was $1,202, which included $176 of sublease income received prior to year-end but not due until January 1, 2019.
(5) Represents recognition of operating lease liabilities.

At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and short-term and long-term lease liabilities, as applicable. The Company does not have financing leases.

Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. Prospectively, the Company will adjust the right-of-use assets for straight-line rent expense or any incentives received and remeasure the lease liability at the net present value using the same incremental borrowing rate that was in effect as of the lease commencement or transition date.

The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty of renewal.

Assumptions made by the Company at the commencement date are re-evaluated upon occurrence of certain events, including a lease modification. A lease modification results in a separate contract when the modification grants the lessee an additional right of

use not included in the original lease and when lease payments increase commensurate with the standalone price for the additional right of use. When a lease modification results in a separate contract, it is accounted for in the same manner as a new lease.

Equity Based Compensation Expense

The Company’s share-based compensation programs grant awards that have included stock options, restricted stock units and restricted stock awards. Grants are awarded to employees and non-employees, including directors.

The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation, or ASC 718. ASC 718 requires all stock-based payments to employees and non-employee directors, including grants of employee stock options and restricted stock units and modifications to existing stock options, to be recognized in the consolidated statements of operations and comprehensive income (loss) based on their fair values. The Company uses the Black-Scholes option pricing model to determine the fair value of options granted.

The Company accounts for forfeitures as they occur instead of estimating forfeitures at the time of grant and revising those estimates in subsequent periods if actual forfeitures differ from its estimates. Stock-based compensation expense recognized in the financial statements is based on awards for which performance or service conditions are expected to be satisfied.

Prior to the adoption of ASU No. 2018-07, Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, or ASU 2018-07, on July 1, 2018, the measurement date for non-employee awards was generally the date the services are completed, resulting in financial reporting period adjustments to stock-based compensation during the vesting terms for changes in the fair value of the awards. After adoption of ASU 2018-07, the measurement date for non-employee awards is the date of grant without changes in the fair value of the award.

The Company’s stock-based awards are subject to service or performance-based vesting conditions. Compensation expense related to awards to employees, directors and non-employees with service-based vesting conditions is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term. Compensation expense related to awards to employees and non-employees with performance-based vesting conditions is recognized based on the grant date fair value over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable.

The Company expenses restricted stock unit awards to employees based on the fair value of the award on a straight-line basis over the associated service period of the award.

The Company estimates the fair value of its option awards to employees, directors and non-employees using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including (i) the expected stock price volatility, (ii) the calculation of expected term of the award, (iii) the risk-free interest rate and (iv) expected dividends. Due to the lack of complete company-specific historical and implied volatility data for the full expected term of the stock-based awards, the Company bases its estimate of expected volatility on a representative group of publicly traded companies in addition to its own volatility data. For these analyses, the Company selected companies with comparable characteristics to its own, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected life of the stock-based awards. The Company computes historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. The Company has estimated the expected term of its employee stock options using the “simplified” method, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option, due to its lack of sufficient historical data. The risk-free interest rates for periods within the expected term of the option are based on the U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid, and does not expect to pay, dividends in the foreseeable future.

Patent Costs

Costs to secure and prosecute patent applications and other legal costs related to the protection of the Company’s intellectual property are expensed as incurred and are classified as general and administrative expenses in the Company’s consolidated statements of operations.

Income Taxes

Income taxes are recorded in accordance with ASC Topic 740, Income Taxes, or ASC 740, which provides for deferred taxes using an asset and liability approach. Under this method, deferred tax assets and liabilities are determined based on the difference

between the financial reporting and tax reporting basis of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. Valuation allowances are provided if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has evaluated available evidence and concluded that the Company may not realize all the benefit of its deferred tax assets; therefore, a valuation allowance has been established for the amount of the deferred tax assets that the Company does not believe is more likely than not to be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2020, and 2019, the Company does not have any significant uncertain tax positions. The Company’s practice is to recognize interest and/or penalties related to income tax matters in income tax expense. See Note 14 for further details.

Comprehensive (Loss) Income

Comprehensive (loss) income consists of net income or loss and other comprehensive (loss) income. Other comprehensive (loss) income consists of foreign currency translation adjustments and unrealized losses on marketable securities.

Variable Interest Entities

The Company reviews each legal entity formed by parties related to the Company to determine whether or not the Company has a variable interest in the entity and whether or not the entity would meet the definition of a variable interest entity, or VIE, in accordance with ASC Topic 810, Consolidation, or ASC 810. If the entity is a VIE, the Company assesses whether or not the Company is the primary beneficiary of that VIE based on a number of factors, including (i) which party has the power to direct the activities that most significantly affect the VIE’s economic performance, (ii) the parties’ contractual rights and responsibilities pursuant to any contractual agreements and (iii) which party has the obligation to absorb losses or the right to receive benefits from the VIE. If the Company determines it is the primary beneficiary of a VIE, the Company consolidates the financial statements of the VIE into the Company’s consolidated financial statements at the time that determination is made. The Company evaluates whether it continues to be the primary beneficiary of any consolidated VIEs on a quarterly basis. If the Company were to determine that it is no longer the primary beneficiary of a consolidated VIE, or no longer has a variable interest in the VIE, it would deconsolidate the VIE in the period that the determination is made.

If the Company determines it is the primary beneficiary of a VIE that meets the definition of a business, the Company measures the assets, liabilities and noncontrolling interests of the newly consolidated entity at fair value in accordance with ASC Topic 805, Business Combinations, or ASC 805, at the date the reporting entity first becomes the primary beneficiary.

In February 2016, Casebia, was formed in the United Kingdom. In March 2016, upon consummation of the joint venture (“JV”), Bayer Healthcare LLC and certain of its affiliates (“Bayer”) and the Company each received a 50% equity interest in the entity in exchange for their contributions to the entity. The Company determined that Casebia was considered a VIE and concluded that it is not the primary beneficiary of the VIE. As such, the Company has not historically consolidated Casebia’s results into the consolidated financial statements.

As described in Note 9, on December 13, 2019, Casebia became a fully-owned subsidiary and, as a result, the Company consolidated Casebia’s financial results accordingly from that point forward.

Net (Loss) Income Per Share Attributable to Common Shareholders

Basic net (loss) income per share is calculated by dividing net (loss) income attributable to common shareholders by the weighted-average number of common shares outstanding during the period. Diluted net income per share is calculated by dividing the net income attributable to common shareholders by the weighted-average number of common equivalent shares outstanding for the period, including any dilutive effect from outstanding stock options and restricted stock units using the treasury stock method. See Note 12 for further details.

New Accounting Pronouncements – Recently Adopted

From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that the Company adopts as of the specified effective date. Unless otherwise discussed below, the Company does not believe that the adoption of recently issued standards have or may have a material impact on its consolidated financial statements and disclosures.

Credit Losses

In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Statements, or ASC 326. On January 1, 2020, the Company adopted ASC 326. The new standard requires that expected credit losses relating to financial assets measured on an amortized cost basis and available-for-sale debt securities be recorded through an allowance for credit losses. It also limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and also requires the reversal of previously recognized credit losses if fair value increases. The targeted transition relief standard allows filers an option to irrevocably elect the fair value option of ASC 825-10, Financial Instruments-Overall, applied on an instrument-by-instrument basis for eligible instruments. The Company adopted ASC 326 using the modified retrospective method for all financial assets measured at amortized cost. The adoption of ASC 326 did not have a material impact on the Company’s financial position or results of operations upon adoption.

New Accounting Pronouncements – Not Yet Adopted

ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, or ASU 2019-12, which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard will be effective beginning January 1, 2021. The Company is currently evaluating the potential impact ASU 2019-12 may have on its financial position and results of operations upon adoption.

Marketable Securities

12 Months Ended

Dec. 31, 2020

Investments Debt And Equity Securities [Abstract]

Marketable Securities

3. Marketable Securities

A summary of the Company’s cash equivalents and marketable securities, which are recorded at fair value (and excludes $395.1 million of cash at December 31, 2020) is shown below (in thousands):

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	$	742,958	$	—	$	—		$	742,958
Corporate debt securities		2,526		1		(24	)		2,503
Certificates of deposit		12,527		—		—			12,527
Commercial paper		15,549		—		—			15,549
Total cash equivalents		773,560		1		(24	)		773,537
Marketable securities:
U.S. Treasury securities		47,976		3		—			47,979
Corporate debt securities		324,569		43		(156	)		324,456
Certificates of deposit		25,162		—		—			25,162
Government-sponsored enterprise securities		33,738		5		(2	)		33,741
Commercial paper		90,375		—		—			90,375
Total marketable securities		521,820		51		(158	)		521,713
Total cash equivalents and marketable securities	$	1,295,380	$	52	$	(182	)	$	1,295,250

The amortized cost of all cash equivalents as of December 31, 2019 approximated fair value and the Company did not hold any marketable securities as of December 31, 2019.

As of December 31, 2020, the aggregate fair value of marketable securities that were in an unrealized loss position for less than twelve months was $280.3 million. As of December 31, 2020, no marketable securities were in an unrealized loss position for more than twelve months. The Company has recorded a net unrealized loss of $0.1 million during the year ended December 31, 2020 related to its marketable securities, which is included in comprehensive (loss) income on the consolidated statements of operations and comprehensive (loss) income.

The Company determined that there was no material change in the credit risk of the above investments. As such, an allowance for credit losses was not recognized. As of December 31, 2020, the Company does not intend to sell such securities and it is not more likely than not that the Company will be required to sell the securities before recovery of their amortized cost bases. No marketable securities held as of December 31, 2020 had remaining maturities greater than two years.

Fair Value Measurement

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurement

4. Fair Value Measurement

The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the fair value hierarchy classification of such fair values as of December 31, 2020 and 2019 (in thousands):

	Fair Value Measurements at
	December 31, 2020
	Total		Level 1		Level 2		Level 3
Cash and cash equivalents:
Cash	$	395,083	$	395,083	$	—	$	—
Money market funds		742,958		742,958		—		—
Corporate debt securities		2,503		—		2,503		—
Certificates of deposit		12,527		—		12,527		—
Commercial paper		15,549		—		15,549		—
Marketable securities:
U.S. Treasury securities		47,979		—		47,979		—
Corporate debt securities		324,456		—		324,456		—
Certificates of deposit		25,162		—		25,162		—
Government-sponsored enterprise securities		33,741		—		33,741		—
Commercial paper		90,375		—		90,375		—
Other non-current assets		600		—		—		600
Total	$	1,690,933	$	1,138,041	$	552,292	$	600

	Fair Value Measurements at
	December 31, 2019
	Total		Level 1		Level 2		Level 3
Cash and cash equivalents:
Cash	$	13,998	$	13,998		—		—
Money market funds		929,773		929,773		—		—
Other non-current assets		600		—		—		600
Total	$	944,371	$	943,771	$	—	$	600

Marketable securities classified as Level 2 within the valuation hierarchy generally consist of U.S. treasury securities and government agency securities, corporate bonds, and commercial paper. The Company estimates the fair values of these marketable securities by taking into consideration valuations obtained from third-party pricing sources.

The Company holds equity securities classified as Level 3 which are not material to the Company’s financial position.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property and Equipment, net

12 Months Ended

Dec. 31, 2020

Property Plant And Equipment [Abstract]

Property and Equipment, net

5. Property and Equipment, net

Property and equipment, net, consists of the following (in thousands):

	As of December 31,
	2020			2019
Computer equipment	$	727		$	727
Furniture, fixtures, and other		3,416			3,215
Laboratory equipment		25,353			16,640
Leasehold improvements		25,473			21,400
Construction work in process		8,366			1,394
Total property and equipment, gross		63,335			43,376
Accumulated Depreciation		(21,175	)		(12,046	)
Total property and equipment, net	$	42,160		$	31,330

Depreciation expense for the year ended December 31, 2020, 2019, and 2018 was $9.1 million, $4.7 million, and $3.5 million, respectively.

Accrued Expenses

12 Months Ended

Dec. 31, 2020

Payables And Accruals [Abstract]

Accrued Expenses

6. Accrued Expenses

Accrued expenses consist of the following (in thousands):

	As of December 31,
	2020		2019
Payroll and employee-related costs	$	22,402	$	15,229
Research costs		21,684		9,434
Licensing fees		1,401		750
Professional fees		1,670		2,040
Intellectual property costs		3,625		2,311
Accrued property and equipment		2,835		407
Other		165		9
Total	$	53,782	$	30,180

Leases

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Leases

7. Leases

In June 2015, the Company entered into a lease agreement for the lease of research facility space in Cambridge, Massachusetts, with a commencement date of November 15, 2015, or the 2015 Lease. The lease was subsequently amended in both 2017 and 2020 and now expires in September 2022 with no further option to extend. The 2015 Lease contains escalating rent clauses, which require higher rent payments in future years. With the adoption of ASC 842 in January 2019, the Company recorded a right-of-use asset and corresponding lease liability.

In May 2016, the Company entered into a sublease agreement for its primary office and research facility in Cambridge, Massachusetts, with a commencement date of December 23, 2016, or the 2016 Sublease. The sublease expires in December 2026, and the Company has an option to extend the term of the sublease for an additional five-year period if, at the time of expiration of the initial term, the sublessor does not intend to utilize the space for itself or its affiliates. The 2016 Sublease contains escalating rent clauses, which require higher rent payments in future years. With the adoption of ASC 842 in January 2019, the Company recorded a right-of-use asset and corresponding lease liability. The right-of-use asset and corresponding lease liability does not include the additional five-year period under the renewal option as the Company is not reasonably certain to exercise that option.

In May 2019, the Company entered into a lease agreement for office facility space in Cambridge, Massachusetts, with a commencement date of June 1, 2019, or the 2019 Lease. The lease expires in November 2026, and the Company has an option to extend the term of the lease for an additional five-year period based on certain conditions within the Company’s control. The 2019 Lease contains escalating rent clauses which require higher rent payments in future years. At lease commencement, the Company recorded a right-of-use asset and corresponding lease liability. The right-of-use asset and corresponding lease liability does not include the additional five-year period under the renewal option as the Company is not reasonably certain to exercise that option.

In December 2019, Casebia became a wholly-owned subsidiary of the Company. In connection therewith, Casebia assigned its sublease for an office and research facility in Cambridge, Massachusetts, or the 2019 Sublease, to the Company. The sublease expires in March 2024 and the Company has an option to extend the term of the sublease for an additional five-year period if, at the time of expiration of the initial term, the sublessor does not intend to utilize the space for itself or its affiliates. The 2019 Sublease contains escalating rent clauses which require higher rent payments in future years. The Company recorded a right-of-use asset and corresponding lease liability. The right-of-use asset and corresponding lease liability does not include the additional five-year period under the renewal option as the Company is not reasonably certain to exercise that option.

In May 2020, the Company entered into a lease agreement for a cell therapy manufacturing facility in Framingham, Massachusetts, or the Framingham Lease, for clinical and commercial production of the Company’s investigational cell therapy product candidates. The lease expires in March 2036 and the Company has an option to extend the term of the lease for two additional seven-year periods. The lease commenced in the fourth quarter of 2020, and at lease commencement, the Company recorded a right-of-use asset and corresponding lease liability. The right-of-use asset and corresponding lease liability does not include the additional seven-year periods under the renewal option as the Company is not reasonably certain to exercise that option.

In July 2020, the Company entered into a lease agreement for an office and laboratory facility in Boston, Massachusetts, or the 2020 Boston Lease. The 2020 Boston Lease is expected to commence in the first half of 2022. In connection therewith, the Company has committed to making at least $292.5 million in rental payments over a lease term of 152 months. The Company is also obligated to make certain future payments related to the construction of leasehold improvements.

In addition, the Company rents certain office space in Zug, Switzerland, on a short-term basis for which a right-of-use asset and liability are not recorded, in accordance with the practical expedient elected.

The Company has embedded leases in certain research and license agreements for which the Company has recorded a right of use asset and liability. These arrangements are not significant in comparison to the Company’s total operating lease assets and liabilities. In addition, the Company has identified certain short-term leases embedded within its manufacturing contracts which are not recorded on the Company’s balance sheet in accordance with the practical expedient elected.

The Company identified and assessed the following estimates in recognizing the right-of-use asset and corresponding liability:

•

Expected lease term: The expected lease term for those leases commencing prior to January 1, 2019 did not change with the adoption of ASC 842. The expected lease term for leases commencing after the adoption of ASC 842 includes noncancelable lease periods and, when applicable, periods covered by an option to extend the lease if the Company is reasonably certain to exercise that option, as well as periods covered by an option to terminate the lease if the Company is reasonably certain not to exercise that option.

•

Incremental borrowing rate: As the discount rates in the Company’s leases are not implicit, the Company estimated the incremental borrowing rate based on the rate of interest the Company would have to pay to borrow a similar amount on a collateralized basis over a similar term.

The following table summarizes the lease assets and liabilities as of December 31, 2020 and 2019 (in thousands):

	As of December 31,
	2020		2019
Assets
Operating lease assets	$	50,865	$	41,502
Total lease assets		50,865		41,502
Liabilities
Current
Operating lease liabilities		11,362		8,489
Non-current
Operating lease liabilities, net of current portion		50,067		44,050
Total lease liabilities	$	61,429	$	52,539

The following table summarizes operating lease costs included in research and development and general and administrative expense, as well as sublease income for the twelve months ended December 31, 2020 and 2019 (in thousands):

	Years Ended December 31,
	2020			2019
Operating lease costs	$	14,342		$	8,067
Short-term lease costs		7,339			4,554
Variable lease costs		6,368			4,282
Sublease income		(587	)		(525	)
Net lease cost	$	27,462		$	16,378

The following table summarizes the maturity of undiscounted payments due under lease liabilities and the present value of those liabilities as of December 31, 2020 (in thousands):

	Total
2021	$	17,020
2022		13,815
2023		12,650
2024		10,761
2025		10,265
Thereafter		37,206
Total	$	101,717
Present value adjustment		(40,288	)
Present value of lease liabilities	$	61,429

The following table summarizes the lease term and discount rate as of December 31, 2020 and 2019:

	As of December 31,
	2020			2019
Weighted-average remaining lease term (years)
Operating leases		9.1			6.0
Weighted-average discount rate
Operating leases		9.3	%		9.9	%

The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the year ended December 31, 2020 and 2019 (in thousands):

	Years Ended December 31,
	2020			2019
Cash paid for amounts included in measurement of lease liabilities:
Operating cash flows used in operating leases	$	(13,161	)	$	(8,420	)
Operating lease non-cash items:
Right-of-use assets increased through lease modifications and reassessments		3,169			826
Right-of-use assets obtained in exchange for operating lease liabilities		13,956			18,088

In November 2019, the Company, together with one of its partners, based on foreign exchange rates as of December 31, 2020, committed to making $3.8 million in annual rental payments to a clinical manufacturing organization under a lease arrangement for a five-year period following commencement of the lease arrangement. The lease arrangement is expected to commence in the first quarter of 2021 and all payments will be split equally between the Company and its partner.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

8. Commitments and Contingencies

Intellectual Property Agreements

Patent Assignment Agreement

In November 2014, the Company entered into a patent assignment agreement with Dr. Emmanuelle Charpentier, Dr. Ines Fonfara, and Vienna (collectively, the “Assignors”), pursuant to which the Company was assigned all rights, title and interest in and to certain patent rights claimed in the U.S. Patent Application No.61/905,835. As a result, the Assignors are entitled to receive certain low single digit clinical milestone payments and low single digit royalties based on annual net sales of licensed products and licensed services by the Company, its affiliates and sublicensees.

Charpentier License Agreements

In April 2014, the Company entered into certain technology license agreements with Dr. Charpentier pursuant to which the Company licensed certain intellectual property rights under joint ownership from Dr. Charpentier to develop and commercialize products for the treatment or prevention of human diseases. In connection therewith, Dr. Charpentier is entitled to receive nominal clinical milestone payments, low single digit percentage of sublicensing payments received under any sublicense agreement with a third party, and low single-digit percentage royalties based on annual net sales of licensed products and services by the Company and its affiliates and sublicensees.

During the years ended December 31, 2020, 2019 and 2018, the Company paid an immaterial amount of fees to Dr. Charpentier, which were recorded as research and development expense.

Research, Manufacturing and License Agreements

The Company has engaged several research institutions and companies to identify new delivery strategies and applications of the gene-editing technology. The Company is also a party to a number of research license agreements which require significant upfront payments and may require future royalty payments and potential milestone payments from time to time. In addition, the Company is also a party to intellectual property agreements, which require maintenance and milestone payments from time to time. Further, the Company is a party to a number of manufacturing agreements that require upfront payments for the future performance of services.

In association with these agreements, on a product by product basis, the counterparties are eligible to receive up to low eight-digit potential payments upon specified research, development and regulatory milestones. In addition, on a product by product basis, the counterparties are eligible to receive potential commercial milestone payments based on specified annual sales thresholds. The potential payments are low-single digit percentages of the specified annual sales thresholds. The counterparties are also eligible to receive low single-digit royalties on future net sales.

Under certain circumstances and if certain contingent future events occur, Vertex is eligible to receive up to $395.0 million in potential specified research, development, regulatory and commercial milestones and tiered single-digit royalties on future net sales. Refer to Note 9 for further discussion on the Company’s arrangements with Vertex.

Other Matters

On December 15, 2016, the Company entered into a Consent to Assignments, Licensing and Common Ownership and Invention Management Agreement (the “Invention Management Agreement”) with UC, Vienna, Dr. Charpentier, Intellia Therapeutics, Inc. Caribou Biosciences, Inc., ERS Genomics Ltd. and one of the Company’s subsidiaries. Under the Invention Management Agreement, the Company is obligated to share costs related to patent maintenance, defense and prosecution. For the years ended December 31, 2020, 2019 and 2018, the Company incurred $4.5 million, $2.9 million and $2.4 million, respectively, in shared costs. The Company recorded accrued legal costs from the cost sharing of $2.5 million and $1.5 million as of December 31, 2020 and December 31, 2019, respectively. The Company is unable to predict the outcome of these matters and is unable to make a meaningful estimate of the amount or range of loss, if any, that could result from an unfavorable outcome.

Litigation

In the ordinary course of business, the Company is from time to time involved in lawsuits, investigations, proceedings and threats of litigation related to, among other things, the Company’s intellectual property estate (including certain in-licensed intellectual property), commercial arrangements and other matters. Such proceedings may include quasi-litigation, inter partes administrative proceedings in the U.S. Patent and Trademark Office and the European Patent Office involving the Company’s intellectual property estate including certain in-licensed intellectual property. The outcome of any of the foregoing, regardless of the merits, is inherently uncertain. In addition, litigation and related matters are costly and may divert the attention of Company’s management and other resources that would otherwise be engaged in other activities. If the Company is unable to prevail in any such proceedings, the Company’s business, results of operations, liquidity and financial condition could be adversely affected.

Significant Contracts

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Significant Contracts

9. Significant Contracts

Agreements with Vertex Pharmaceuticals Incorporated and certain of its subsidiaries

Summary

On October 26, 2015, the Company entered into a strategic collaboration, option and license agreement, or the 2015 Collaboration Agreement, with Vertex. The 2015 Collaboration Agreement is focused on the use of the Company’s CRISPR/Cas9 gene-editing technology to discover and develop potential new treatments aimed at the underlying genetic causes of human disease.

On December 12, 2017, the Company and Vertex entered into Amendment No. 1 to the 2015 Collaboration Agreement, or Amendment No. 1, and the Joint Development Agreement, or the JDA. Amendment No. 1, among other things, modified certain definitions and provisions of the 2015 Collaboration Agreement to make them consistent with the JDA and clarified how many options are exercised (or deemed exercised) in connection with certain targets specified under the 2015 Collaboration Agreement. Amendment No. 1 also amended other provisions of the 2015 Collaboration Agreement, including the expiration terms.

In connection with the 2015 Collaboration Agreement, Vertex made a nonrefundable upfront payment of $75.0 million. Under the 2015 Collaboration Agreement, Vertex agreed to fund the discovery activities conducted pursuant to the agreement while retaining options to co-exclusive and exclusive licenses. In December 2017, upon execution of the JDA and Amendment No. 1, Vertex exercised its option to obtain a co-exclusive license to develop and commercialize hemoglobinopathy and beta-globin targets. As such, for potential hemoglobinopathy treatments, including treatments for sickle cell disease, the Company and Vertex will share equally all research and development costs and worldwide revenues. In connection with the JDA, the Company received a $7.0 million up-front payment from Vertex and subsequently received a one-time low seven-digit milestone payment upon the dosing of the second patient in a clinical trial with the initial product candidate. In addition, upon execution of the JDA and Amendment No. 1, it was clarified that Vertex may elect to license up to four remaining targets, for which it will lead global development and commercialization activities and the Company received the right to receive up to $420.0 million in development, regulatory and commercial milestones and royalties on net product sales for each of the targets (inclusive of $10 million due upon exercise of each exclusive option).

In June 2019, the Company and Vertex entered into a series of agreements, which closed on July 23, 2019, including a strategic collaboration and license agreement, or the 2019 Collaboration Agreement, for the development and commercialization of products for the treatment of Duchenne muscular dystrophy, or DMD, and Myotonic Dystrophy Type 1, or DM1. Under the terms of the 2019 Collaboration Agreement, the Company received an upfront, nonrefundable payment of $175.0 million. In addition, the Company is eligible to receive potential aggregate payments of up to $825.0 million based upon the successful achievement of specified research, development, regulatory and commercial milestones for the DMD and DM1 programs. The Company is also eligible to receive tiered royalties on future net sales on any products that may result from this collaboration. For the DMD program, Vertex is responsible for all research, development, manufacturing and commercialization activities and all related costs. For the DM1 program, the Company will perform specified guide RNA research and Vertex is responsible for all other research, development, manufacturing and commercialization costs. Upon Investigational New Drug, or IND, application filing, the Company has the option to forego the DM1 milestones and royalties and instead, co-develop and co-commercialize all DM1 products globally in exchange for payment of 50% of research and development costs incurred by Vertex from the effective date of the agreement through IND filing.

In connection with the execution of the 2019 Collaboration Agreement, the Company and Vertex entered into a second amendment to the 2015 Collaboration Agreement, or Amendment No. 2. Among other things, Amendment No. 2 modified certain definitions and provisions of the 2015 Collaboration Agreement to make them consistent with the 2019 Collaboration Agreement and set forth the number and identity of the collaboration targets under the 2015 Collaboration Agreement. The Company and Vertex agreed that one of the four remaining options under the 2015 Collaboration Agreement, as amended, would not be exercised; instead, the Company will reacquire the exclusive rights and will conduct research and development activities for the specified target. Vertex will have the option to co-develop and co-commercialize the specified target upon IND filing in exchange for payment of 50% of research and development costs incurred by the Company from the effective date of the agreement through IND filing. If Vertex does not exercise its option to co-develop and co-commercialize the specified target, Vertex is eligible to receive up to $395.0 million in potential specified research, development, regulatory and commercial milestones and tiered single-digit royalties on future net sales.

In October 2019, Vertex exercised the remaining three options granted to it under the 2015 Collaboration Agreement to exclusively license the collaboration targets developed under the 2015 Collaboration Agreement, resulting in a payment of $30.0 million to the Company in the fourth quarter of 2019. In addition, the Company achieved the first milestone under the 2019 Collaboration Agreement in the first quarter of 2020 and, in connection therewith, received a payment of $25.0 million in April 2020.

Accounting for the Vertex Agreements

The 2015 Collaboration Agreement, Amendment No. 1, and JDA are collectively the “2015 Agreements” and the 2019 Collaboration Agreement and Amendment No. 2. are collectively the “2019 Agreements.” The 2015 Collaboration Agreement, Amendment No. 1, Amendment No. 2, JDA and 2019 Collaboration Agreement are collectively the “Vertex Agreements.”

The Vertex Agreements include components of a customer-vendor relationship as defined under ASC 606, collaborative arrangements as defined under ASC 808 and research and development costs as defined under ASC 730, Research and Development, or ASC 730.

Accounting Analysis Under ASC 606

Accounting for the 2019 Agreements

Identification of the Contract

The 2019 Agreements represented a contract modification to the 2015 Agreements. As a result, the 2019 Agreements and the 2015 Agreements are combined for accounting purposes and treated as a single arrangement.

Identification of Performance Obligations

The Company concluded the following material promises were both capable of being distinct and distinct within the context of the Vertex Agreements and represented separate performance obligations: (i) an exclusive license for worldwide rights for DMD gene editing products, or DMD License; (ii) an exclusive license for worldwide rights for DM1 gene editing products, or DM1 License; (iii) the performance of specified guide RNA research for DM1, or DM1 R&D Services; (iv) a material right representing the option to obtain a co-exclusive development and commercialization license for a specified target, or Specified Target Option; (v) three material rights representing the option for up to three exclusive licenses to develop and commercialize the collaboration targets, or Collaboration Target Options, and (vi) the waiving of Vertex’s material right associated with its option to a fourth exclusive license in connection with the Company’s reacquisition of exclusive rights to the specified target.

Determination of Transaction Price

The overall transaction price was determined based on the remaining transaction price from the 2015 Agreements, as well as the transaction price from the 2019 Agreements. The transaction price includes variable consideration estimated using the most likely amount methodology. As such, the Company determined the transaction price totaling $268.6 million was comprised of: (i) $57.8 million of pre-existing deferred revenue from the 2015 Agreements; (ii) non-cash consideration of $10.0 million related to the waiving of Vertex’s material right associated with its option to a fourth exclusive license in connection with the Company’s reacquisition of exclusive rights to the specified target; (iii) an upfront payment of $175.0 million; (iv) variable consideration of $25.0 million which represented the Company’s estimate related to a near-term research and development milestone for which the Company determined that it is not probable that a significant reversal of cumulative consideration will occur at the onset of the transaction; and (v) variable consideration of $0.8 million which represents the Company’s estimate of payments from Vertex for DM1 R&D Services.

The Company determined that all other possible variable consideration resulting from milestones and royalties discussed above was fully constrained as of December 31, 2020. The Company will re-evaluate the transaction price in each reporting period.

Allocation of Transaction Price to Performance Obligations

The selling price of each performance obligation was determined based on the Company’s estimated standalone selling price, or the ESSP. The Company developed the ESSP for all the performance obligations included in the Vertex Agreements with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. The Company then allocated the transaction price to each performance obligation on a relative standalone selling price basis.

The ESSP for the DMD License and DM1 License was determined to be $224.6 million and $76.2 million, respectively. The ESSP was determined based on probability and present value adjusted cash flows from projected worldwide net profit for each of the respective programs based on probability assessments, projections based on internal forecasts, industry data, and information from other guideline companies within the same industry and other relevant factors. On a relative basis, $151.1 million and $51.3 million of the transaction price was allocated to the DMD License and DM1 License, respectively.

The ESSP for the Specified Target Option material right was determined to be $17.5 million, which was based on the incremental discount between (i) the value of the probability and present value adjusted cash flows from the equal sharing of projected worldwide net profit increased by the value of the option provided to Vertex less (ii) the expected exercise price at the time of option exercise. The present value adjusted cash flows also considered projections based on internal forecasts, industry data, and information from other guideline companies within the same industry and other relevant factors. On a relative basis $11.8 million of the transaction price was allocated to the Specified Target Option material right.

The ESSP for each of the three Collaboration Target Option material rights was determined to be $25.0 million, $22.2 million and $22.2 million, respectively, which was determined based on the probability and present value adjusted cash flows from milestone payments owed for exclusive licenses, less the price paid to exercise each option. On a relative basis, $46.7 million of the transaction price was allocated to the Collaboration Target Option material rights.

The aforementioned ESSPs reflect the level of risk and expected probability of success inherent in the nature of the associated research area.

The ESSP for the waiving of Vertex’s material right associated with its option to a fourth exclusive license under the 2015 Agreements was determined to be $10.0 million, or the contractual value of the option. On a relative basis, $6.7 million of the transaction price was allocated to the waiving of Vertex’s material right associated with its option to a fourth exclusive license under the 2015 Agreements.

The ESSP for the DM1 R&D Services was determined to be $1.7 million, which was based on estimates of the associated effort and cost of the services, adjusted for a reasonable profit margin that would be expected to be realized under similar contracts. On a relative basis, $1.1 million of the transaction price was allocated to the DM1 R&D Services.

Recognition of Revenue

The Company determined that the DMD License and DM1 License represent functional intellectual property, as the intellectual property provides Vertex with the ability to perform a function or task in the form of research and development. As such, the revenue related to the licenses was recognized at the point in time in which they were delivered during the third quarter of 2019.

The revenue allocated to the waiving of Vertex’s material right associated with its option to a fourth exclusive license in connection with Company’s reacquisition of exclusive rights to the specified target was recognized at the point in time in which the option was waived, on the effective date of the 2019 Agreements.

The Company concluded that the Specified Target Option and Collaboration Target Options were considered material rights under the Vertex Agreements. Revenue related to the three Collaboration Target Options material right was recognized at the point in time in which Vertex exercised the Collaboration Target Options, which occurred in the fourth quarter of 2019.

The Company recognizes revenue related to the DM1 R&D Services over time as the services are rendered, which was originally expected to be over an 18-month period from the effective date of the 2019 Agreements and is now expected to be over a 24-month period from the effective date of the 2019 Agreements.

Accounting for the 2015 Agreements (prior to the execution of the 2019 Agreements)

On January 1, 2018, the Company adopted ASC 606 using the modified retrospective approach. The Company applied the practical expedient in ASC 606-10-65-1 in identifying the satisfied and unsatisfied performance obligations, determining the transaction price and allocating the transaction price under the practical expedient in ASC 606. There was no significant impact on revenue recognized under ASC 606 and the prior revenue recognition as a result of the adoption.

Identification of the Contract

Amendment No. 1 and the JDA represented a contract modification to the 2015 Collaboration Agreement. As a result, the 2015 Agreements are combined for accounting purposes and treated as a single arrangement.

Identification of Performance Obligations

The Company concluded the following material promises were both capable of being distinct and distinct within the context of the 2015 Agreements and represented separate performance obligations: (i) the non-exclusive research license; (ii) four material rights representing the option for up to four exclusive licenses to develop and commercialize the collaboration targets; (iii) a combined performance obligation representing the co-exclusive research license, and a development and commercialization license to develop and commercialize hemoglobinopathies and beta-globin targets; and (iv) the performance of R&D Services.

Determination of Transaction Price

The overall transaction price was comprised of: (i) original upfront payment of $75.0 million, (ii) an upfront payment of $7.0 million under the JDA, and (iii) $19.3 million of variable consideration associated with the R&D services.

The Company determined that all other possible variable consideration resulting from milestones and royalties discussed above was fully constrained at the time of the transaction.

Allocation of Transaction Price to Performance Obligations

The selling price of each performance obligation was determined based on the Company’s ESSP. The Company developed the ESSP for all the performance obligations included in the 2015 Agreements with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. The Company then allocated the transaction price to each performance obligation on a relative standalone selling price basis.

The ESSP for R&D Services was determined to be $19.3 million. The Company developed the ESSP for the R&D Services primarily based on the nature of the services to be performed and estimates of the associated effort and cost of the services, adjusted for a reasonable profit margin that would be expected to be realized under similar contracts. The Company allocated $19.3 million of the transaction price to R&D Services.

The Company’s ESSP for each of the remaining material rights to obtain an exclusive license to develop and commercialize a single collaboration target are $45.6 million, $38.4 million, $17.3 million and $17.3 million for a total of $118.6 million. ESSPs for these items were determined based on the probability and present value adjusted cash flows from milestone payments owed for exclusive licenses, less the price paid to exercise each option. On a relative basis $57.7 million of the transaction price was allocated to these material rights.

The Company’s ESSP for the co-exclusive research license and the development and commercialization licenses for hemoglobinopathy and beta-globin targets is $48.9 million. The ESSP for this item was determined based on probability and present value adjusted cash flows from the equal sharing of projected worldwide net profit. ESSP reflects the level of risk and expected probability of success inherent in the nature of the associated research area. On a relative basis $23.8 million of the transaction price was allocated to the co-exclusive research license and the development and commercialization licenses for hemoglobinopathy and beta-globin targets.

The Company used a market-based approach to determine the ESSP of the non-exclusive research license of $1.0 million. The Company determined ESSP by use of comparative data, including in-licensed research agreements negotiated and executed within the Company. On a relative basis, $0.5 million of the transaction price was allocated to the non-exclusive research license.

The aforementioned ESSPs reflect the level of risk and expected probability of success inherent in the nature of the associated research area.

Recognition of Revenue

The Company determined that the non-exclusive research license is symbolic intellectual property as Vertex receives value from the license through the Company’s ongoing activities, and, as such, the revenue related to the non-exclusive research license was recognized ratably over the term of the arrangement. Upon the execution of the JDA, a co-exclusive research, development and commercialization license was granted for hemoglobinopathy and beta-globin targets. The Company determined that the revenue related to these licenses was recognized at a point in time, in which they were delivered at inception of the JDA in December 2017. As Vertex has the material right in its option to obtain four additional exclusive licenses to develop and commercialize four additional collaboration targets, the Company determined that consideration allocated to these material rights would be included in the transaction price of the exclusive license and recognized at a point in time, upon the exercise of the option by Vertex or expiration. As the Company has a right to consideration from Vertex in an amount that corresponds directly with the value of the Company’s

performance completed to date for the R&D services, the Company recognized revenue related to the R&D services as invoiced, in line with the practical expedient in ASC 606-10-55-18.

Revenue recognized in connection with the Vertex Agreements

Revenue recognized under the Vertex Agreements for the year ended December 31, 2020 was $0.5 million and was comprised of research and development services.

Revenue recognized under the Vertex Agreements for the year ended December 31, 2019 was $289.1 million. The $289.1 million of revenue recognized for the year-ended December 31, 2019 was comprised of (i) revenue related to the DMD License and DM1 License of $202.4 million, which was recognized at the point in time in which the licenses were delivered, (ii) revenue related to the Collaboration Target Options material right of $76.7 million, which was recognized upon the exercise of the Collaboration Target Options by Vertex and is inclusive of the $30.0 million payment made by Vertex to exercise those options, (iii) revenue allocated to the waiving of Vertex’s material right associated with its option to a fourth exclusive license in connection with the Company’s reacquisition of exclusive rights to the specified target of $6.7 million, which was recognized at the point in time in which the option was waived, (iv) revenue recognized in connection with DM1 R&D Services of $0.1 million and (v) revenue recognized of $0.1 million related to both research and development services as well as the amortization of the non-exclusive research license under the 2015 Agreements. Additionally, the Company recognized revenue related to a one-time low seven-digit milestone payment upon the dosing of the second patient in a clinical trial with the initial product candidate in the third quarter of 2019.

Revenue recognized under the Vertex Agreements for the year ended December 31, 2018 was $0.6 million and was comprised of research and development services, as well as the amortization of the non-exclusive research license under the 2015 Agreements.

As of December 31, 2020 and 2019 there was $0.4 million and $0.9 million of current deferred revenue related to the collaboration with Vertex, respectively. As of December 31, 2020, there was $11.8 million of non-current deferred revenue related to the collaboration with Vertex, which is unchanged from December 31, 2019. The transaction price allocated to the remaining performance obligations was $11.9 million.

Future Milestones under the Vertex Agreements

The Company has evaluated the milestones that may be received in connection with the Vertex Agreements. As discussed above, the Company is eligible to receive up to $410.0 million in additional development, regulatory and commercial milestones and royalties on net product sales for each of the three collaboration targets that Vertex licensed in the fourth quarter of 2019. Each milestone is payable only once per collaboration target, regardless of the number of products directed to such collaboration target that achieve the relevant milestone event.

The Company is eligible to receive additional potential future payments of up to $800.0 million based upon the successful achievement of specified research, development, regulatory and commercial milestones for the DMD and DM1 programs. The Company is also eligible to receive tiered royalties on future net sales on any products that may result from this collaboration; however, the Company has the option to forego the DM1 milestones and royalties to co-develop and co-commercialize all DM1 products globally.

Each of the remaining milestones are fully constrained as of December 31, 2020. There is uncertainty that the events to obtain the research and developmental milestones will be achieved given the nature of clinical development and the stage of the CRISPR/Cas9 technology. The remaining research, development and regulatory milestones will be constrained until it is probable that a significant revenue reversal will not occur. Commercial milestones and royalties relate predominantly to a license of intellectual property and are determined by sales or usage-based thresholds. The commercial milestones and royalties are accounted for under the royalty recognition constraint and will be accounted for as constrained variable consideration. The Company applies the royalty recognition constraint for each commercial milestone and will not recognize revenue for each until the subsequent sale of a licensed product (achievement of each) occurs.

Accounting Analysis under ASC 808

In connection with the 2019 Agreements, the Company identified the following collaborative elements, which were unchanged as those identified with the 2015 Agreements and are accounted for under ASC 808: (i) development and commercialization services for shared products; (ii) R&D Services for follow-on products; and (iii) committee participation. The related impact of the cost sharing associated with research and development is included in research and development expense. Expenses related to services performed by the Company are classified as research and development expense. Payments received from Vertex for partial reimbursement of expenses are recorded as a reduction of research and development expense.

During the years ended December 31, 2020, 2019 and 2018, the Company recognized $48.6 million, $29.2 million and $20.2 million of research and development expense related to the Vertex Agreements, respectively. Research and development expense for 2020, 2019 and 2018 is net of $28.2 million, $15.9 million and $13.8 million of reimbursements from Vertex, respectively.

Accounting Analysis under ASC 730

In connection with the 2019 Vertex Agreements, the Company and Vertex agreed that one of the four remaining options under the 2015 Agreements, as amended, would not be exercised; instead, the Company will conduct research and development activities for a specified target. Vertex will have the option to co-develop and co-commercialize the specified target upon IND filing in exchange for payment of 50% of research and development costs incurred by the Company from the effective date of the agreement through IND filing. If Vertex does not exercise its option to do so within a specified time period, Vertex is eligible to receive up to $395.0 million in potential specified research, development, regulatory and commercial milestones and tiered single-digit royalties on future net sales.

In connection therewith, the Company determined that in order for the Company to obtain the right to conduct research and development activities on the specified target, the Company had waived its right to receive an option exercise payment of $10.0 million from Vertex, which was included as non-cash consideration in the transaction price for the 2019 Agreements described above. The Company then subsequently reacquired its rights to the specified target by waiving payment owed by Vertex of $10.0 million for a license that represents in-process research and development and therefore, $10.0 million of non-cash consideration was fully expensed upon the execution of the 2019 Agreements. The Company also determined that research and development services through IND for the specified target and any payment of future development and commercialization milestones, as well as sales-based milestones and royalties for the specified target, would be accounted for as research and development costs under ASC 730 and expensed as incurred. In addition, the Company also determined that should the Company elect its option to co-develop and co-commercialize all DM1 products globally, it will record the option fee as research and development expense upon exercise.

Agreements with Bayer Healthcare LLC

Summary

On December 19, 2015, the Company entered into an agreement with Bayer, to establish a joint venture to focus on the research and the development of new therapeutics to cure blood disorders, blindness and congenital heart disease. On February 12, 2016, the Company and Bayer completed the formation of the joint venture entity, Casebia. Bayer and the Company each received a 50% equity interest in the entity in exchange for their respective contributions to the entity. At that time, the Company also entered into a separate service agreement with Casebia, under which the Company agreed to provide compensated research and development services. Collectively, these agreements are referred to as the “2015 Casebia Agreements.”

On December 13, 2019, the Company, Bayer and Casebia entered into a series of transactions by which, among other things, the Company acquired 100% of the partnership interests in Casebia, or the Retirement Agreement, the Company and Bayer terminated their joint venture, or the Joint Venture Termination Agreement, and the Company and Bayer entered into a new option agreement, or the 2019 Option Agreement. Collectively, these agreements are referred to as the “2019 Casebia Agreements.”

In connection with the Retirement Agreement, Casebia retired Bayer’s outstanding partnership interests in exchange for $22.0 million returned from Casebia operating cash less certain estimated interim operating expenses of $6.0 million, and the Company acquired 100% of the partnership interests in Casebia.

In connection with entering into the Retirement Agreement, the Company, Bayer and Casebia entered into the Joint Venture Termination Agreement. In connection therewith, the Company and Bayer agreed to terminate the Joint Venture Agreement from December 2015. Under the Joint Venture Termination Agreement, Casebia-owned patents are now co-owned by the Company and Bayer, subject to certain exclusive licenses granted therein. Under the Joint Venture Termination Agreement, the Company and Bayer each retained rights to their respective contributed intellectual property.

In connection with entering into the Retirement Agreement and the Joint Venture Termination Agreement, the Company and Bayer also entered into the 2019 Option Agreement, under which, among other things, the Company committed to invest a specified amount in certain research and development activities as described under “Accounting Analysis – Accounting for 2019 Casebia Agreements.” In addition, Bayer has an option (exercisable during a specified exercise period defined by future events, but in no event longer than 5 years after the effective date of the 2019 Option Agreement) to co-develop and co-commercialize two products for the diagnosis, treatment or prevention of certain autoimmune disorders, eye disorders, or hemophilia A disorders. In the event Bayer elects to co-develop and co-commercialize a product, the parties will negotiate and enter into a co-development and co-commercialization agreement, or the Co-Commercialization Agreement, for such product, and Bayer would be responsible for 50% of

the research and development costs incurred by the Company for such product going forward. Bayer would receive 50% of all profits from sales of such product and would be responsible for 50% of all losses.

If Bayer elects to exercise its option to co-develop and co-commercialize a product, Bayer will make a one-time $20.0 million payment, or the “Option Payment”, to the Company that will become non-refundable once the parties execute a Co-Commercialization Agreement with respect to such optioned product. The Option Payment is payable only once with respect to the first time Bayer exercises an option under the 2019 Option Agreement.

In addition, following Bayer’s exercise of its option and/or the execution of the Co-Commercialization Agreement for an optioned product, for a period beginning on the effective date of such Co-Commercialization Agreement and ending on the earlier of the three month anniversary of such effective date or during the 90-day negotiation process of such Co-Commercialization Agreement, Bayer has a right to negotiate an exclusive license to develop and commercialize such optioned product. If Bayer exercises such right, the parties will enter into an exclusive license agreement for such optioned product on terms mutually agreeable to the parties. Further, the Option Payment paid for such optioned product would become credited against payments due under such exclusive license or any other exclusive license entered into in connection with the 2019 Option Agreement.

Either party may terminate the 2019 Option Agreement upon the other party’s material breach, subject to specified notice and cure provisions. The Company may also terminate the 2019 Option Agreement in the event Bayer commences or participates in any action or proceeding challenging the validity or enforceability of any Company patent necessary or useful for the research, development, manufacture or commercialization of a product that is the subject of the 2019 Option Agreement. Bayer may also terminate the 2019 Option Agreement upon the Company’s bankruptcy or insolvency, or for convenience at any time, after giving written notice.

Accounting Analysis

Accounting for the 2015 Casebia Agreements

The Company determined that Casebia was a VIE and concluded that the Company was not the primary beneficiary of the VIE. As such, the Company did not consolidate Casebia’s results into the consolidated financial statements. Instead, the Company accounted for its ownership in Casebia as an equity method investment, the value of which was written down to zero immediately after formation of the joint venture. The 2015 Casebia Agreements included components of a customer-vendor relationship as defined under ASC 606 and collaborative arrangements as defined under ASC 808.

As discussed above, on January 1, 2018, the Company adopted ASC 606 using the modified retrospective approach. There was no significant impact on revenue recognized under ASC 606 and the prior revenue recognition as a result of the adoption.

For the years ended December 31, 2019 and 2018, the only element of 2015 Casebia Agreements accounted for in accordance with ASC 606 was the obligation to perform research and development services for Casebia. Revenue recognized for research and development was recognized under the right to invoice practical expedient in ASC 606-10-55-18. This performance obligation was terminated upon the execution of the 2019 Casebia Agreements.

For the years ended December 31, 2019 and 2018, the only element of the 2015 Casebia Agreements accounted for in accordance with ASC 808 was the cost sharing activity with Casebia with respect to shared research and technology licenses with other vendors for which the Company determined the arrangement was a cost/profit sharing arrangement and not a revenue arrangement. Therefore, the related impact of the cost sharing is included in R&D expense. Cost sharing activity ceased with the execution of the 2019 Casebia Agreements.

Loss from Equity Method Investment

During the years ended December 31, 2019 and 2018, the Company recognized $5.5 million and $4.3 million, respectively, of stock-based compensation expense related to Casebia employees. Unrecognized equity method losses in excess of the Company’s equity investment in Casebia was $72.0 million as of December 31, 2019. Total net loss of Casebia for the period ending December 13, 2019 (prior to the Company’s consolidation of Casebia) and the year ended December 31, 2018 were $58.8 million and $52.5 million, respectively.

Collaboration Revenue

During the years ended December 31, 2019 and 2018, the Company recognized $0.5 million and $2.5 million of revenue, respectively, related to the collaboration with Casebia. During the years ended December 31, 2019 and 2018, the Company recognized $0.7 million and $3.8 million of research and development expense, respectively, in relation to its performance under the agreement.

Collaborative elements

The Company received reimbursements of $0.2 million and $0.9 million for both research and license agreements during years ended December 31, 2019 and 2018, respectively, which was recorded as a reduction of R&D expense in the income statement.

Accounting for the 2019 Casebia Agreements

The Company determined that the Retirement Agreement and Joint Venture Termination Agreement resulted in the Company obtaining a controlling interest in Casebia and should be accounted for as a separate component from the 2019 Option Agreement. In doing so, the Company allocated the consideration transferred of $41.0 million (consisting of $16.0 million of assets acquired net of the purchase price, as displayed in the table below, and $25.0 million of cash allocated to the 2019 Option Agreement) between the two components using a relative fair value approach. The Company determined the relative fair value related to obtaining a controlling interest in Casebia was $32.0 million and the relative fair value of the consideration transferred related to the 2019 Option Agreement was $25.0 million, which is comprised of $20.2 million related to certain research and development activities and $4.8 million related to certain options as described above.

As a result of the Retirement Agreement, the Company determined that it had obtained a controlling interest in a VIE, for which it became the primary beneficiary. As such, under ASC 810, Consolidation, the Company accounted for the net assets obtained under ASC 805, Business Combinations. In accordance therewith, the Company determined the set of acquired assets and assumed liabilities did not meet the definition of a business, as the Company did not acquire an assembled workforce and thus the Company did not acquire substantive processes capable of producing outputs. As such, no goodwill was recorded. The Company measured the fair value of the assets and liabilities received, determining the relative fair value was $16.0 million (after paying the $16.0 million for Bayer’s 50% interest) and recorded the difference between that amount and the Company’s carrying amount, which was zero, as a gain within other income (expense). The relative fair value of the assets and liabilities received (exclusive of the $16.0 million paid from Casebia to Bayer to retire Bayer’s interest in the JV) was determined as follows (in thousands):

Fair value	Amount
Cash and cash equivalents	$	6,784
Prepaid expenses and other current assets		2,565
Property, plant and equipment, net		9,340
Operating lease assets		11,003
Restricted cash		1,226
Accrued expenses and other current liabilities		(3,915	)
Operating lease liabilities		(11,003	)
Net assets	$	16,000

The value of the reacquired rights related to the intellectual property was determined to be insignificant.

The Company determined that the 2019 Option Agreement should be accounted for under ASC 730-20, Research and Development Expense. This determination was based on the fact that the financial risk associated with the research and development has been transferred to the Company because repayment of any of the funds provided by Bayer depends solely on the results of the research and development having a future economic benefit. The Company further determined that it had two separate obligations under the 2019 Option Agreements, which consist of i) research and development services and ii) future delivery of up to two options for products in defined fields. The relative fair value of the obligations was determined to be $20.2 million and $4.8 million, respectively. As the Company has accounted for its obligations as a contract to perform research and development for others, with respect to the obligation to perform research and development services the Company will recognize an offset to research and development expense as the research is performed and, with respect to the future delivery of up to two option for products in defined fields, at the earlier of option exercise (at or near IND application filing), expiration, or when commercially reasonable efforts to progress the program have been exhausted.

During the year ended December 31, 2020, the Company recorded a benefit of $13.2 million to research and development expense for qualifying expenses incurred under the 2019 Option Agreement. The Company has recorded $7.0 million in other current

liabilities relating to certain research and development obligations to be satisfied within one year of the balance sheet date and $4.8 million in other long-term liabilities consisting of the relative fair value of such obligations to be satisfied beyond one year from the balance sheet date as well as the relative fair value of the options.

Collaboration Agreement with ViaCyte, Inc.

On September 17, 2018, the Company entered into a research collaboration agreement (“ViaCyte Collaboration Agreement”) with ViaCyte, Inc. (“ViaCyte”) focused on the discovery, development, and commercialization of gene-edited allogeneic stem cell therapies for the treatment of diabetes. Under the terms of the ViaCyte Collaboration Agreement, the Company and ViaCyte will jointly seek to develop an immune-evasive stem cell line as a first step on the path to an allogeneic stem-cell derived product. Upon successful completion of these studies and identification of a product candidate, the parties will jointly assume responsibility for further development and commercialization worldwide.

Upon execution of the agreement, ViaCyte was entitled to receive $15.0 million from the Company payable in two installments either in cash or in common shares at the Company’s option. The agreement includes certain provisions such that in the event ViaCyte sold shares received from the Company for less than $15.0 million in combined net proceeds, the Company would owe ViaCyte the deficient amount. In the event ViaCyte sold shares received from the Company for greater than $15.0 million in combined net proceeds, ViaCyte would owe the Company the surplus amount. On September 24, 2018, the Company issued 165,636 common shares to ViaCyte which had a fair value of $7.5 million. These shares were subsequently sold for $6.9 million, resulting in a deficient amount of $0.6 million. On November 15, 2018, the Company issued 214,512 common shares to ViaCyte, which had a fair value of $8.1 million. These shares were subsequently sold for $7.5 million, resulting in a deficient amount of $0.6 million, which was paid in cash on December 18, 2018. Of the total consideration paid of $16.2 million, the Company recognized $15.0 million within research and development expense and $1.2 million within other (expense) income in the statement of operations for the twelve months ended December 31, 2018.

At the time of the agreement, ViaCyte had the option, under certain conditions, to receive an additional $10.0 million from the Company in the form of a convertible promissory note to be issued at fair value. As of November 2018, these conditions expired and the Company is no longer required to provide ViaCyte with additional funding. The ViaCyte Collaboration Agreement may remain in force for up to six years. Under the agreement, each of the parties was obligated to use commercially reasonable efforts to perform certain research activities under a jointly developed research plan and each party bore the costs for its respective research obligations.

In 2019, the Company and ViaCyte amended the terms of the original agreement to, among other things, provide for a cost share of specified costs, in which the Company agreed to pay 60% of the specified costs and ViaCyte agreed to pay 40% of specified costs. The Company accounts for the arrangements under ASC 808 and does not consider the costs incurred to date material to the Company’s overall operations.

Share Capital

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Share Capital

10. Share Capital

The Company had 115,172,786 and 103,901,006 million authorized Common Shares as of December 31, 2020 and 2019, respectively, with a par value of CHF 0.03 per share. Share Capital consisted of the following:

		As of December 31,
Type of Share Capital	Conditional Capital	2020		2019
Common shares	Registered share capital		75,133,951		61,036,566
Common shares	Authorized share capital		17,625,426		19,246,503
Common shares	Conditional share capital - Bonds or similar debt instruments		4,919,700		4,919,700
Common shares	Conditional share capital - Employee benefit plans		17,493,709		18,698,237
	Total		115,172,786		103,901,006

Included in registered share capital are 2,906,383 shares registered, which are held by the Company and its subsidiaries and are reserved for future issuance for financings.

Common Share Issuances

Public Offerings

In October 2016, the Company sold 4.4 million common shares through an initial public offering (inclusive of shares sold pursuant to an overallotment option granted to the underwriters in connection with the offering) at a price of $14.00 per share for proceeds of $53.7 million, which were net of equity issuance costs of $8.3 million. Concurrent with the initial public offering, the

Company sold 2.5 million common shares to Bayer BV in a private placement, at a price of $14.00 per share, resulting in aggregate net proceeds of $35.0 million.

In January 2018, the Company completed an underwritten public offering of 5.7 million common shares (inclusive of shares sold pursuant to an overallotment option granted to the underwriters in connection with the offering), which were sold at a price of $22.75 per share. This offering resulted in aggregate net proceeds of $122.6 million, which were net of equity issuance costs of $8.2 million.

In September 2018, the Company completed an underwritten public offering of 4.2 million common shares, which sold at a price of $47.50 per share. This offering resulted in aggregate net proceeds of $184.5 million, which were net of equity issuance costs of $12.4 million. Additional equity issuance costs of $3.1 million for stamp taxes related to the January 2018 and September 2018 offerings were also paid in 2018.

In November 2019, the Company sold 4.9 million common shares through an underwritten public offering (inclusive of shares sold pursuant to the exercise of the underwriters’ option to purchase additional shares at a public offering price of $64.50 per share for aggregate net proceeds of $297.4 million, which were net of equity issuance costs of $17.8 million. Additional equity issuance costs of $3.0 million for stamp taxes were also paid in 2019.

In July 2020, the Company sold 7.4 million common shares through an underwritten public offering (inclusive of shares sold pursuant to the exercise of the underwriters’ option to purchase additional shares) at a public offering price of $70.00 per share for aggregate net proceeds of $489.7 million, which were net of equity issuance costs of $27.6 million. Additional equity issuance costs of $4.9 million for stamp taxes were payable as of December 31, 2020.

At-the-Market Offerings

In the first quarter of 2019, the Company began to issue and sell securities under an Open Market Sale Agreement^SM entered into with Jefferies LLC, or Jefferies, in August 2018, under which the Company was able to offer and sell, from time to time, common shares having aggregate gross proceeds of up to $125.0 million, or the 2018 ATM. During the year ended December 31, 2019, the Company issued and sold an aggregate of 2.8 million common shares at an average price of $44.38 per share for aggregate net proceeds of $120.6 million, which were net of equity issuance costs of $4.4 million. In addition, the Company paid approximately $0.9 million in stamp taxes during the year ended December 31, 2019 and accrued an additional $0.3 million for stamp taxes as of December 31, 2019. The Company paid the $0.3 million for stamp taxes in 2020.

In August 2019, the Company entered into a new Open Market Sale Agreement^SM with Jefferies under which the Company was able to offer and sell, from time to time at our sole discretion through Jefferies, as our sales agent, our common shares, par value of CHF 0.03 per share, or the August 2019 Sales Agreement. In August 2019, the Company filed a prospectus supplement with the SEC to offer and sell, from time to time, common shares having aggregate gross proceeds of up to $200.0 million, or the 2019 ATM. In connection with the Company’s entry into the August 2019 Sales Agreement, the August 2018 Open Market Sale Agreement^SM with Jefferies was mutually terminated by the Company and Jefferies. During the year ended December 31, 2020, the Company issued and sold an aggregate of 2.2 million common shares under the 2019 ATM at an average price of $89.47 per share for aggregate proceeds of $195.5 million, which were net of equity issuance costs of $4.5 million.

In December 2020, in connection with the August 2019 Sales Agreement, the Company filed a prospectus supplement with the SEC to offer and sell, from time to time, common shares having aggregate gross proceeds of up to $350.0 million, or the 2020 ATM. During the year ended December 31, 2020, the Company issued and sold an aggregate of 1.8 million common shares under the 2020 ATM at an average price of $169.57 per share for aggregate proceeds of $298.0 million, which were net of equity issuance costs of $4.5 million. Additional equity issuance costs for stamp taxes related to shares sold in 2020 related to the 2019 and 2020 ATM were $4.9 million, of which $4.0 million was payable as of December 31, 2020.

In January 2021, the Company issued and sold under the 2020 ATM an aggregate of 0.3 million common shares at an average price of $162.46 per share with aggregate proceeds of $46.7 million, which were net of equity issuance costs of $0.7 million. An additional $0.5 million of stamp taxes will be owed on this amount.

In January 2021, in connection with the August 2019 Sales Agreement, the Company filed a prospectus supplement with the SEC to offer and sell, from time to time, common shares having aggregate gross proceeds of up to $600.0 million. Through the date of issuance of this Annual Report on Form 10-K, the Company has issued and sold an aggregate of 1.1 million common shares under the 2021 ATM at an average price of $169.82 per share for aggregate proceeds of $177.8 million, which were net of equity issuance costs of $2.4 million. An additional $1.8 million of stamp taxes will be owed on this amount.

The Common Shares have the following characteristics:

Voting Rights

The holders of Common Shares are entitled to one vote for each Common Share held at all meetings of shareholders.

Dividends

The holders of Common Shares are entitled to receive dividends, if and when resolved upon by the general meeting of shareholders based on a respective proposal by the Board of Directors and provided that the Company disposes of sufficient freely distributable reserves. As of December 31, 2020, no dividends have been declared or paid since the Company’s inception.

Liquidation

The holders of the Common Shares are entitled to share ratably in the Company’s assets available for distribution to shareholders in the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or upon the occurrence of a deemed liquidation event.

Equity-based Compensation

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity-based Compensation

11. Equity-based Compensation

Option and Grant Plans

In April 2015, the Company’s shareholders approved the 2015 Stock Option and Grant Plan, or the 2015 Plan, and in July 2016, the Company’s shareholders approved the 2016 Stock Option and Incentive Plan, or the 2016 Plan. In May 2018, the Company’s shareholders approved the 2018 Stock Option and Incentive Plan, or the 2018 Plan (collectively, the “Plans”). Subsequent to the IPO, no further options were granted under the 2015 Plan. The Plans provide for the issuance of equity awards in the form of restricted shares, options to purchase Common Shares which may constitute incentive stock options, or ISOs, or non-statutory stock options, or NSOs, unrestricted stock unit grants, and qualified performance and market-based awards to eligible employees, officers, directors, non-employee consultants and other key personnel. Terms of the equity awards, including vesting requirements, are determined by the Company’s board of directors, subject to the provisions of the Plans. Options granted by the Company typically vest over four years and have a contractual life of ten years. Restricted stock unit grants typically vest over two to three years.

Equity-Based Compensation Expense

The Company recognized stock-based compensation expense totaling $66.0 million, $49.5 million, and $39.3 million during the years ended December 31, 2020, 2019 and 2018, respectively. Stock‑based compensation expense by classification within the consolidated statements of operations and comprehensive income (loss) is as follows (in thousands):

	Years Ended December 31,
	2020		2019		2018
Research and development	$	35,120	$	23,273	$	17,557
General and administrative		30,898		20,784		17,428
Loss from equity method investment		—		5,467		4,275
Total	$	66,018	$	49,524	$	39,260

As of December 31, 2020, there was $132.5 million and $45.7 million of unrecognized compensation expense related to unvested stock options and restricted stock units, respectively, that is expected to be recognized over a weighted-average period of 2.8 and 2.1 years, respectively.

Stock Options

The fair value of each option issued to employees and non-employees was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Years Ended December 31,
	2020			2019			2018
Options granted		2,182,773			2,832,784			2,209,597
Weighted-average exercise price	$	68.91		$	39.16		$	51.73
Weighted-average grant date fair value	$	42.28		$	24.57		$	33.82
Assumptions:
Expected volatility		69.2	%		68.9	%		71.9	%
Expected term (in years)		6.0			6.0			6.0
Risk-free interest rate		0.6	%		2.2	%		2.8	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

The following table summarizes stock option activity under the Company’s equity award plans (intrinsic value in thousands):

	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2019		7,782,437		$	31.30		8.2	$	231,554
Granted		2,182,773		$	68.91
Exercised		(1,517,735	)	$	23.53
Cancelled or forfeited		(345,495	)	$	41.61
Outstanding at December 31, 2020		8,101,980		$	42.44		7.8		896,666
Exercisable at December 31, 2020		3,838,372		$	30.43		7.0	$	470,907
Vested and expected to vest at December 31, 2020		8,101,980		$	42.44		7.8	$	896,666

During 2020 and 2019, the Company did not grant stock option awards subject to performance-based or market-based vesting conditions. As of December 31, 2020, options to purchase 940,646 Common Shares subject to performance-based vesting conditions were vested, as performance conditions were achieved, and there were 81,387 options to purchase Common Shares subject to performance-based vesting conditions outstanding.

During 2017, the Company granted 150,000 options with market-based vesting conditions, of which 75% vest at the end of a three-year service period and 25% vest at the end of a four-year service period. Upon achieving a specified average stock price in prior years, the market condition was satisfied. Expense for the options is being recognized over the requisite service period. As of December 31, 2020, 112,500 of the stock options had vested.

The total intrinsic value (the amount by which the fair market value exceeded the exercise price) of stock options exercised during the year ended December 31, 2020, 2019 and 2018 was $104.2 million, $42.2 million and $38.3 million, respectively.

Restricted Stock

The following table summarizes the restricted stock activity under the Company’s equity award plans:

	Shares			Weighted- Average Grant Date Fair Value
Unvested balance at December 31, 2019		699,534		$	56.53
Granted		437,670			77.92
Vested		(204,650	)		42.92
Cancelled or forfeited		(38,462	)		46.33
Unvested balance at December 31, 2020		894,092		$	70.55

During the years ended December 31, 2020, 2019 and 2018, the total fair value of restricted stock vested was $21.6 million, $3.6 million and $11.3 million, respectively.

Award modifications

During the years ended December 31, 2020, 2019 and 2018, the Company modified the terms of certain equity awards held by departing employees, resulting in $0.6 million, $0.1 million, and $3.8 million of stock-based compensation expense, respectively. During the year ended December 31, 2019, the Company modified the terms of certain equity awards held by non-employees. The modifications resulted in $2.9 million in stock-based compensation expense recorded during the period. For the year ended December 31, 2020 and 2018, there were no modification of options held by non-employees.

Employee Stock Purchase Plan

On July 19, 2016, the Company’s board of directors adopted its 2016 Employee Stock Purchase Plan, or the ESPP Plan, which was subsequently approved by its shareholders and became effective on October 19, 2016. The ESPP Plan authorizes the initial issuance of up to a total of 0.4 million shares of the Company’s common stock to participating employees. The Company activated its ESPP Plan on January 1, 2020. Activity to date has not been material.

Net Income (Loss) Per Share Attributable to Common Shareholders

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Net Income (Loss) Per Share Attributable to Common Shareholders

12. Net (Loss) Income Per Share Attributable to Common Shareholders

Basic net (loss) income per share is calculated by dividing net (loss) income attributable to common shareholders by the weighted-average number of common shares outstanding during the period. Diluted net (loss) income per share is calculated by dividing the net (loss) income attributable to common shareholders by the weighted-average number of common share equivalents outstanding for the period, including any dilutive effect from outstanding stock options and warrants using the treasury stock method. The Company’s net (loss) income is net (loss) income attributable to common shareholders for all periods presented.

The following table sets forth the computation of basic and diluted net (loss) income per share for the periods ended (in thousands, except per share amounts):

	Year ended December 31,
	2020			2019		2018

Net (loss) income	$	(348,865	)	$	66,858	$	(164,981	)
Basic weighted-average common shares outstanding		65,949,672			54,392,304		47,964,368
Effect of potentially dilutive securities:
Outstanding options		—			2,406,962		—
Unvested restricted common shares		—			133,532		—
Diluted weighted-average common shares outstanding		65,949,672			56,932,798		47,964,368
Basic net (loss) income per common share	$	(5.29	)	$	1.23	$	(3.44	)
Diluted net (loss) income per common share	$	(5.29	)	$	1.17	$	(3.44	)

The Company did not include the securities in the following table in the computation of the net (loss) income per share calculations because the effect would have been anti-dilutive during each period:

	Year ended December 31,
	2020		2019		2018
Outstanding options		8,101,980		3,789,129		6,689,311
Unvested restricted common shares		894,092		108,625		327,342
ESPP		11,257		—		—
Total		9,007,329		3,897,754		7,016,653

401 (k) Savings Plan

12 Months Ended

Dec. 31, 2020

Compensation And Retirement Disclosure [Abstract]

401(k) Savings Plan

13. 401(k) Savings Plan

The Company established a defined‑contribution savings plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”) in November 2016. The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis. The Company contributed $1.9 million, $1.1 million and $0.6 million to the 401(k) Plan for the year ended December 31, 2020, 2019 and 2018, respectively.

- Definition

The entire disclosure for retirement benefits.

+ References

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+ Details

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

14. Income Taxes

The Company is subject to U.S. federal and various state corporate income taxes as well as taxes in foreign jurisdictions for the foreign parent and where foreign subsidiaries have been established.

Net loss before taxes

For the years ended December 31, 2020, 2019 and 2018, the (loss) income before provision for income taxes consist of the following (in thousands):

	Years Ended December 31,
	2020			2019		2018
Domestic	$	7,630		$	9,155	$	5,966
Foreign		(355,686	)		58,151		(170,394	)
Total	$	(348,056	)	$	67,306	$	(164,428	)

The (provision for) benefit from income taxes consist of the following (in thousands):

	Years Ended December 31,
	2020			2019			2018
Current income taxes:
Federal	$	(248	)	$	(423	)	$	(416	)
State		(151	)		(59	)		(131	)
Foreign		(1	)		0			0
Total current income taxes		(400	)		(482	)		(547	)
Deferred income taxes:
Federal		(409	)		34			(6	)
State		—			—			—
Foreign		—			—			—
Total deferred income taxes		(409	)		34			(6	)
Total income tax (provision) benefit	$	(809	)	$	(448	)	$	(553	)

A reconciliation of income tax expense computed at the statutory corporate income tax rate to the effective income tax rate for the years ended December 31, 2020, 2019 and 2018 is as follows:

	Years Ended December 31,
	2020			2019			2018
Income tax expense at statutory rate		11.9	%		9.3	%		9.3	%
State income tax, net of federal benefit		1.0	%		(2.1	)%		0.7	%
Nondeductible expenses		0.1	%		(0.1	)%		0.0	%
Foreign rate differential		(0.1	)%		2.0	%		(0.4	)%
Statutory to US GAAP permanent differences		0.0	%		0.1	%		1.0	%
Stock-based compensation		2.3	%		(2.0	)%		1.4	%
Impact of deferred rate change		0.0	%		(12.2	)%		0.0	%
Research credits		3.3	%		(5.2	)%		1.8	%
Change in valuation allowance		(18.7	)%		10.9	%		(14.1	)%
Effective income tax rate		(0.2	%)		0.7	%		(0.3	%)

The federal statutory rate reflects the Switzerland mixed company service rate.

Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets are comprised of the following (in thousands):

	Years Ended December 31,
	2020			2019
Deferred tax assets:
Net operating loss carryforwards	$	84,531		$	31,496
Accruals and reserves		4,785			2,868
Operating lease liabilities		16,782			14,214
Other deferred tax assets		1,517			28
Stock-based compensation		9,605			5,217
Deferred revenue		86			(20	)
Research credit		19,526			7,150
Total deferred tax assets		136,832			60,953
Less valuation allowance		(116,640	)		(45,913	)
Net deferred tax assets		20,192			15,040
Deferred tax liabilities:
Depreciation		(6,778	)		(3,901	)
Operating lease assets		(13,776	)		(11,068	)
Intangible assets		(31	)		(40	)
Other deferred tax liabilities		(4	)		(20	)
Total deferred tax liabilities		(20,589	)		(15,029	)
Long term deferred taxes	$	(397	)	$	11

The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company’s history of worldwide operating losses, the Company has concluded that it is more-likely-than-not that the benefit of its U.S. and non-U.S. deferred tax assets will not be realized. Accordingly, as of December 31, 2020 and 2019, the Company has provided a full valuation allowance against its net deferred tax assets in Switzerland, the United States and the U.K. for its TRACR subsidiary. The valuation allowance increased by $70.7 million during 2020, which is primarily attributable to increases in net operating loss carryforwards as a result of current year net losses.

As of December 31, 2020, the Company had available non-U.S. net operating loss carryforwards of $1,416.7 million of which $707.6 million relate to Switzerland, $707.6 million relate to the Canton of Zug, and $1.5 million relate to the Company’s wholly-owned subsidiary in the United Kingdom. The net operating losses generated in Switzerland and the Canton of Zug begin to expire in 2023 and the net operating losses generated in the United Kingdom can be carried forward indefinitely.

As of December 31, 2020, the Company had U.S. domestic federal research and development credit carryforwards of $13.9 million which expire in 2040 for federal purposes, which are net of uncertain tax positions of $7.5 million. As of December 31, 2020, the Company had U.S. domestic state research and development credit carryforwards of $6.9 million which begin to expire in 2034, which are net of uncertain tax positions of $4.5 million.

ASC 740 clarifies the accounting for uncertainty in income taxes recognized in an enterprise’s financial statement by prescribing the minimum recognition threshold and measurement of a tax position taken or expected to be taken in a tax return.

As of December 31, 2020, the Company had gross unrecognized tax benefits of $12.0 million of which $11.0 million would favorably impact the effective tax rate if recognized. The Company will recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2020, 2019 and 2018, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s consolidated statements of operations and comprehensive loss.

The aggregate changes in gross unrecognized tax benefits were as follows (in thousands):

	Years Ended December 31,
	2020			2019		2018
Balance at beginning of year	$	5,231		$	1,595	$	354
Increases for tax positions taken during current period		7,004			2,754		1,212
Increases for tax positions taken in prior periods		—			882		29
Decreases for tax positions taken during current period		—			—		—
Decreases for tax positions taken in prior periods		(268	)		—		—
Balance at end of year	$	11,967		$	5,231	$	1,595

The Company files income tax returns in the U.S. federal jurisdiction, Massachusetts and certain non-U.S. jurisdictions. The Company is subject to U.S. federal, Massachusetts and non-U.S. income tax examinations by authorities for tax years ending after December 31, 2016. Research credits generated in prior tax years that are closed for examination may still be adjusted upon future examination if they have or will be used in a future period. The Company is subject to income tax examinations by authorities in its non-U.S. jurisdictions for all years. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act, or the CARES Act, was enacted in the United States, the impact of which was not material.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2020

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

15. Selected Quarterly Financial Data (Unaudited)

The following table sets forth the Company’s quarterly financial data for the two years ended December 31, 2020.

	2020
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Total revenue	$	157		$	44		$	148		$	370
Total operating expenses		73,743			80,733			92,547			108,131
Loss from operations		(73,586	)		(80,689	)		(92,399	)		(107,761	)
Net loss		(69,731	)		(79,656	)		(92,439	)		(107,039	)
Net loss per common share:
Basic	$	(1.15	)	$	(1.30	)	$	(1.32	)	$	(1.50	)
Diluted	$	(1.15	)	$	(1.30	)	$	(1.32	)	$	(1.50	)
Weighted-average common shares outstanding:
Basic		60,847,683			61,420,746			70,143,481			71,282,096
Diluted		60,847,683			61,420,746			70,143,481			71,282,096

	2019
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Total revenue	$	328		$	318		$	211,928		$	77,016
Total operating expenses		48,751			55,301			72,765			66,033
Loss from operations		(48,423	)		(54,983	)		139,163			10,983
Net (loss) income		(48,408	)		(53,699	)		138,423			30,542
Net (loss) income per common share:
Basic	$	(0.93	)	$	(1.01	)	$	2.52		$	0.53
Diluted	$	(0.93	)	$	(1.01	)	$	2.40		$	0.51
Weighted-average common shares outstanding:
Basic		52,093,208			53,188,041			54,829,057			57,395,839
Diluted		52,093,208			53,188,041			57,598,901			60,233,927

Related Party Transactions

12 Months Ended

Dec. 31, 2020

Related Party Transactions

16. Related Party Transactions

Casebia

Prior to the termination of the joint venture, Casebia was a related party under ASC 850, Related Party Disclosures (“ASC 850”). Refer to Note 9, “Agreements with Bayer Healthcare LLC.”

Vertex

In the fourth quarter of 2018, upon becoming owners of record of more than 10% of the voting interest of the Company, Vertex became a related party under ASC 850. As of July 2, 2019, upon becoming owners of record of less than 10% of the voting interest of the Company, Vertex was no longer a related party under ASC 850. Refer to Note 9, “Agreements with Vertex Pharmaceuticals Incorporated and certain of its subsidiaries.”

Summary of Significant Accounting Policies and Basis of Presentation (Policies)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Basis of Presentation and Use of Estimates

Segment Information

Foreign Currency Translation and Transactions

Cash and Cash Equivalents

Restricted Cash

Marketable Securities

Other Receivables

Concentrations of Credit Risk and Off-balance Sheet Risk

Fair Value of Financial Instruments

Level 1 —

Quoted prices in active markets that are accessible at the market date for identical unrestricted assets or liabilities.

Level 2 —

Level 3 —

Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Property and Equipment

Asset		Estimated useful life
Computer equipment		3 years
Furniture, fixtures and other		5 years
Laboratory equipment		5 years
Leasehold improvements		Shorter of useful life or remaining lease term

Impairment of Long-lived Assets

Revenue Recognition

1) Identify the contract with the customer

2) Identify the performance obligations in the contract

3) Determine the transaction price

4) Allocate the transaction consideration to performance obligations in the contract

5) Recognize revenue when or as the Company satisfies a performance obligation

Contract Balances

Grant Revenue

Collaboration Arrangements

Research and Development Expenses

Leases

The adoption of ASC 842 had the following impact on the financial statements:

	January 1, 2019 Prior to ASC 842 Adoption		ASC 842 Adjustment			January 1, 2019 As Adjusted
Consolidated Balance Sheet Data (in thousands):
Prepaid expenses and other current assets⁽¹⁾	$	9,658	$	(553	)	$	9,105
Operating lease assets⁽²⁾	$	—	$	26,087		$	26,087
Deferred rent⁽³⁾⁽⁴⁾	$	1,026	$	(1,026	)	$	—
Deferred rent non-current⁽³⁾	$	11,052	$	(11,052	)	$	—
Operating lease liabilities⁽⁵⁾	$	—	$	4,930		$	4,930
Non-current operating lease liabilities⁽⁵⁾	$	—	$	32,682		$	32,682

(1) Represents reclassification of prepaid rent to operating lease assets.
(2) Represents capitalization of operating lease assets and reclassification of equipment licenses from prepaid expenses to operating lease assets, offset by reclassification of deferred rent to operating lease assets.
(3) Represents reclassification of deferred rent and tenant incentives to operating lease assets.
(4) As of December 31, 2018, the deferred rent balance was $1,202, which included $176 of sublease income received prior to year-end but not due until January 1, 2019.
(5) Represents recognition of operating lease liabilities.

Equity-Based Compensation Expense

Equity Based Compensation Expense

The Company expenses restricted stock unit awards to employees based on the fair value of the award on a straight-line basis over the associated service period of the award.

Patent Costs

Income Taxes

Comprehensive (Loss) Income

Variable Interest Entities

As described in Note 9, on December 13, 2019, Casebia became a fully-owned subsidiary and, as a result, the Company consolidated Casebia’s financial results accordingly from that point forward.

Net (Loss) Income Per Share Attributable to Common Shareholders

New Accounting Pronouncements - Recently Adopted

New Accounting Pronouncements – Recently Adopted

Credit Losses

New Accounting - Pronouncements Not Yet Adopted

New Accounting Pronouncements – Not Yet Adopted

ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

Summary of Significant Accounting Policies and Basis of Presentation (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Schedule of Estimated Useful Lives of Assets

Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows:

Asset		Estimated useful life
Computer equipment		3 years
Furniture, fixtures and other		5 years
Laboratory equipment		5 years
Leasehold improvements		Shorter of useful life or remaining lease term

Impact of Adoption ASC 842 on the Financial Statements

The adoption of ASC 842 had the following impact on the financial statements:

	January 1, 2019 Prior to ASC 842 Adoption		ASC 842 Adjustment			January 1, 2019 As Adjusted
Consolidated Balance Sheet Data (in thousands):
Prepaid expenses and other current assets⁽¹⁾	$	9,658	$	(553	)	$	9,105
Operating lease assets⁽²⁾	$	—	$	26,087		$	26,087
Deferred rent⁽³⁾⁽⁴⁾	$	1,026	$	(1,026	)	$	—
Deferred rent non-current⁽³⁾	$	11,052	$	(11,052	)	$	—
Operating lease liabilities⁽⁵⁾	$	—	$	4,930		$	4,930
Non-current operating lease liabilities⁽⁵⁾	$	—	$	32,682		$	32,682

(1) Represents reclassification of prepaid rent to operating lease assets.
(2) Represents capitalization of operating lease assets and reclassification of equipment licenses from prepaid expenses to operating lease assets, offset by reclassification of deferred rent to operating lease assets.
(3) Represents reclassification of deferred rent and tenant incentives to operating lease assets.
(4) As of December 31, 2018, the deferred rent balance was $1,202, which included $176 of sublease income received prior to year-end but not due until January 1, 2019.
(5) Represents recognition of operating lease liabilities.

Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2020

Investments Debt And Equity Securities [Abstract]

Summary of Cash Equivalents and Marketable Securities Recorded at Fair Value

A summary of the Company’s cash equivalents and marketable securities, which are recorded at fair value (and excludes $395.1 million of cash at December 31, 2020) is shown below (in thousands):

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	$	742,958	$	—	$	—		$	742,958
Corporate debt securities		2,526		1		(24	)		2,503
Certificates of deposit		12,527		—		—			12,527
Commercial paper		15,549		—		—			15,549
Total cash equivalents		773,560		1		(24	)		773,537
Marketable securities:
U.S. Treasury securities		47,976		3		—			47,979
Corporate debt securities		324,569		43		(156	)		324,456
Certificates of deposit		25,162		—		—			25,162
Government-sponsored enterprise securities		33,738		5		(2	)		33,741
Commercial paper		90,375		—		—			90,375
Total marketable securities		521,820		51		(158	)		521,713
Total cash equivalents and marketable securities	$	1,295,380	$	52	$	(182	)	$	1,295,250

Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of Financial Assets Measured at Fair Value on Recurring Basis

	Fair Value Measurements at
	December 31, 2020
	Total		Level 1		Level 2		Level 3
Cash and cash equivalents:
Cash	$	395,083	$	395,083	$	—	$	—
Money market funds		742,958		742,958		—		—
Corporate debt securities		2,503		—		2,503		—
Certificates of deposit		12,527		—		12,527		—
Commercial paper		15,549		—		15,549		—
Marketable securities:
U.S. Treasury securities		47,979		—		47,979		—
Corporate debt securities		324,456		—		324,456		—
Certificates of deposit		25,162		—		25,162		—
Government-sponsored enterprise securities		33,741		—		33,741		—
Commercial paper		90,375		—		90,375		—
Other non-current assets		600		—		—		600
Total	$	1,690,933	$	1,138,041	$	552,292	$	600

	Fair Value Measurements at
	December 31, 2019
	Total		Level 1		Level 2		Level 3
Cash and cash equivalents:
Cash	$	13,998	$	13,998		—		—
Money market funds		929,773		929,773		—		—
Other non-current assets		600		—		—		600
Total	$	944,371	$	943,771	$	—	$	600

Property and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2020

Property Plant And Equipment [Abstract]

Summary of Property and Equipment, Net

Property and equipment, net, consists of the following (in thousands):

	As of December 31,
	2020			2019
Computer equipment	$	727		$	727
Furniture, fixtures, and other		3,416			3,215
Laboratory equipment		25,353			16,640
Leasehold improvements		25,473			21,400
Construction work in process		8,366			1,394
Total property and equipment, gross		63,335			43,376
Accumulated Depreciation		(21,175	)		(12,046	)
Total property and equipment, net	$	42,160		$	31,330

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2020

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following (in thousands):

	As of December 31,
	2020		2019
Payroll and employee-related costs	$	22,402	$	15,229
Research costs		21,684		9,434
Licensing fees		1,401		750
Professional fees		1,670		2,040
Intellectual property costs		3,625		2,311
Accrued property and equipment		2,835		407
Other		165		9
Total	$	53,782	$	30,180

Leases (Tables)

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Summary of Lease Assets and Liabilities

The following table summarizes the lease assets and liabilities as of December 31, 2020 and 2019 (in thousands):

	As of December 31,
	2020		2019
Assets
Operating lease assets	$	50,865	$	41,502
Total lease assets		50,865		41,502
Liabilities
Current
Operating lease liabilities		11,362		8,489
Non-current
Operating lease liabilities, net of current portion		50,067		44,050
Total lease liabilities	$	61,429	$	52,539

Summary of Operating Lease Costs Included in Research and Development and General and Administrative Expense, as well as Sublease Income

	Years Ended December 31,
	2020			2019
Operating lease costs	$	14,342		$	8,067
Short-term lease costs		7,339			4,554
Variable lease costs		6,368			4,282
Sublease income		(587	)		(525	)
Net lease cost	$	27,462		$	16,378

Summary of Maturity of Undiscounted Payments Due under Lease Liabilities and Present Value of Those Liabilities

The following table summarizes the maturity of undiscounted payments due under lease liabilities and the present value of those liabilities as of December 31, 2020 (in thousands):

	Total
2021	$	17,020
2022		13,815
2023		12,650
2024		10,761
2025		10,265
Thereafter		37,206
Total	$	101,717
Present value adjustment		(40,288	)
Present value of lease liabilities	$	61,429

Summary of Lease Term and Discount Rate

The following table summarizes the lease term and discount rate as of December 31, 2020 and 2019:

	As of December 31,
	2020			2019
Weighted-average remaining lease term (years)
Operating leases		9.1			6.0
Weighted-average discount rate
Operating leases		9.3	%		9.9	%

Lessee, Operating Lease Cash Flow Payments

The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the year ended December 31, 2020 and 2019 (in thousands):

	Years Ended December 31,
	2020			2019
Cash paid for amounts included in measurement of lease liabilities:
Operating cash flows used in operating leases	$	(13,161	)	$	(8,420	)
Operating lease non-cash items:
Right-of-use assets increased through lease modifications and reassessments		3,169			826
Right-of-use assets obtained in exchange for operating lease liabilities		13,956			18,088

Significant Contracts (Tables)

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Fair Value of Assets and Liabilities Received

Fair value	Amount
Cash and cash equivalents	$	6,784
Prepaid expenses and other current assets		2,565
Property, plant and equipment, net		9,340
Operating lease assets		11,003
Restricted cash		1,226
Accrued expenses and other current liabilities		(3,915	)
Operating lease liabilities		(11,003	)
Net assets	$	16,000

Share Capital (Tables)

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Schedule of Share Capital

Share Capital consisted of the following:

		As of December 31,
Type of Share Capital	Conditional Capital	2020		2019
Common shares	Registered share capital		75,133,951		61,036,566
Common shares	Authorized share capital		17,625,426		19,246,503
Common shares	Conditional share capital - Bonds or similar debt instruments		4,919,700		4,919,700
Common shares	Conditional share capital - Employee benefit plans		17,493,709		18,698,237
	Total		115,172,786		103,901,006

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

+ References

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+ Details

Equity-based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Stock-Based Compensation Expense

Stock‑based compensation expense by classification within the consolidated statements of operations and comprehensive income (loss) is as follows (in thousands):

	Years Ended December 31,
	2020		2019		2018
Research and development	$	35,120	$	23,273	$	17,557
General and administrative		30,898		20,784		17,428
Loss from equity method investment		—		5,467		4,275
Total	$	66,018	$	49,524	$	39,260

Fair Value of Each Option Issued to Employees and Non-employees Estimated Using Black-Scholes Option-Pricing Model

The fair value of each option issued to employees and non-employees was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Years Ended December 31,
	2020			2019			2018
Options granted		2,182,773			2,832,784			2,209,597
Weighted-average exercise price	$	68.91		$	39.16		$	51.73
Weighted-average grant date fair value	$	42.28		$	24.57		$	33.82
Assumptions:
Expected volatility		69.2	%		68.9	%		71.9	%
Expected term (in years)		6.0			6.0			6.0
Risk-free interest rate		0.6	%		2.2	%		2.8	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

Summary of Stock Option Activity

The following table summarizes stock option activity under the Company’s equity award plans (intrinsic value in thousands):

	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2019		7,782,437		$	31.30		8.2	$	231,554
Granted		2,182,773		$	68.91
Exercised		(1,517,735	)	$	23.53
Cancelled or forfeited		(345,495	)	$	41.61
Outstanding at December 31, 2020		8,101,980		$	42.44		7.8		896,666
Exercisable at December 31, 2020		3,838,372		$	30.43		7.0	$	470,907
Vested and expected to vest at December 31, 2020		8,101,980		$	42.44		7.8	$	896,666

Summary of Restricted Stock Activity

The following table summarizes the restricted stock activity under the Company’s equity award plans:

	Shares			Weighted- Average Grant Date Fair Value
Unvested balance at December 31, 2019		699,534		$	56.53
Granted		437,670			77.92
Vested		(204,650	)		42.92
Cancelled or forfeited		(38,462	)		46.33
Unvested balance at December 31, 2020		894,092		$	70.55

Net Income (Loss) Per Share Attributable to Common Shareholders (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Schedule of Computation of Basic and Diluted Net (Loss) Income per Share

The following table sets forth the computation of basic and diluted net (loss) income per share for the periods ended (in thousands, except per share amounts):

	Year ended December 31,
	2020			2019		2018

Net (loss) income	$	(348,865	)	$	66,858	$	(164,981	)
Basic weighted-average common shares outstanding		65,949,672			54,392,304		47,964,368
Effect of potentially dilutive securities:
Outstanding options		—			2,406,962		—
Unvested restricted common shares		—			133,532		—
Diluted weighted-average common shares outstanding		65,949,672			56,932,798		47,964,368
Basic net (loss) income per common share	$	(5.29	)	$	1.23	$	(3.44	)
Diluted net (loss) income per common share	$	(5.29	)	$	1.17	$	(3.44	)

Schedule of Antidilutive Securities not Include in Computation of Net (Loss) Income per Share

	Year ended December 31,
	2020		2019		2018
Outstanding options		8,101,980		3,789,129		6,689,311
Unvested restricted common shares		894,092		108,625		327,342
ESPP		11,257		—		—
Total		9,007,329		3,897,754		7,016,653

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of (Loss) Income Before Provision for Income Taxes

For the years ended December 31, 2020, 2019 and 2018, the (loss) income before provision for income taxes consist of the following (in thousands):

	Years Ended December 31,
	2020			2019		2018
Domestic	$	7,630		$	9,155	$	5,966
Foreign		(355,686	)		58,151		(170,394	)
Total	$	(348,056	)	$	67,306	$	(164,428	)

Schedule of (Provision for) Benefit from Income Taxes

The (provision for) benefit from income taxes consist of the following (in thousands):

	Years Ended December 31,
	2020			2019			2018
Current income taxes:
Federal	$	(248	)	$	(423	)	$	(416	)
State		(151	)		(59	)		(131	)
Foreign		(1	)		0			0
Total current income taxes		(400	)		(482	)		(547	)
Deferred income taxes:
Federal		(409	)		34			(6	)
State		—			—			—
Foreign		—			—			—
Total deferred income taxes		(409	)		34			(6	)
Total income tax (provision) benefit	$	(809	)	$	(448	)	$	(553	)

Schedule of Reconciliation of Income Tax Expense Computed at Statutory Corporate Income Tax Rate to Effective Income Tax Rate

A reconciliation of income tax expense computed at the statutory corporate income tax rate to the effective income tax rate for the years ended December 31, 2020, 2019 and 2018 is as follows:

	Years Ended December 31,
	2020			2019			2018
Income tax expense at statutory rate		11.9	%		9.3	%		9.3	%
State income tax, net of federal benefit		1.0	%		(2.1	)%		0.7	%
Nondeductible expenses		0.1	%		(0.1	)%		0.0	%
Foreign rate differential		(0.1	)%		2.0	%		(0.4	)%
Statutory to US GAAP permanent differences		0.0	%		0.1	%		1.0	%
Stock-based compensation		2.3	%		(2.0	)%		1.4	%
Impact of deferred rate change		0.0	%		(12.2	)%		0.0	%
Research credits		3.3	%		(5.2	)%		1.8	%
Change in valuation allowance		(18.7	)%		10.9	%		(14.1	)%
Effective income tax rate		(0.2	%)		0.7	%		(0.3	%)

Schedule of Significant Components of Company's Deferred Tax Assets

	Years Ended December 31,
	2020			2019
Deferred tax assets:
Net operating loss carryforwards	$	84,531		$	31,496
Accruals and reserves		4,785			2,868
Operating lease liabilities		16,782			14,214
Other deferred tax assets		1,517			28
Stock-based compensation		9,605			5,217
Deferred revenue		86			(20	)
Research credit		19,526			7,150
Total deferred tax assets		136,832			60,953
Less valuation allowance		(116,640	)		(45,913	)
Net deferred tax assets		20,192			15,040
Deferred tax liabilities:
Depreciation		(6,778	)		(3,901	)
Operating lease assets		(13,776	)		(11,068	)
Intangible assets		(31	)		(40	)
Other deferred tax liabilities		(4	)		(20	)
Total deferred tax liabilities		(20,589	)		(15,029	)
Long term deferred taxes	$	(397	)	$	11

Schedule of Aggregate Changes in Gross Unrecognized Tax Benefits

The aggregate changes in gross unrecognized tax benefits were as follows (in thousands):

	Years Ended December 31,
	2020			2019		2018
Balance at beginning of year	$	5,231		$	1,595	$	354
Increases for tax positions taken during current period		7,004			2,754		1,212
Increases for tax positions taken in prior periods		—			882		29
Decreases for tax positions taken during current period		—			—		—
Decreases for tax positions taken in prior periods		(268	)		—		—
Balance at end of year	$	11,967		$	5,231	$	1,595

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2020

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data

The following table sets forth the Company’s quarterly financial data for the two years ended December 31, 2020.

	2020
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Total revenue	$	157		$	44		$	148		$	370
Total operating expenses		73,743			80,733			92,547			108,131
Loss from operations		(73,586	)		(80,689	)		(92,399	)		(107,761	)
Net loss		(69,731	)		(79,656	)		(92,439	)		(107,039	)
Net loss per common share:
Basic	$	(1.15	)	$	(1.30	)	$	(1.32	)	$	(1.50	)
Diluted	$	(1.15	)	$	(1.30	)	$	(1.32	)	$	(1.50	)
Weighted-average common shares outstanding:
Basic		60,847,683			61,420,746			70,143,481			71,282,096
Diluted		60,847,683			61,420,746			70,143,481			71,282,096

	2019
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Total revenue	$	328		$	318		$	211,928		$	77,016
Total operating expenses		48,751			55,301			72,765			66,033
Loss from operations		(48,423	)		(54,983	)		139,163			10,983
Net (loss) income		(48,408	)		(53,699	)		138,423			30,542
Net (loss) income per common share:
Basic	$	(0.93	)	$	(1.01	)	$	2.52		$	0.53
Diluted	$	(0.93	)	$	(1.01	)	$	2.40		$	0.51
Weighted-average common shares outstanding:
Basic		52,093,208			53,188,041			54,829,057			57,395,839
Diluted		52,093,208			53,188,041			57,598,901			60,233,927

Organization and Operations - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Company incorporation date									Oct. 31, 2013
Accumulated deficit	$ (573,576)				$ (224,711)				$ (573,576)	$ (224,711)
Cash, cash equivalents and marketable securities	1,690,300								1,690,300
Net (loss) income	$ (107,039)	$ (92,439)	$ (79,656)	$ (69,731)	$ 30,542	$ 138,423	$ (53,699)	$ (48,408)	$ (348,865)	$ 66,858	$ (164,981)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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+ Details

Summary of Significant Accounting Policies and Basis of Presentation - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Dec. 12, 2019	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2016	Feb. 12, 2016
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments \| Segment	1
Cash and cash equivalents	$ 1,168,620,000	$ 943,771,000			$ 456,649,000
Restricted Cash	16,848,000	5,041,000			3,163,000
Marketable securities	521,713,000	0.0
Contract assets	300,000	25,700,000
Contract liabilities	12,200,000	12,700,000
Deferred revenue	1,900,000	0
Net lease assets	50,865,000	41,502,000
Net lease liabilities	61,429,000	52,539,000
Significant uncertain tax positions	0	0			$ 0
Vertex and Casebia [Member] \| Collaborative Arrangement [Member]
Summary Of Significant Accounting Policies [Line Items]
Other receivables	$ 10,700,000	$ 4,100,000
ASC 326 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect	true
ASC 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2018
Change in accounting principle, accounting standards update, immaterial effect	true
ASC 842 [Member]
Summary Of Significant Accounting Policies [Line Items]
Net lease assets				$ 26,087,000
Net lease liabilities				$ 37,600,000
Casebia Therapeutics Limited Liability Partnership [Member]
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage			50.00%			50.00%	50.00%

Summary of Significant Accounting Policies and Basis of Presentation - Schedule of Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 2020
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	3 years
Furniture, Fixtures, and Other [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	5 years
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	5 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Leasehold improvements	Shorter of useful life or remaining lease term

Summary of Significant Accounting Policies and Basis of Presentation - Impact of Adopting ASC 842 on Financial Statements (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Prepaid expenses and other current assets	$ 26,143	$ 43,677
Operating lease assets	50,865	41,502
Deferred rent				$ 1,202
Operating lease liabilities	11,362	8,489
Non-current operating lease liabilities	$ 50,067	$ 44,050
ASC 842 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Prepaid expenses and other current assets			$ 9,105
Operating lease assets			26,087
Operating lease liabilities			4,930
Non-current operating lease liabilities			32,682
Prior [Member] \| ASC 842 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Prepaid expenses and other current assets			9,658
Deferred rent			1,026
Deferred rent non-current			11,052
Adjustment [Member] \| ASC 842 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Prepaid expenses and other current assets			(553)
Operating lease assets			26,087
Deferred rent			(1,026)
Deferred rent non-current			(11,052)
Operating lease liabilities			4,930
Non-current operating lease liabilities			$ 32,682

Summary of Significant Accounting Policies and Basis of Presentation - Impact of Adopting ASC 842 on Financial Statements (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Deferred rent			$ 1,202
Sublease income	$ 587	$ 525	$ 176

Marketable Securities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Marketable securities	$ 395,100,000	$ 0
Marketable securities unrealized loss, Less than twelve months	280,300,000
Marketable securities unrealized loss, more than twelve months	0
Unrealized loss, net	100,000
Marketable securities remaining maturities greater than two years	$ 0

Marketable Securities - Summary of Cash Equivalents and Marketable Securities Recorded at Fair Value (Detail) $ in Thousands	Dec. 31, 2020 USD ($)
Marketable Securities [Line Items]
Cash equivalents, amortized cost	$ 773,560
Cash equivalents, gross unrealized gains	1
Cash equivalents, gross unrealized losses	(24)
Cash equivalents, fair value	773,537
Marketable securities, amortized cost	521,820
Marketable securities, gross unrealized gains	51
Marketable securities, gross unrealized losses	(158)
Marketable securities, fair value	521,713
Cash equivalents and marketable securities, amortized cost	1,295,380
Cash equivalents and marketable securities, gross unrealized gains	52
Cash equivalents and marketable securities, gross unrealized losses	(182)
Cash equivalents and marketable securities, fair value	1,295,250
Money Market Funds [Member]
Marketable Securities [Line Items]
Cash equivalents, amortized cost	742,958
Cash equivalents, fair value	742,958
Certificates of Deposit [Member]
Marketable Securities [Line Items]
Cash equivalents, amortized cost	12,527
Cash equivalents, fair value	12,527
Marketable securities, amortized cost	25,162
Marketable securities, fair value	25,162
Commercial Paper [Member]
Marketable Securities [Line Items]
Cash equivalents, amortized cost	15,549
Cash equivalents, fair value	15,549
Marketable securities, amortized cost	90,375
Marketable securities, fair value	90,375
US Treasury Securities [Member]
Marketable Securities [Line Items]
Marketable securities, amortized cost	47,976
Marketable securities, gross unrealized gains	3
Marketable securities, fair value	47,979
Corporate Debt Securities [Member]
Marketable Securities [Line Items]
Cash equivalents, amortized cost	2,526
Cash equivalents, gross unrealized gains	1
Cash equivalents, gross unrealized losses	(24)
Cash equivalents, fair value	2,503
Marketable securities, amortized cost	324,569
Marketable securities, gross unrealized gains	43
Marketable securities, gross unrealized losses	(156)
Marketable securities, fair value	324,456
Government-sponsored Enterprise Securities [Member]
Marketable Securities [Line Items]
Marketable securities, amortized cost	33,738
Marketable securities, gross unrealized gains	5
Marketable securities, gross unrealized losses	(2)
Marketable securities, fair value	$ 33,741

Fair Value Measurement - Schedule of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 6,784
Marketable securities, fair value	521,713
Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other non-current assets	600	$ 600
Total	1,690,933	944,371
Recurring Basis [Member] \| Cash [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	395,083	13,998
Recurring Basis [Member] \| Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	742,958	929,773
Recurring Basis [Member] \| Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	2,503
Marketable securities, fair value	324,456
Recurring Basis [Member] \| Certificates of Deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	12,527
Marketable securities, fair value	25,162
Recurring Basis [Member] \| Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	15,549
Marketable securities, fair value	90,375
Recurring Basis [Member] \| US Treasury Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, fair value	47,979
Recurring Basis [Member] \| Government-sponsored Enterprise Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, fair value	33,741
Recurring Basis [Member] \| Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	1,138,041	943,771
Recurring Basis [Member] \| Level 1 [Member] \| Cash [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	395,083	13,998
Recurring Basis [Member] \| Level 1 [Member] \| Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	742,958	929,773
Recurring Basis [Member] \| Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	552,292
Recurring Basis [Member] \| Level 2 [Member] \| Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	2,503
Marketable securities, fair value	324,456
Recurring Basis [Member] \| Level 2 [Member] \| Certificates of Deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	12,527
Marketable securities, fair value	25,162
Recurring Basis [Member] \| Level 2 [Member] \| Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	15,549
Marketable securities, fair value	90,375
Recurring Basis [Member] \| Level 2 [Member] \| US Treasury Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, fair value	47,979
Recurring Basis [Member] \| Level 2 [Member] \| Government-sponsored Enterprise Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, fair value	33,741
Recurring Basis [Member] \| Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other non-current assets	600	600
Total	$ 600	$ 600

Property and Equipment, net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 63,335	$ 43,376
Accumulated Depreciation	(21,175)	(12,046)
Total property and equipment, net	42,160	31,330
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	727	727
Furniture, Fixtures, and Other [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	3,416	3,215
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	25,353	16,640
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	25,473	21,400
Construction Work in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 8,366	$ 1,394

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Depreciation expense	$ 9.1	$ 4.7	$ 3.5

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accrued Liabilities Current [Abstract]
Payroll and employee-related costs	$ 22,402	$ 15,229
Research costs	21,684	9,434
Licensing fees	1,401	750
Professional fees	1,670	2,040
Intellectual property costs	3,625	2,311
Accrued property and equipment	2,835	407
Other	165	9
Total	$ 53,782	$ 30,180

Leases - Additional Information (Detail) $ in Millions	1 Months Ended							12 Months Ended
Leases - Additional Information (Detail) $ in Millions	Jul. 31, 2020 USD ($)	May 31, 2020 Term	Dec. 31, 2019	Nov. 30, 2019 USD ($)	May 31, 2019	May 31, 2016	Jun. 30, 2015	Dec. 31, 2020
2015 Lease [Member]
Lessee Lease Description [Line Items]
Lease commencement date							Nov. 15, 2015
Lessee, operating lease, existence of option to extend							false
Lessee, operating lease, option to extend								expires in September 2022 with no further option to extend
Lease expiration, month and year							2022-09
2016 Sublease [Member]
Lessee Lease Description [Line Items]
Lease commencement date						Dec. 23, 2016
Lease expiration, month and year						2026-12
Lessee, operating sublease, option to extend								an option to extend the term of the sublease for an additional five-year period if, at the time of expiration of the initial term
Lessee, operating sublease, existence of option to extend						true
Extended term of lease expiration						5 years
2019 Lease [Member]
Lessee Lease Description [Line Items]
Lease commencement date					Jun. 01, 2019
Lessee, operating lease, existence of option to extend					true
Lessee, operating lease, option to extend								an option to extend the term of the lease for an additional five-year period based on certain conditions within the Company’s control.
Lease expiration, month and year					2026-11
Extended term of lease expiration					5 years
2019 Sublease [Member]
Lessee Lease Description [Line Items]
Lease expiration, month and year			2024-03
Lessee, operating sublease, option to extend								an option to extend the term of the sublease for an additional five-year period if, at the time of expiration of the initial term
Lessee, operating sublease, existence of option to extend			true
Extended term of lease expiration			5 years
Framingham Lease [Member]
Lessee Lease Description [Line Items]
Lease expiration, month and year		2036-03
Lessee, operating sublease, existence of option to extend		true
Number of additional renewal terms \| Term		2
Lease renewal term under each extension option		7 years
2020 Boston Lease [Member]
Lessee Lease Description [Line Items]
Annual rental payments	$ 292.5
Rental payments period	152 months
Lease Arrangement
Lessee Lease Description [Line Items]
Annual rental payments				$ 3.8
Rental payments period				5 years

Leases - Summary of Lease Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
Operating lease assets	$ 50,865	$ 41,502
Total lease assets	50,865	41,502
Liabilities
Operating lease liabilities, current	11,362	8,489
Operating lease liabilities, net of current portion	50,067	44,050
Total lease liabilities	$ 61,429	$ 52,539

Leases - Summary of Operating Lease Costs Included in Research and Development and General and Administrative Expense, as well as Sublease Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease costs	$ 14,342	$ 8,067
Short-term lease costs	7,339	4,554
Variable lease costs	6,368	4,282
Sublease income	(587)	(525)	$ (176)
Net lease cost	$ 27,462	$ 16,378

Leases - Summary of Maturity of Undiscounted Payments Due under Lease Liabilities and Present Value of Those Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2021	$ 17,020
2022	13,815
2023	12,650
2024	10,761
2025	10,265
Thereafter	37,206
Total	101,717
Present value adjustment	(40,288)
Present value of lease liabilities	$ 61,429	$ 52,539

Leases - Summary of Lease Term and Discount Rate (Detail)	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating leases, weighted-average remaining lease term (years)	9 years 1 month 6 days	6 years
Operating leases, weighted-average discount rate	9.30%	9.90%

Leases - Summary of Cash Paid for Amounts Included in Measurement of Lease Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in measurement of lease liabilities:
Operating cash flows used in operating leases	$ (13,161)	$ (8,420)
Operating lease non-cash items:
Right-of-use assets increased through lease modifications and reassessments	3,169	826
Right-of-use assets obtained in exchange for operating lease liabilities	$ 13,956	$ 18,088

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Contingencies And Commitments [Line Items]
Cost sharing expensed relating to patent maintenance, defense and prosecution, incurred	$ 4.5	$ 2.9	$ 2.4
Cost sharing expensed relating to patent maintenance, defense and prosecution, accrued	2.5	$ 1.5
2015 Collaboration Agreement [Member] \| Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member]
Contingencies And Commitments [Line Items]
Milestone payment receivable	$ 395.0

Significant Contracts - Additional Information (Detail)

1 Months Ended

2 Months Ended

3 Months Ended

12 Months Ended

Dec. 13, 2019

USD ($)

Product

Dec. 18, 2018

USD ($)

Nov. 15, 2018

USD ($)

Sep. 24, 2018

USD ($)

Sep. 17, 2018

USD ($)

Installment

Oct. 26, 2015

USD ($)

Dec. 31, 2019

USD ($)

Oct. 31, 2019

License

Dec. 18, 2018

USD ($)

Nov. 14, 2018

USD ($)

Dec. 31, 2020

USD ($)

Sep. 30, 2020

USD ($)

Jun. 30, 2020

USD ($)

Mar. 31, 2020

USD ($)

Dec. 31, 2019

USD ($)

Sep. 30, 2019

USD ($)

Jun. 30, 2019

USD ($)

Mar. 31, 2019

USD ($)

Dec. 31, 2020

USD ($)

Option

Dec. 31, 2019

USD ($)

Dec. 31, 2018

USD ($)

Apr. 30, 2020

USD ($)

Dec. 12, 2019

Mar. 31, 2016

Feb. 12, 2016

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Non-current deferred revenue

$ 11,776,000

Current deferred revenue

960,000

2,341,000

960,000

2,341,000

960,000

Research and development expense

^[1]

$ 266,946,000

179,362,000

$ 113,773,000

Date of joint venture agreement

Dec. 19, 2015

Operating expenses

108,131,000

$ 92,547,000

$ 80,733,000

$ 73,743,000

66,033,000

$ 72,765,000

$ 55,301,000

$ 48,751,000

$ 355,154,000

242,850,000

162,067,000

Stock-based compensation expense

66,018,000

49,524,000

39,260,000

Net loss of joint venture

(348,865,000)

66,858,000

(164,981,000)

Issuance of common shares, value

973,381,000

414,789,000

307,053,000

Net proceeds from issuance of common shares

982,289,000

415,019,000

307,053,000

Other (expense) income

$ 6,379,000

26,033,000

(1,210,000)

Casebia Therapeutics Limited Liability Partnership [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Research and development expense

700,000

3,800,000

Reimbursements from research and license agreements

200,000

900,000

Date of formation of joint venture entity

Feb. 12, 2016

Equity method investment, ownership percentage

50.00%

Stock-based compensation expense

5,500,000

4,300,000

Unrecognized equity method losses in excess of Company's interest

72,000,000.0

Business combination, consideration transferred

$ 41,000,000.0

Net assets acquired

$ 16,000,000.0

16,000,000.0

Fair value of controlling interest obtained

32,000,000.0

Casebia Therapeutics Limited Liability Partnership [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Net loss of joint venture

$ 58,800,000

52,500,000

Research and Development [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Stock-based compensation expense

$ 35,120,000

23,273,000

17,557,000

License and Service [Member] | Casebia Therapeutics Limited Liability Partnership [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Collaboration revenue

500,000

2,500,000

Non-Exclusive Research License [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Transaction price allocated to remaining performance obligations

$ 500,000

Non-Exclusive Research License [Member] | Valuation, Market Approach

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for collaboration agreement

1,000,000.0

Retirement Agreement [Member] | Casebia Therapeutics Limited Liability Partnership [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Percentage of partnership interests

100.00%

Partnership outstanding maximum exchange amount

$ 22,000,000.0

Operating expenses

$ 6,000,000.0

2019 Option Agreement [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Research and development expense

13,200,000

2019 Option Agreement [Member] | Casebia Therapeutics Limited Liability Partnership [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Equity method investment, ownership percentage

50.00%

Number of products | Product

Non-refundable one-time option payment

$ 20,000,000.0

Business combination, consideration transferred

$ 25,000,000.0

Payment to acquire business

$ 16,000,000.0

Number of options exercised under agreement | Option

2019 Option Agreement [Member] | Research and Development [Member] | Casebia Therapeutics Limited Liability Partnership [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Business combination, consideration transferred

$ 20,200,000

2019 Option Agreement [Member] | Certain Options [Member] | Casebia Therapeutics Limited Liability Partnership [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Business combination, consideration transferred

4,800,000

2019 Option Agreement [Member] | Research and Development Services [Member] | Casebia Therapeutics Limited Liability Partnership [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Fair value of obligations

$ 20,200,000

20,200,000

2019 Option Agreement [Member] | Future Delivery of up to Two Options [Member] | Casebia Therapeutics Limited Liability Partnership [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Fair value of obligations

4,800,000

Co-commercialization Agreement [Member] | Casebia Therapeutics Limited Liability Partnership [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Percentage of research and development costs

50.00%

Percentage sharing of profit (loss) from sale of product

50.00%

2015 Casebia Agreement [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Equity method investment

2019 Casebia Agreement [Member] | Other Current Liabilities [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Research obligation

7,000,000.0

2019 Casebia Agreement [Member] | Other Long-term Liabilities [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Research obligation

$ 4,800,000

4,800,000

2019 Casebia Agreement [Member] | Casebia Therapeutics Limited Liability Partnership [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Equity method investment

Fair value of assets and liabilities

16,000,000.0

Research Collaboration Agreement [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Cost sharing percentage on specified costs

60.00%

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Nonrefundable upfront payment received

75,000,000.0

175,000,000.0

Transaction price

268,600,000

Non-current deferred revenue

$ 11,800,000

11,800,000

Non-cash consideration received

10,000,000.0

Transaction price allocated to remaining performance obligations

11,900,000

Revenue

500,000

289,100,000

Current deferred revenue

$ 900,000

400,000

900,000

400,000

900,000

Collaboration revenue

30,000,000.0

Maximum potential future payments

800,000,000

Research and development expense

48,600,000

29,200,000

20,200,000

Reimbursements from research and license agreements

28,200,000

15,900,000

13,800,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Research and Development [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Variable consideration received

19,300,000

25,000,000.0

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Collaboration Target Options [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Milestone payment receivable

420,000,000.0

Milestone payment receivable

410,000,000.0

Transaction price allocated to remaining performance obligations

46,700,000

Revenue

76,700,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | DM1 R&D Services [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

1,700,000

Transaction price allocated to remaining performance obligations

1,100,000

Revenue

100,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | DM1 R&D Services [Member] | Research and Development [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Variable consideration received

800,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | DMD License [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

224,600,000

Transaction price allocated to remaining performance obligations

151,100,000

Revenue

289,100,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | DM1 License [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

76,200,000

Transaction price allocated to remaining performance obligations

51,300,000

Revenue

202,400,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Specified Target Option Material Right [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

17,500,000

Transaction price allocated to remaining performance obligations

11,800,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Collaboration Target Options Material Rights One [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

25,000,000.0

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Collaboration Target Options Material Rights Two [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

22,200,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Collaboration Target Options Material Rights Three [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

22,200,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Waiving of Vertex?s Material Right [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Revenue

6,700,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Joint Development Agreement [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Up-front payment received

7,000,000.0

$ 7,000,000.0

Agreement description

In connection with the JDA, the Company received a $7.0 million up-front payment from Vertex and subsequently received a one-time low seven-digit milestone payment upon the dosing of the second patient in a clinical trial with the initial product candidate.

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Exercise of Exclusive Option [Member] | Collaboration Target Options [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Milestone payment receivable

10,000,000

$ 10,000,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | 2019 Collaboration Agreement [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Nonrefundable upfront payment received

175,000,000.0

Maximum potential payments

825,000,000

$ 825,000,000

Percentage of exchange payment of research and development costs

50.00%

Collaborative arrangement, license rights reacquired by waiving payment owed

$ 10,000,000.0

Non-cash consideration expensed upon execution of collaborative agreement

10,000,000.0

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | 2015 Collaboration Agreement [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Milestone payment receivable

395,000,000.0

$ 395,000,000.0

Percentage of exchange payment of research and development costs

50.00%

Number of options would not be exercised under agreement | Option

Number of remaining options under agreement | Option

Non-current deferred revenue

57,800,000

$ 57,800,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | 2015 Collaboration Agreement [Member] | Collaborative Arrangement Material Rights Fourth Exclusive License [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

10,000,000.0

Transaction price allocated to remaining performance obligations

$ 6,700,000

Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Non-Exclusive Research License [Member] | Research and Development Services [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Revenue

$ 100,000

600,000

Vertex Pharmaceuticals Inc [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

19,300,000

Transaction price allocated to remaining performance obligations

19,300,000

Estimated standalone selling price for collaboration agreement

118,600,000

Vertex Pharmaceuticals Inc [Member] | Collaboration Target Options [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Transaction price allocated to remaining performance obligations

57,700,000

Vertex Pharmaceuticals Inc [Member] | Collaboration Target Options Material Rights One [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

45,600,000

Vertex Pharmaceuticals Inc [Member] | Collaboration Target Options Material Rights Two [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

38,400,000

Vertex Pharmaceuticals Inc [Member] | Collaboration Target Options Material Rights Three [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

17,300,000

Vertex Pharmaceuticals Inc [Member] | Rights Four [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

17,300,000

Vertex Pharmaceuticals Inc [Member] | 2019 Collaboration Agreement [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Milestone payment receivable

$ 25,000,000.0

Vertex Pharmaceuticals Inc [Member] | 2015 Collaboration Agreement [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Aggregate amount in option exercise payments received

$ 30,000,000.0

Number of exclusive license targets | License

Vertex Pharmaceuticals Inc [Member] | Beta Globin

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Estimated standalone selling price for single collaboration

48,900,000

Transaction price allocated to remaining performance obligations

$ 23,800,000

ViaCyte [Member] | Research Collaboration Agreement [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Research and development expense

15,000,000.0

Amount payable under collaboration agreement

$ 15,000,000.0

Number of installments for amount payable | Installment

Issuance of common shares | shares

214,512

165,636

Issuance of common shares, value

$ 8,100,000

$ 7,500,000

Key provisions of collaborative agreement description

The agreement includes certain provisions such that in the event ViaCyte sold shares received from the Company for less than $15.0 million in combined net proceeds, the Company would owe ViaCyte the deficient amount. In the event ViaCyte sold shares received from the Company for greater than $15.0 million in combined net proceeds, ViaCyte would owe the Company the surplus amount.

Net proceeds from issuance of common shares

$ 7,500,000

$ 6,900,000

Deficient amount payable

$ 600,000

Deficient amount paid in cash

$ 600,000

Total consideration paid

16,200,000

Other (expense) income

$ (1,200,000)

Collaboration agreement period

6 years

Cost sharing percentage on specified costs

40.00%

ViaCyte [Member] | Research Collaboration Agreement [Member] | Convertible Promissory Note [Member]

Research and Development Arrangement, Contract to Perform for Others [Line Items]

Additional amount payable under certain circumstances

$ 10,000,000.0

[1]	Including the following amounts of research and development from a related party, see Note 9

Significant Contracts - Schedule of Fair Value of Assets and Liabilities Received (Detail) $ in Thousands	Dec. 31, 2020 USD ($)
Research And Development [Abstract]
Cash and cash equivalents	$ 6,784
Prepaid expenses and other current assets	2,565
Property, plant and equipment, net	9,340
Operating lease assets	11,003
Restricted cash	1,226
Accrued expenses and other current liabilities	(3,915)
Operating lease liabilities	(11,003)
Net assets	$ 16,000

Share Capital - Additional Information (Detail)		1 Months Ended								12 Months Ended
Share Capital - Additional Information (Detail)	Feb. 16, 2021 USD ($) $ / shares shares	Jan. 31, 2021 USD ($) $ / shares shares	Jul. 31, 2020 USD ($) $ / shares shares	Nov. 30, 2019 USD ($) $ / shares shares	Aug. 31, 2019 USD ($)	Sep. 30, 2018 USD ($) $ / shares shares	Aug. 31, 2018 USD ($)	Jan. 31, 2018 USD ($) $ / shares shares	Oct. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)	Dec. 31, 2020 SFr / shares	Dec. 31, 2019 SFr / shares	Aug. 31, 2019 SFr / shares
Class of Stock [Line Items]
Common stock, shares authorized \| shares										115,172,786	103,901,006
Common shares, par value \| SFr / shares													SFr 0.03	SFr 0.03
Capital reserved for future issuance \| shares										2,906,383
Proceeds from issuance of common shares										$ 982,289,000	$ 415,019,000	$ 307,053,000
Common Stock, Voting Rights										one vote for each Common Share
Dividends declared and paid										$ 0
IPO [Member]
Class of Stock [Line Items]
Common shares sold \| shares									4,400,000
Common shares price per share \| $ / shares									$ 14.00
Proceeds from issuance of common shares									$ 53,700,000
Equity issuance costs									$ 8,300,000
Private Placement [Member] \| Bayer Global Investments B.V [Member]
Class of Stock [Line Items]
Common shares sold \| shares									2,500,000
Common shares price per share \| $ / shares									$ 14.00
Proceeds from issuance of common shares									$ 35,000,000.0
Underwritten Public Offering [Member]
Class of Stock [Line Items]
Common shares sold \| shares			7,400,000	4,900,000		4,200,000		5,700,000
Common shares price per share \| $ / shares			$ 70.00	$ 64.50		$ 47.50		$ 22.75
Proceeds from issuance of common shares			$ 489,700,000	$ 297,400,000		$ 184,500,000		$ 122,600,000
Equity issuance costs			$ 27,600,000	$ 17,800,000		$ 12,400,000		$ 8,200,000
Payments of stamp taxes related to securities											$ 3,000,000.0	$ 3,100,000
Additional equity issuance costs of stamp taxes										4,900,000
Payable of stamp taxes related to securities										4,900,000
2018 ATM [Member] \| Sales Agreement With Jefferies LLC [Member]
Class of Stock [Line Items]
Common shares sold \| shares											2,800,000
Proceeds from issuance of common shares											$ 120,600,000
Equity issuance costs											4,400,000
Payments of stamp taxes related to securities										$ 300,000	$ 900,000
Average issue price of common shares \| $ / shares											$ 44.38
Accrued stamp taxes											$ 300,000
2018 ATM [Member] \| Sales Agreement With Jefferies LLC [Member] \| Maximum [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds							$ 125,000,000.0
2019 ATM [Member] \| Sales Agreement With Jefferies LLC [Member]
Class of Stock [Line Items]
Common shares, par value \| SFr / shares															SFr 0.03
Common shares sold \| shares										2,200,000
Proceeds from issuance of common shares										$ 195,500,000
Equity issuance costs										$ 4,500,000
Average issue price of common shares \| $ / shares										$ 89.47
2019 ATM [Member] \| Sales Agreement With Jefferies LLC [Member] \| Maximum [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds					$ 200,000,000.0
2020 ATM [Member] \| Sales Agreement With Jefferies LLC [Member]
Class of Stock [Line Items]
Common shares sold \| shares										1,800,000
Proceeds from issuance of common shares										$ 298,000,000.0
Equity issuance costs										4,500,000
Payments of stamp taxes related to securities										4,900,000
Payable of stamp taxes related to securities										$ 4,000,000.0
Average issue price of common shares \| $ / shares										$ 169.57
2020 ATM [Member] \| Sales Agreement With Jefferies LLC [Member] \| Subsequent Event [Member]
Class of Stock [Line Items]
Common shares sold \| shares		300,000
Equity issuance costs		$ 700,000
Payments of stamp taxes related to securities		500,000
Aggregate estimated gross proceeds		$ 46,700,000
Average issue price of common shares \| $ / shares		$ 162.46
2020 ATM [Member] \| Sales Agreement With Jefferies LLC [Member] \| Maximum [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds					$ 350,000,000.0
2021 ATM [Member] \| Sales Agreement With Jefferies LLC [Member] \| Subsequent Event [Member]
Class of Stock [Line Items]
Common shares sold \| shares	1,100,000
Equity issuance costs	$ 2,400,000
Payments of stamp taxes related to securities	1,800,000
Aggregate estimated gross proceeds	$ 177,800,000
Average issue price of common shares \| $ / shares	$ 169.82
2021 ATM [Member] \| Sales Agreement With Jefferies LLC [Member] \| Maximum [Member] \| Subsequent Event [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds		$ 600,000,000.0

Share Capital - Schedule of Share Capital (Detail) - shares	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Registered share capital	75,133,951	61,036,566
Authorized share capital	115,172,786	103,901,006
Employee Benefit Plans [Member]
Class of Stock [Line Items]
Conditional share capital - Bonds or similar debt instruments	17,493,709	18,698,237
Bonds or Similar Debt Instruments [Member]
Class of Stock [Line Items]
Conditional share capital - Bonds or similar debt instruments	4,919,700	4,919,700
Swiss Law [Member]
Class of Stock [Line Items]
Authorized share capital	17,625,426	19,246,503

Equity-based Compensation - Option and Grant Plans - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment award, number of shares granted	2,182,773	2,832,784	2,209,597
Minimum [Member] \| Restricted Stock Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, vesting period	2 years
Maximum [Member] \| Restricted Stock Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, vesting period	3 years
Option and Grant Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, vesting period	4 years
Share-based compensation, options, contractual life	10 years
Option and Grant Plans [Member] \| IPO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment award, number of shares granted	0

Equity-based Compensation - Equity-Based Compensation Expense - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 66,018	$ 49,524	$ 39,260
Total unrecognized compensation expense related to stock options	132,500
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 45,700
Unrecognized compensation expense, remaining weighted-average period for recognition	2 years 1 month 6 days
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, remaining weighted-average period for recognition	2 years 9 months 18 days

Equity-based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 66,018	$ 49,524	$ 39,260
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	35,120	23,273	17,557
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 30,898	20,784	17,428
Loss from Equity Method Investment [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense		$ 5,467	$ 4,275

Equity-based Compensation - Fair Value of Each Option Issued to Employees and Non-employees Estimated Using Black-Scholes Option-Pricing Model (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options granted	2,182,773	2,832,784	2,209,597
Weighted-average exercise price	$ 68.91	$ 39.16	$ 51.73
Weighted-average grant date fair value	$ 42.28	$ 24.57	$ 33.82
Expected volatility	69.20%	68.90%	71.90%
Expected term (in years)	6 years	6 years	6 years
Risk-free interest rate	0.60%	2.20%	2.80%
Expected dividend yield	0.00%	0.00%	0.00%

Equity-based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]
Shares, Outstanding, Beginning Balance	7,782,437
Shares, Granted	2,182,773	2,832,784	2,209,597
Shares, Exercised	(1,517,735)
Shares, Cancelled or forfeited	(345,495)
Shares, Outstanding, Ending Balance	8,101,980	7,782,437
Shares, Exercisable	3,838,372
Shares, Vested or expected to vest	8,101,980
Weighted-Average Exercise Price, Outstanding, Beginning Balance	$ 31.30
Weighted-Average Exercise Price, Granted	68.91	$ 39.16	$ 51.73
Weighted-Average Exercise Price, Exercised	23.53
Weighted-Average Exercise Price, Cancelled or forfeited	41.61
Weighted-Average Exercise Price, Outstanding, Ending Balance	42.44	$ 31.30
Weighted-Average Exercise Price, Exercisable	30.43
Weighted-Average Exercise Price, Vested or expected to vest	$ 42.44
Weighted-Average Remaining Contractual Term	7 years 9 months 18 days	8 years 2 months 12 days
Weighted-Average Remaining Contractual Term, Exercisable	7 years
Weighted-Average Remaining Contractual Term, Vested or expected to vest	7 years 9 months 18 days
Aggregate Intrinsic Value, Outstanding Balance	$ 896,666	$ 231,554
Aggregate Intrinsic Value, Exercisable	470,907
Aggregate Intrinsic Value, Vested or expected to vest	$ 896,666

Equity-based Compensation - Stock Options - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, options, outstanding	8,101,980	7,782,437
Stock Options, Granted	2,182,773	2,832,784	2,209,597
Total intrinsic value of stock options exercised	$ 104.2	$ 42.2	$ 38.3
Performance-Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options, Granted	0	0
Performance-Based [Member] \| Vesting Percentage on First Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, options, vested	940,646
Share-based compensation, options, outstanding	81,387
Market-Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, options, vested	112,500
Stock Options, Granted	0	0		150,000
Market-Based [Member] \| Vesting Percentage on First Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, requisite service period				3 years
Share-based compensation, vesting percentage				75.00%
Market-Based [Member] \| Vesting Percentage on Second Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, requisite service period				4 years
Share-based compensation, vesting percentage				25.00%

Equity-based Compensation - Summary of Restricted Stock Activity (Detail) - Restricted Stock [Member]	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, Shares, Beginning Balance \| shares	699,534
Unvested, Shares, Granted \| shares	437,670
Unvested, Shares, Vested \| shares	(204,650)
Unvested, Shares, Cancelled or forfeited \| shares	(38,462)
Unvested, Shares, Ending Balance \| shares	894,092
Unvested, Weighted-Average Grant Date Fair Value, Beginning Balance \| $ / shares	$ 56.53
Unvested, Weighted-Average Grant Date Fair Value, Granted \| $ / shares	77.92
Unvested, Weighted-Average Grant Date Fair Value, Vested \| $ / shares	42.92
Unvested, Weighted-Average Grant Date Fair Value, Cancelled or forfeited \| $ / shares	46.33
Unvested, Weighted-Average Grant Date Fair Value, Ending Balance \| $ / shares	$ 70.55

Equity-based Compensation - Restricted Stock - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 66,018,000	$ 49,524,000	$ 39,260,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of restricted stock vested	21,600,000	3,600,000	11,300,000
Stock Options [Member] \| Departing Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	600,000	100,000	3,800,000
Stock Options [Member] \| Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,900,000	$ 0	$ 0

Equity-based Compensation - Employee Stock Purchase Plan - Additional Information (Detail)	Oct. 19, 2016 shares
2016 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	400,000

Net Income (Loss) Per Share Attributable to Common Shareholders - Schedule of Computation of Basic and Diluted Net (Loss) Income per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Net (loss) income	$ (107,039)	$ (92,439)	$ (79,656)	$ (69,731)	$ 30,542	$ 138,423	$ (53,699)	$ (48,408)	$ (348,865)	$ 66,858	$ (164,981)
Basic weighted-average common shares outstanding	71,282,096	70,143,481	61,420,746	60,847,683	57,395,839	54,829,057	53,188,041	52,093,208	65,949,672	54,392,304	47,964,368
Effect of potentially dilutive securities:
Diluted weighted-average common shares outstanding	71,282,096	70,143,481	61,420,746	60,847,683	60,233,927	57,598,901	53,188,041	52,093,208	65,949,672	56,932,798	47,964,368
Basic net (loss) income per common share	$ (1.50)	$ (1.32)	$ (1.30)	$ (1.15)	$ 0.53	$ 2.52	$ (1.01)	$ (0.93)	$ (5.29)	$ 1.23	$ (3.44)
Diluted net (loss) income per common share	$ (1.50)	$ (1.32)	$ (1.30)	$ (1.15)	$ 0.51	$ 2.40	$ (1.01)	$ (0.93)	$ (5.29)	$ 1.17	$ (3.44)
Outstanding Options [Member]
Effect of potentially dilutive securities:
Effect of potentially dilutive securities										2,406,962
Unvested Restricted Common Shares [Member]
Effect of potentially dilutive securities:
Effect of potentially dilutive securities										133,532

Net Income (Loss) Per Share Attributable to Common Shareholders - Schedule of Antidilutive Securities not Include in Computation of Net (Loss) Income per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not include in computation of net income (loss) per share	9,007,329	3,897,754	7,016,653
Outstanding Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not include in computation of net income (loss) per share	8,101,980	3,789,129	6,689,311
Unvested Restricted Common Shares [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not include in computation of net income (loss) per share	894,092	108,625	327,342
ESPP [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not include in computation of net income (loss) per share	11,257

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Company contributions toward the plan	$ 1.9	$ 1.1	$ 0.6

Income Taxes - Schedule of (Loss) Income Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Domestic	$ 7,630	$ 9,155	$ 5,966
Foreign	(355,686)	58,151	(170,394)
Total	$ (348,056)	$ 67,306	$ (164,428)

Income Taxes - Schedule of (Provision for) Benefit from Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current income taxes:
Federal	$ (248)	$ (423)	$ (416)
State	(151)	(59)	(131)
Foreign	(1)	0	0
Total current income taxes	(400)	(482)	(547)
Deferred income taxes:
Federal	(409)	34	(6)
Total deferred income taxes	(409)	34	(6)
Total income tax (provision) benefit	$ (809)	$ (448)	$ (553)

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Income Taxes - Schedule of Reconciliation of Income Tax Expense Computed at Statutory Corporate Income Tax Rate to Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Effective Income Tax Rate
Income tax expense at statutory rate	11.90%	9.30%	9.30%
State income tax, net of federal benefit	1.00%	(2.10%)	0.70%
Nondeductible expenses	0.10%	(0.10%)	0.00%
Foreign rate differential	(0.10%)	2.00%	(0.40%)
Statutory to US GAAP permanent differences	0.00%	0.10%	1.00%
Stock-based compensation	2.30%	(2.00%)	1.40%
Impact of deferred rate change	0.00%	(12.20%)	0.00%
Research credits	3.30%	(5.20%)	1.80%
Change in valuation allowance	(18.70%)	10.90%	(14.10%)
Effective income tax rate	(0.20%)	0.70%	(0.30%)

Income Taxes - Schedule of Significant Components of Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 84,531	$ 31,496
Accruals and reserves	4,785	2,868
Operating lease liabilities	16,782	14,214
Other deferred tax assets	1,517	28
Stock-based compensation	9,605	5,217
Deferred revenue	86
Deferred revenue		(20)
Research credit	19,526	7,150
Total deferred tax assets	136,832	60,953
Less valuation allowance	(116,640)	(45,913)
Net deferred tax assets	20,192	15,040
Deferred tax liabilities:
Depreciation	(6,778)	(3,901)
Operating lease assets	(13,776)	(11,068)
Intangible assets	(31)	(40)
Other deferred tax liabilities	(4)	(20)
Total deferred tax liabilities	(20,589)	(15,029)
Long term deferred taxes, assets		$ 11
Long term deferred taxes, liabilities	$ (397)

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Valuation Allowance [Line Items]
Increase in valuation allowance	$ 70,700,000
Non-US Net operating loss carryforwards	$ 1,416,700,000
Operating loss carryforwards expiration period	2023
Unrecognized tax benefits, gross	$ 11,967,000	$ 5,231,000	$ 1,595,000	$ 354,000
Unrecognized tax benefits would favorably impact the effective tax rate if recognized	11,000,000.0
Accrued interest or penalties related to uncertain tax positions	0	0	0
Uncertain tax positions recognized	0	$ 0	$ 0
U.S. Domestic Federal [Member] \| Research and Development [Member]
Valuation Allowance [Line Items]
Tax credit carryforward amount	$ 13,900,000
Tax credit carryforward, expiration year	2040
Uncertain tax positions	$ 7,500,000
U.S. Domestic State [Member] \| Research and Development [Member]
Valuation Allowance [Line Items]
Tax credit carryforward amount	$ 6,900,000
Tax credit carryforward, expiration year	2034
Uncertain tax positions	$ 4,500,000
Switzerland [Member]
Valuation Allowance [Line Items]
Non-US Net operating loss carryforwards	707,600,000
Canton of Zug [Member]
Valuation Allowance [Line Items]
Non-US Net operating loss carryforwards	707,600,000
UNITED KINGDOM [Member]
Valuation Allowance [Line Items]
Non-US Net operating loss carryforwards	$ 1,500,000

Income Taxes - Schedule of Aggregate Changes in Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 5,231	$ 1,595	$ 354
Increases for tax positions taken during current period	7,004	2,754	1,212
Increases for tax positions taken in prior periods		882	29
Decreases for tax positions taken in prior periods	(268)
Balance at end of year	$ 11,967	$ 5,231	$ 1,595

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 370	$ 148	$ 44	$ 157	$ 77,016	$ 211,928	$ 318	$ 328	$ 719	$ 289,590	$ 3,124
Total operating expenses	108,131	92,547	80,733	73,743	66,033	72,765	55,301	48,751	355,154	242,850	162,067
Loss from operations	(107,761)	(92,399)	(80,689)	(73,586)	10,983	139,163	(54,983)	(48,423)	(354,435)	46,740	(158,943)
Net (loss) income	$ (107,039)	$ (92,439)	$ (79,656)	$ (69,731)	$ 30,542	$ 138,423	$ (53,699)	$ (48,408)	$ (348,865)	$ 66,858	$ (164,981)
Net (loss) income per common share:
Basic	$ (1.50)	$ (1.32)	$ (1.30)	$ (1.15)	$ 0.53	$ 2.52	$ (1.01)	$ (0.93)	$ (5.29)	$ 1.23	$ (3.44)
Diluted	$ (1.50)	$ (1.32)	$ (1.30)	$ (1.15)	$ 0.51	$ 2.40	$ (1.01)	$ (0.93)	$ (5.29)	$ 1.17	$ (3.44)
Weighted-average common shares outstanding:
Basic	71,282,096	70,143,481	61,420,746	60,847,683	57,395,839	54,829,057	53,188,041	52,093,208	65,949,672	54,392,304	47,964,368
Diluted	71,282,096	70,143,481	61,420,746	60,847,683	60,233,927	57,598,901	53,188,041	52,093,208	65,949,672	56,932,798	47,964,368

Related Party Transactions - Additional Information (Detail)	3 Months Ended
	Dec. 31, 2018
Collaboration Agreement [Member] \| Vertex Pharmaceuticals Inc [Member] \| Minimum [Member]
Related Party Transaction [Line Items]
Voting interest Percentage	10.00%