CRISPR Therapeutics (CRSP) 10-Q 27 Apr 21 2021 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 23, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
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 Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		75,768,936
Entity Current Reporting Status	Yes
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 Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 1,126,059	$ 1,168,620
Marketable securities	680,144	521,713
Accounts receivable	150	144
Prepaid expenses and other current assets	26,006	26,143
Total current assets	1,832,359	1,716,620
Property and equipment, net	51,913	42,160
Intangible assets, net	167	180
Restricted cash	16,844	16,848
Operating lease assets	50,129	50,865
Other non-current assets	6,498	1,293
Total assets	1,957,910	1,827,966
Current liabilities:
Accounts payable	13,072	9,094
Accrued expenses	49,864	53,782
Deferred revenue, current	1,802	2,341
Accrued tax liabilities	3,356	10,473
Operating lease liabilities	12,063	11,362
Other current liabilities	2,933	7,207
Total current liabilities	83,090	94,259
Deferred revenue, non-current	11,776	11,776
Operating lease liabilities, net of current portion	49,408	50,067
Other non-current liabilities	8,138	7,630
Total liabilities	152,412	163,732
Commitments and contingencies, see Note 6
Shareholders’ equity:
Common shares, CHF 0.03 par value, 115,172,786 shares authorized at March 31, 2021 and December 31, 2020, 75,925,944 and 74,110,160 shares issued at March 31, 2021 and December 31, 2020, respectively, 75,730,628 and 73,914,844 shares outstanding at March 31, 2021 and December 31, 2020, respectively.	2,340	2,277
Treasury shares, at cost, 195,316 shares at March 31, 2021 and December 31, 2020.	(63)	(63)
Additional paid-in capital	2,490,421	2,235,679
Accumulated deficit	(686,739)	(573,576)
Accumulated other comprehensive loss	(461)	(83)
Total shareholders' equity	1,805,498	1,664,234
Total liabilities and shareholders’ equity	$ 1,957,910	$ 1,827,966

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - SFr / shares	Mar. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Common stock, par value	SFr 0.03	SFr 0.03
Common stock, shares authorized	115,172,786	115,172,786
Common stock, shares issued	75,925,944	74,110,160
Common stock, shares outstanding	75,730,628	73,914,844
Treasury stock, shares	195,316	195,316

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue:
Total revenue	$ 539	$ 157
Operating expenses:
Research and development	90,565	54,193
General and administrative	24,517	19,550
Total operating expenses	115,082	73,743
Loss from operations	(114,543)	(73,586)
Other income (expense):
Other income, net	1,955	4,232
Total other income (expense), net	1,955	4,232
Net loss before income taxes	(112,588)	(69,354)
Provision for income taxes	(575)	(377)
Net loss	(113,163)	(69,731)
Foreign currency translation adjustment	5	(25)
Unrealized loss on marketable securities	(383)
Comprehensive loss	$ (113,541)	$ (69,756)
Net loss per common share — basic	$ (1.51)	$ (1.15)
Basic weighted-average common shares outstanding	75,005,187	60,847,683
Net loss per common share — diluted	$ (1.51)	$ (1.15)
Diluted weighted-average common shares outstanding	75,005,187	60,847,683
Collaboration Revenue [Member]
Revenue:
Total revenue	$ 202	$ 157
Grant Revenue [Member]
Revenue:
Total revenue	$ 337

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Shares [Member]	Treasury Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2019	$ 939,425	$ 1,847	$ (63)	$ 1,162,345	$ (224,711)	$ 7
Beginning balance (in shares) at Dec. 31, 2019		60,783,799	250,226
Vesting of restricted shares (in shares)		5,000
Exercise of vested options, value	1,388	$ 3		1,385
Exercise of vested options (in shares)		83,406
Stock-based compensation expense	14,151			14,151
Issuance of common shares related to license agreement	889			889
Issuance of common shares related to license agreement (in shares)		17,830	(17,830)
Other comprehensive loss	(25)					(25)
Net loss	(69,731)				(69,731)
Ending balance at Mar. 31, 2020	886,097	$ 1,850	$ (63)	1,178,770	(294,442)	(18)
Ending balance (in shares) at Mar. 31, 2020		60,890,035	232,396
Beginning balance at Dec. 31, 2019	939,425	$ 1,847	$ (63)	1,162,345	(224,711)	7
Beginning balance (in shares) at Dec. 31, 2019		60,783,799	250,226
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
Issuance of common shares, net of issuance costs	222,175	$ 45		222,130
Issuance of common shares, net of issuance costs (in shares)		1,353,121
Vesting of restricted shares	3	$ 3
Vesting of restricted shares (in shares)		109,355
Exercise of vested options, value	$ 9,784	$ 15		9,769
Exercise of vested options (in shares)	342,471	342,051
Purchase of common stock under ESPP	$ 751			751
Purchase of common stock under ESPP (in shares)		11,257
Stock-based compensation expense	22,092			22,092
Other comprehensive loss	(378)					(378)
Net loss	(113,163)				(113,163)
Ending balance at Mar. 31, 2021	$ 1,805,498	$ 2,340	$ (63)	$ 2,490,421	$ (686,739)	$ (461)
Ending balance (in shares) at Mar. 31, 2021		75,730,628	195,316

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Shareholders' Equity (Parenthetical) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)	Mar. 31, 2021SFr / shares	Mar. 31, 2020SFr / shares
Common shares, par value | SFr / shares		SFr 0.03
Stock Options [Member]
Issuance costs | $	$ 1.5
Common Shares [Member]
Issuance costs | $	$ 5.4
Common shares, par value | SFr / shares		SFr 0.03	SFr 0.03

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities:
Net loss	$ (113,163)	$ (69,731)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	2,715	2,091
Equity-based compensation	22,092	14,151
Other income, non-cash	2,064	890
Changes in:
Accounts receivable	(6)	(25,018)
Prepaid expenses and other assets	(5,068)	29,659
Accounts payable and accrued expenses	(5,770)	(2,496)
Deferred revenue	(539)	(157)
Operating lease assets and liabilities	778	37
Other liabilities, net	(3,766)	(1,601)
Net cash used in operating activities	(100,663)	(52,175)
Investing activities:
Purchase of property, plant and equipment	(7,024)	(2,991)
Purchases of marketable securities	(323,975)
Maturities of marketable securities	163,101
Net cash used in investing activities	(167,898)	(2,991)
Financing activities:
Proceeds from issuance of common shares, net of issuance costs	214,592
Proceeds from exercise of options and ESPP contributions, net of issuance costs	11,399	1,132
Net cash provided by financing activities	225,991	1,132
Effect of exchange rate changes on cash	5	(25)
Decrease in cash	(42,565)	(54,059)
Cash, cash equivalents and restricted cash, beginning of period	1,185,468	948,812
Cash, cash equivalents and restricted cash, end of period	1,142,903	894,753
Supplemental disclosure of non-cash investing and financing activities
Property and equipment purchases in accounts payable and accrued expenses	8,847	1,340
Equity issuance costs in accounts payable and accrued expenses	$ 2,868	$ 39

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Reconciliation to amounts within the condensed consolidated balance sheets
Cash and cash equivalents	$ 1,126,059	$ 1,168,620	$ 889,712
Restricted cash	16,844	16,848	5,041
Cash, cash equivalents and restricted cash at end of period	$ 1,142,903	$ 1,185,468	$ 894,753	$ 948,812

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	1. Basis of Presentation and Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements are unaudited and have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America, or GAAP. The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company views its operations and manages its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology. Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the financial position and results of operations for the three-month interim periods ended March 31, 2021 and 2020. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements for the year ended December 31, 2020, which are contained in the 2020 Annual Report on Form 10-K filed with the Securities and Exchange Commission, or the SEC, on February 16, 2021. Use of Estimates 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 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. Changes in estimates are reflected in reported results in the period in which they become known. Significant Accounting Policies The significant accounting policies used in preparation of these condensed consolidated financial statements for the three months ended March 31, 2021 are consistent with those discussed in Note 2 to the consolidated financial statements in the Company’s 2020 Annual Report on Form 10-K filed with the SEC on February 16, 2021. 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. 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.

Marketable Securities

Marketable Securities	3 Months Ended
	Mar. 31, 2021
Investments Debt And Equity Securities [Abstract]
Marketable Securities	2. Marketable Securities The following table summarizes cash equivalents and marketable securities held at March 31, 2021 and December 31, 2020 (in thousands), which are recorded at fair value. The table below excludes $494.2 million and $395.1 million of cash at March 31, 2021 and December 31, 2020, respectively. Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value March 31, 2021 Cash equivalents: Money market funds $ 629,357 $ — $ — $ 629,357 Corporate debt securities 2,533 1 (2 ) 2,532 Certificates of deposit — — — — Commercial paper — — — — Total cash equivalents 631,890 1 (2 ) 631,889 Marketable securities: U.S. Treasury securities — — — — Corporate debt securities 536,144 37 (551 ) 535,630 Certificates of deposit 54,273 — — 54,273 Government-sponsored enterprise securities 3,120 — (1 ) 3,119 Commercial paper 87,120 2 — 87,122 Total marketable securities 680,657 39 (552 ) 680,144 Total cash equivalents and marketable securities $ 1,312,547 $ 40 $ (554 ) $ 1,312,033 December 31, 2020 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 As of March 31, 2021 and December 31, 2020, the aggregate fair value of marketable securities that were in an unrealized loss position for less than twelve months was $473.7 million and $280.3 million, respectively. As of March 31, 2021 and 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 $0.4 million during the three months ended March 31, 2021 related to its debt securities, which is included in comprehensive loss on the condensed consolidated statements of operations and comprehensive loss. No unrealized losses related to debt securities were recorded during the three months ended March 31, 2020. The Company determined that there is no material credit risk associated with the above investments as of March 31, 2021. As such, an allowance for credit losses was not recognized. As of March 31, 2021, 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 basis. No available-for-sale debt securities held as of March 31, 2021 had remaining maturities greater than two years.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements 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 March 31, 2021 and December 31, 2020 (in thousands): Fair Value Measurements at March 31, 2021 Total Level 1 Level 2 Level 3 Cash and cash equivalents: Cash $ 494,170 $ 494,170 $ — $ — Money market funds 629,357 629,357 — — Corporate debt securities 2,532 — 2,532 — Certificates of deposit — — — — Commercial paper — — — — Marketable securities: U.S. Treasury securities — — — — Corporate debt securities 535,630 — 535,630 — Certificates of deposit 54,273 — 54,273 — Government-sponsored enterprise securities 3,119 — 3,119 — Commercial paper 87,122 — 87,122 — Other non-current assets 2,212 — — 2,212 Total $ 1,808,415 $ 1,123,527 $ 682,676 $ 2,212 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 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.

Property and Equipment, net

Property and Equipment, net	3 Months Ended
	Mar. 31, 2021
Property Plant And Equipment [Abstract]
Property and Equipment, net	4. Property and Equipment, net Property and equipment, net, consists of the following (in thousands): As of March 31, December 31, 2021 2020 Computer equipment $ 1,472 $ 727 Furniture, fixtures and other 3,420 3,416 Laboratory equipment 27,956 25,353 Leasehold improvements 25,977 25,473 Construction work in process 16,969 8,366 Total property and equipment, gross 75,794 63,335 Accumulated depreciation (23,881 ) (21,175 ) Total property and equipment, net $ 51,913 $ 42,160 Depreciation expense for the three months ended March 31, 2021 and 2020 was $2.7 million and $2.1 million, respectively.

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2021
Payables And Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses consist of the following (in thousands): As of March 31, December 31, 2021 2020 Payroll and employee-related costs $ 11,565 $ 22,402 Research costs 22,034 21,684 Licensing fees 930 1,401 Professional fees 1,874 1,670 Intellectual property costs 5,229 3,625 Accrued property and equipment 6,869 2,835 Other 1,363 165 Total $ 49,864 $ 53,782

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Future Lease Commitments The Company has entered into certain leasing commitments for which right of use assets and right of use liabilities are not reflected on the consolidated balance sheet as the leases have not yet commenced. In November 2019, the Company, together with one of its partners, committed to making $3.9 million in annual rental payments to a clinical manufacturing organization under a lease arrangement for a five-year In July 2020, the Company entered into a lease agreement for an office and laboratory facility in Boston, Massachusetts, or the 2020 Boston Lease. In accordance with ASC 842, Leases 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. Letters of Credit As of March 31, 2021, the Company had restricted cash of $16.8 million, representing letters of credit securing the Company’s obligations under certain leased facilities. The letters of credit are secured by cash held in a restricted depository account. The cash deposit is recorded in restricted cash in the accompanying condensed consolidated balance sheet as of March 31, 2021. Research, Manufacturing, License and Intellectual Property Agreements The Company has engaged several research institutions and companies to identify new delivery strategies and applications of the Company’s gene-editing technology. The Company is also a party to a number of license agreements which require significant upfront payments and may be required to make 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 Pharmaceuticals Incorporated and certain of its subsidiaries, or Vertex, is eligible to receive up to $395.0 million in potential specified research, development, regulatory and commercial milestones and tiered single-digit percentage royalties on future net sales. Refer to Note 7 for further discussion on the Company’s arrangements with Vertex.

Significant Contracts

Significant Contracts	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Significant Contracts	7. 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 reacquired the exclusive rights and agreed to 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, Revenue from Contracts with Customers Collaborative Agreements Research and Development 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 March 31, 2021. 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 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 three months ended March 31, 2021 and 2020, respectively, was not material. As of March 31, 2021 and December 31, 2020, there was $0.2 million and $0.4 million of current deferred revenue related to the collaboration with Vertex. As of March 31, 2021, there was $11.8 million of non-current deferred revenue related to the collaboration with Vertex, which is unchanged from December 31, 2020. The transaction price allocated to the remaining performance obligations was $11.8 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 March 31, 2021. 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 three months ended March 31, 2021 and 2020, the Company recognized $19.9 million and $9.1 million of research and development expense related to the Vertex Agreements, respectively. Research and development expense for the three months ended March 31, 2021 and 2020 was net of $10.6 million and $5.5 million of reimbursements from Vertex, respectively. Accounting Analysis under ASC 730 In connection with the 2019 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 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 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 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 Transactions under the 2015 Casebia Agreements ceased on the effective date of the 2019 Casebia Agreements. There was no financial impact of the 2015 Casebia Agreements for the three months ended March 31, 2021 and 2020. 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 variable interest entity, for which it became the primary beneficiary. As such, under ASC 810, Consolidation Business Combinations 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 During the three months ended March 31, 2021 and 2020, the Company recorded a benefit of $4.3 million and $1.9 million, respectively, to research and development expense for qualifying expenses incurred under the 2019 Option Agreement. As of March 31, 2021 and December 31, 2020, t he Company has recorded $ million and $7.0 million, respectively, in other current liabilities relating to certain research and development obligations to be satisfied within one year of the balance sheet date. As of March 31, 2021, the Company has recorded $ million in other long-term liabilities consisting of the previously allocated 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, which is unchanged from December 31, 2020

Share Capital

Share Capital	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Share Capital	8. Share Capital The Company had 115,172,786 authorized common shares as of March 31, 2021, with a par value of CHF 0.03 per share. Share Capital consisted of the following: As of Type of Share Capital Conditional Capital March 31, 2021 December 31, 2020 Common shares Registered share capital 80,321,227 75,133,951 Common shares Authorized share capital 14,125,426 17,625,426 Common shares Conditional share capital - Bonds or similar debt instruments 4,919,700 4,919,700 Common shares Conditional share capital - Employee benefit plans 15,806,433 17,493,709 Total 115,172,786 115,172,786 At-the-Market Offerings In August 2019, the Company entered into an Open Market Sale Agreement SM 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 ATM 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 on this amount was payable as of March 31, 2021. 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, or the 2021 ATM. As of March 31, 2021, 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 on this amount was payable as of March 31, 2021. July 2020 Offering 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 $484.8 million, which were net of equity issuance costs and stamp tax of $32.5 million.

Stock-based Compensation

Stock-based Compensation	3 Months Ended
	Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	9. Stock-based Compensation During the three months ended March 31, 2021, the Company recognized the following stock-based compensation expense (in thousands): Three Months Ended March 31, 2021 2020 Research and development $ 12,845 $ 7,362 General and administrative 9,247 6,789 Total $ 22,092 $ 14,151 Stock option activity The following table summarizes stock option activity for the three months ended March 31, 2021: Shares Weighted- average exercise price per share Outstanding at December 31, 2020 8,101,980 $ 42.44 Granted 882,558 139.05 Exercised (342,471 ) 33.12 Cancelled or forfeited (69,404 ) 43.31 Outstanding at March 31, 2021 8,572,663 $ 52.76 Exercisable at March 31, 2021 3,962,897 $ 31.48 Vested and expected to vest at March 31, 2021 8,572,663 $ 52.76 As of March 31, 2021, total unrecognized compensation expense related to stock options was $191.3 million, which the Company expects to recognize over a remaining weighted-average period of 3.1 years. Restricted stock activity The following table summarizes restricted stock activity for the three months ended March 31, 2021: Restricted Stock Weighted- Average Grant Date Fair Value Unvested balance as of December 31, 2020 894,092 $ 70.55 Granted 278,645 136.16 Vested (109,355 ) 40.64 Cancelled or forfeited (11,003 ) 57.94 Unvested balance as of March 31, 2021 1,052,379 $ 91.16 As of March 31, 2021, total unrecognized compensation expense related to unvested restricted common shares was $76.5 million, which the Company expects to recognize over a remaining weighted-average vesting period of 2.8 years.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Shareholders	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Shareholders	10. Basic net loss per share is calculated by dividing net loss attributable to common shareholders by the weighted-average number of common shares outstanding during the period. Diluted net loss per share is calculated by dividing the net loss 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 is net loss attributable to common shareholders for all periods presented. The following common stock equivalents were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect (in thousands): Three Months Ended March 31, 2021 2020 Outstanding options 8,572,663 8,495,315 Unvested restricted common shares 1,052,379 967,060 ESPP 10,594 — Total 9,635,636 9,462,375

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes During the three months ended March 31, 2021 and 2020, the Company recorded an income tax provision of $0.6 million and $0.4 million, respectively, representing an effective tax rate of -0.5% and -0.5%, respectively. The income tax provision is primarily attributable to the year-to-date pre-tax income earned by the Company’s U.S. subsidiary. The difference in the statutory tax rate and effective tax rate is primarily a result of the jurisdictional mix of earnings and losses that are not benefited. The Company maintains a valuation allowance against certain deferred tax assets that are not more-likely-than-not realizable. As a result, the Company has not recognized a tax benefit related to losses generated in Switzerland in the current periods. 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.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events As described in Note 7, in December 2017, the Company and Vertex entered into the JDA pursuant to which the parties agreed to, among other things, co-develop and co-commercialize CTX001 and other product candidates specified in the JDA. On April 16, 2021, the Company and Vertex agreed to amend and restate the JDA and entered into an Amended and Restated Joint Development and Commercialization Agreement (the “A&R JDCA”), pursuant to which the parties agreed to, among other things, (a) adjust the governance structure for the collaboration and adjust the responsibilities of each party thereunder; (b) adjust the allocation of net profits and net losses between the parties with respect to CTX001 only; and (c) exclusively license (subject to the Company’s reserved rights to conduct certain activities) certain intellectual property rights to Vertex relating to the specified product candidates and products (including CTX001) that may be researched, developed, manufactured and commercialized under such agreement. The A&R JDCA includes, among other things, provisions relating to the following: Governance; Activities . The Company and Vertex will establish the following committees: (i) a joint oversight committee to provide high-level oversight and (ii) a transition committee to provide for forum planning, discussing and sharing information regarding certain transition activities until completion of such activities. Effective as of the closing of the transaction contemplated by the A&R JDCA, the previously established collaboration strategy team and all working groups established by such team will be disbanded. Each of the committees will contain an equal number of representatives from each of the Company and Vertex. The A&R JDCA provides that, subject to the terms and conditions of such agreement, Vertex will have the right to conduct all research, development, manufacturing and commercialization activities relating to the specified product candidates and products (including CTX001) throughout the world subject to the Company’s reserved right to conduct certain activities. The Company continues to participate in certain aspects of such activities in an observer capacity unless and to the extent otherwise agreed to by the parties. Financial Terms . In connection with the closing of the transaction contemplated by the A&R JDCA, the Company will receive a $900 million up-front payment from Vertex and a one-time $200 million milestone payment upon receipt by Vertex of the first marketing approval of the initial product candidate from the U.S. Food and Drug Administration or the European Commission. The net profits and net losses, as applicable, incurred under the A&R JDCA with respect to all product candidates and products specified in the A&R JDCA other than CTX001 shall be shared equally between the Company and Vertex. With respect to CTX001 only, the net profits and net losses, as applicable, incurred under the A&R JDCA through July 1, 2021 (or such applicable later date in the event HSR clearance has not been received by October 1, 2021) in connection with the initial shared product (i.e., CTX001) will be shared equally between the Company and Vertex, and beginning July 1, 2021 (or such applicable later date in the event HSR clearance has not been received by October 1, 2021), the net profits and net losses, as applicable, incurred under the A&R JDCA will be allocated 40% to the Company and 60% to Vertex. Termination . Either party can terminate the A&R JDCA upon the other party’s material breach, subject to specified notice and cure provisions, or, in the case of Vertex, in the event that the Company becomes subject to specified bankruptcy, winding up or similar circumstances. Either party may terminate the A&R JDCA in the event the other party commences or participates in any action or proceeding challenging the validity or enforceability of any patent that is licensed to such challenging party pursuant to the A&R JDCA. Vertex also has the right to terminate the A&R JDCA for convenience at any time after giving prior written notice. If circumstances arise pursuant to which a party would have the right to terminate the A&R JDCA on account of an uncured material breach, such party may elect to keep the A&R JDCA in effect and cause such breaching party to be treated as if it had exercised its opt-out rights with respect to the products associated with such uncured material breach (described below) and the royalties payable to the breaching party would be reduced by a specified percentage. Opt-Out Rights . Either party may opt out of the development of a product candidate under the A&R JDCA after predetermined points in the development of the product candidate, on a candidate-by-candidate basis. In the event of such opt-out, the party opting-out will no longer share in the net profits and net losses associated with such product candidate and, instead, the opting-out party will be entitled to high single to mid-teen percentage royalties on the net sales of such product, if commercialized. The closing of the transaction contemplated by the A&R JDCA is subject to certain conditions including the expiration of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act and any other required antitrust clearance.

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements are unaudited and have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America, or GAAP. The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company views its operations and manages its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology. Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the financial position and results of operations for the three-month interim periods ended March 31, 2021 and 2020. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements for the year ended December 31, 2020, which are contained in the 2020 Annual Report on Form 10-K filed with the Securities and Exchange Commission, or the SEC, on February 16, 2021.
Use of Estimates	Use of Estimates 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 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. Changes in estimates are reflected in reported results in the period in which they become known.
New Accounting Pronouncements - Recently Adopted	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. 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.

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2021
Investments Debt And Equity Securities [Abstract]
Summary of Cash Equivalents and Marketable Securities Recorded at Fair Value	The following table summarizes cash equivalents and marketable securities held at March 31, 2021 and December 31, 2020 (in thousands), which are recorded at fair value. The table below excludes $494.2 million and $395.1 million of cash at March 31, 2021 and December 31, 2020, respectively. Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value March 31, 2021 Cash equivalents: Money market funds $ 629,357 $ — $ — $ 629,357 Corporate debt securities 2,533 1 (2 ) 2,532 Certificates of deposit — — — — Commercial paper — — — — Total cash equivalents 631,890 1 (2 ) 631,889 Marketable securities: U.S. Treasury securities — — — — Corporate debt securities 536,144 37 (551 ) 535,630 Certificates of deposit 54,273 — — 54,273 Government-sponsored enterprise securities 3,120 — (1 ) 3,119 Commercial paper 87,120 2 — 87,122 Total marketable securities 680,657 39 (552 ) 680,144 Total cash equivalents and marketable securities $ 1,312,547 $ 40 $ (554 ) $ 1,312,033 December 31, 2020 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 Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Financial Assets Measured at Fair Value on Recurring Basis	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 March 31, 2021 and December 31, 2020 (in thousands): Fair Value Measurements at March 31, 2021 Total Level 1 Level 2 Level 3 Cash and cash equivalents: Cash $ 494,170 $ 494,170 $ — $ — Money market funds 629,357 629,357 — — Corporate debt securities 2,532 — 2,532 — Certificates of deposit — — — — Commercial paper — — — — Marketable securities: U.S. Treasury securities — — — — Corporate debt securities 535,630 — 535,630 — Certificates of deposit 54,273 — 54,273 — Government-sponsored enterprise securities 3,119 — 3,119 — Commercial paper 87,122 — 87,122 — Other non-current assets 2,212 — — 2,212 Total $ 1,808,415 $ 1,123,527 $ 682,676 $ 2,212 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

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	3 Months Ended
	Mar. 31, 2021
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net, consists of the following (in thousands): As of March 31, December 31, 2021 2020 Computer equipment $ 1,472 $ 727 Furniture, fixtures and other 3,420 3,416 Laboratory equipment 27,956 25,353 Leasehold improvements 25,977 25,473 Construction work in process 16,969 8,366 Total property and equipment, gross 75,794 63,335 Accumulated depreciation (23,881 ) (21,175 ) Total property and equipment, net $ 51,913 $ 42,160

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2021
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): As of March 31, December 31, 2021 2020 Payroll and employee-related costs $ 11,565 $ 22,402 Research costs 22,034 21,684 Licensing fees 930 1,401 Professional fees 1,874 1,670 Intellectual property costs 5,229 3,625 Accrued property and equipment 6,869 2,835 Other 1,363 165 Total $ 49,864 $ 53,782

Significant Contracts (Tables)

Significant Contracts (Tables)	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Fair Value of Assets and Liabilities Received	As a result of the Retirement Agreement, the Company determined that it had obtained a controlling interest in a variable interest entity, for which it became the primary beneficiary. As such, under ASC 810, Consolidation Business Combinations 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)

Share Capital (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Schedule of Share Capital	Share Capital consisted of the following: As of Type of Share Capital Conditional Capital March 31, 2021 December 31, 2020 Common shares Registered share capital 80,321,227 75,133,951 Common shares Authorized share capital 14,125,426 17,625,426 Common shares Conditional share capital - Bonds or similar debt instruments 4,919,700 4,919,700 Common shares Conditional share capital - Employee benefit plans 15,806,433 17,493,709 Total 115,172,786 115,172,786

Stock-based Compensation (Table

Stock-based Compensation (Tables)	3 Months Ended
	Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock-Based Compensation Expense	During the three months ended March 31, 2021, the Company recognized the following stock-based compensation expense (in thousands): Three Months Ended March 31, 2021 2020 Research and development $ 12,845 $ 7,362 General and administrative 9,247 6,789 Total $ 22,092 $ 14,151
Summary of Stock Option Activity	The following table summarizes stock option activity for the three months ended March 31, 2021: Shares Weighted- average exercise price per share Outstanding at December 31, 2020 8,101,980 $ 42.44 Granted 882,558 139.05 Exercised (342,471 ) 33.12 Cancelled or forfeited (69,404 ) 43.31 Outstanding at March 31, 2021 8,572,663 $ 52.76 Exercisable at March 31, 2021 3,962,897 $ 31.48 Vested and expected to vest at March 31, 2021 8,572,663 $ 52.76
Summary of Restricted Stock Activity	The following table summarizes restricted stock activity for the three months ended March 31, 2021: Restricted Stock Weighted- Average Grant Date Fair Value Unvested balance as of December 31, 2020 894,092 $ 70.55 Granted 278,645 136.16 Vested (109,355 ) 40.64 Cancelled or forfeited (11,003 ) 57.94 Unvested balance as of March 31, 2021 1,052,379 $ 91.16

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Shareholders (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities not Include in Computation of Net Loss per Share	The following common stock equivalents were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect (in thousands): Three Months Ended March 31, 2021 2020 Outstanding options 8,572,663 8,495,315 Unvested restricted common shares 1,052,379 967,060 ESPP 10,594 — Total 9,635,636 9,462,375

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021Segment
Accounting Policies [Abstract]
Number of operating segments	1

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Marketable securities	$ 494,200,000		$ 395,100,000
Marketable securities unrealized loss, Less than twelve months	473,700,000		280,300,000
Marketable securities unrealized loss, more than twelve months	0		$ 0
Unrealized loss, net	400,000	$ 0
Available-for-sale debt securities remaining maturities greater than two years	$ 0

Marketable Securities - Summary

Marketable Securities - Summary of Cash Equivalents and Marketable Securities Recorded at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Cash equivalents, amortized cost	$ 631,890	$ 773,560
Cash equivalents, gross unrealized gains	1	1
Cash equivalents, gross unrealized losses	(2)	(24)
Cash equivalents, fair value	631,889	773,537
Marketable securities, amortized cost	680,657	521,820
Marketable securities, gross unrealized gains	39	51
Marketable securities, gross unrealized losses	(552)	(158)
Marketable securities, fair value	680,144	521,713
Cash equivalents and marketable securities, amortized cost	1,312,547	1,295,380
Cash equivalents and marketable securities, gross unrealized gains	40	52
Cash equivalents and marketable securities, gross unrealized losses	(554)	(182)
Cash equivalents and marketable securities, fair value	1,312,033	1,295,250
Money Market Funds [Member]
Marketable Securities [Line Items]
Cash equivalents, amortized cost	629,357	742,958
Cash equivalents, fair value	629,357	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	54,273	25,162
Marketable securities, fair value	54,273	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	87,120	90,375
Marketable securities, gross unrealized gains	2
Marketable securities, fair value	87,122	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	2,533	2,526
Cash equivalents, gross unrealized gains	1	1
Cash equivalents, gross unrealized losses	(2)	(24)
Cash equivalents, fair value	2,532	2,503
Marketable securities, amortized cost	536,144	324,569
Marketable securities, gross unrealized gains	37	43
Marketable securities, gross unrealized losses	(551)	(156)
Marketable securities, fair value	535,630	324,456
Government-sponsored Enterprise Securities [Member]
Marketable Securities [Line Items]
Marketable securities, amortized cost	3,120	33,738
Marketable securities, gross unrealized gains		5
Marketable securities, gross unrealized losses	(1)	(2)
Marketable securities, fair value	$ 3,119	$ 33,741

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 6,784
Marketable securities, fair value	680,144	$ 521,713
Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other non-current assets	2,212	600
Total	1,808,415	1,690,933
Recurring Basis [Member] | Cash [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	494,170	395,083
Recurring Basis [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	629,357	742,958
Recurring Basis [Member] | Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	2,532	2,503
Marketable securities, fair value	535,630	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	54,273	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	87,122	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	3,119	33,741
Recurring Basis [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	1,123,527	1,138,041
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	494,170	395,083
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	629,357	742,958
Recurring Basis [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	682,676	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	2,532	2,503
Marketable securities, fair value	535,630	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	54,273	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	87,122	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	3,119	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	2,212	600
Total	$ 2,212	$ 600

Property and Equipment, net - S

Property and Equipment, net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 75,794	$ 63,335
Accumulated depreciation	(23,881)	(21,175)
Total property and equipment, net	51,913	42,160
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	1,472	727
Furniture, Fixtures and Other [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	3,420	3,416
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	27,956	25,353
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	25,977	25,473
Construction Work in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 16,969	$ 8,366

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Property Plant And Equipment [Abstract]
Depreciation expense	$ 2.7	$ 2.1

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accrued Liabilities Current [Abstract]
Payroll and employee-related costs	$ 11,565	$ 22,402
Research costs	22,034	21,684
Licensing fees	930	1,401
Professional fees	1,874	1,670
Intellectual property costs	5,229	3,625
Accrued property and equipment	6,869	2,835
Other	1,363	165
Total	$ 49,864	$ 53,782

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended
	Jul. 31, 2020	Nov. 30, 2019	Mar. 31, 2021
Contingencies And Commitments [Line Items]
Rental payments period	152 months	5 years
Letter of Credit [Member]
Contingencies And Commitments [Line Items]
Letters of credit secured by cash held in restricted depository account			$ 16.8
Lease Arrangement [Member]
Contingencies And Commitments [Line Items]
Annual rental payments		$ 3.9
Lease Arrangement [Member] | Minimum [Member]
Contingencies And Commitments [Line Items]
Rental payments	$ 292.5
2015 Collaboration Agreement [Member] | Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member]
Contingencies And Commitments [Line Items]
Milestone payment receivable			$ 395

Significant Contracts - Additio

Significant Contracts - Additional Information (Detail)	Dec. 13, 2019USD ($)Product	Oct. 26, 2015USD ($)	Oct. 31, 2019License	Mar. 31, 2021USD ($)Option	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2020USD ($)	Apr. 30, 2020USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Non-current deferred revenue				$ 11,776,000			$ 11,776,000
Collaboration revenue				539,000	$ 157,000
Current deferred revenue				1,802,000			2,341,000
Research and development expense				$ 90,565,000	54,193,000
Date of joint venture agreement				Dec. 19, 2015
Operating expenses				$ 115,082,000	73,743,000
Casebia Therapeutics Limited Liability Partnership [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Date of formation of joint venture entity				Feb. 12, 2016
Equity method investment, ownership percentage				50.00%
Business combination, consideration transferred				$ 41,000,000
Net assets acquired				16,000,000
Fair value of controlling interest obtained				32,000,000
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
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
Operating expenses	$ 6,000,000
2019 Option Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense				$ 4,300,000	1,900,000
2019 Option Agreement [Member] | Casebia Therapeutics Limited Liability Partnership [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of options exercised under agreement | Option				2
Equity method investment, ownership percentage				50.00%
Number of products | Product	2
Non-refundable one-time option payment	$ 20,000,000
Business combination, consideration transferred				$ 25,000,000
Payment to acquire business				16,000,000
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 | Casebia Therapeutics Limited Liability Partnership [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Fair value of obligations				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%
2019 Casebia Agreement [Member] | Other Current Liabilities [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research obligation				2,700,000			7,000,000
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
2019 Casebia Agreement [Member] | Casebia Therapeutics Limited Liability Partnership [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Fair value of assets and liabilities				16,000,000
Equity method investment				0
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		175,000,000
Transaction price				268,600,000
Non-current deferred revenue				11,800,000			11,800,000
Non-cash consideration received				10,000,000
Transaction price allocated to remaining performance obligations				11,800,000
Collaboration revenue				0	0
Current deferred revenue				200,000			$ 400,000
Maximum potential future payments				800,000,000
Research and development expense				19,900,000	9,100,000
Reimbursements from research and license agreements				10,600,000	$ 5,500,000
Collaborative arrangement, license rights reacquired by waiving payment owed				10,000,000
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
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
Milestone payment receivable				410,000,000
Transaction price allocated to remaining performance obligations				46,700,000
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
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
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
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
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] | Joint Development Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Up-front payment received		7,000,000		$ 7,000,000
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
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
Maximum potential payments				$ 825,000,000
Percentage of exchange payment of research and development costs				50.00%
Non-cash consideration expensed upon execution of collaborative agreement				$ 10,000,000
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
Percentage of exchange payment of research and development costs				50.00%
Number of options would not be exercised under agreement | Option				1
Number of remaining options under agreement | Option				4
Non-current deferred revenue				$ 57,800,000
Number of options exercised under agreement | Option				4
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
Transaction price allocated to remaining performance obligations				$ 6,700,000
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
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
Number of exclusive license targets | License			3
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

Significant Contracts - Schedul

Significant Contracts - Schedule of Fair Value of Assets and Liabilities Received (Detail) $ in Thousands	Mar. 31, 2021USD ($)
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 Info

Share Capital - Additional Information (Detail)	1 Months Ended				3 Months Ended	12 Months Ended
	Jan. 31, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)shares	Jul. 31, 2020USD ($)$ / sharesshares	Aug. 31, 2019USD ($)	Mar. 31, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares	Mar. 31, 2021SFr / shares	Dec. 31, 2020SFr / shares	Aug. 31, 2019SFr / shares
Class of Stock [Line Items]
Common stock, shares authorized | shares		115,172,786			115,172,786	115,172,786
Common shares, par value | SFr / shares							SFr 0.03	SFr 0.03
Proceeds from issuance of common shares					$ 214,592,000
July 2020 Offering [Member]
Class of Stock [Line Items]
Common shares sold | shares			7,400,000
Proceeds from issuance of common shares			$ 484,800,000
Common shares price per share | $ / shares			$ 70
Equity issuance costs			$ 32,500,000
Sales Agreement With Jefferies LLC [Member] | 2019 ATM [Member]
Class of Stock [Line Items]
Common shares, par value | SFr / shares									SFr 0.03
Common shares sold | shares						2,200,000
Average issue price of common shares | $ / shares						$ 89.47
Proceeds from issuance of common shares						$ 195,500,000
Equity issuance costs						$ 4,500,000
Sales Agreement With Jefferies LLC [Member] | 2020 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds	$ 46,700,000
Common shares sold | shares	300,000					1,800,000
Average issue price of common shares | $ / shares	$ 162.46					$ 169.57
Proceeds from issuance of common shares						$ 298,000,000
Equity issuance costs	$ 700,000					4,500,000
Payments of stamp taxes related to securities					500,000	4,900,000
Payable of stamp taxes related to securities		$ 4,000,000				$ 4,000,000
Sales Agreement With Jefferies LLC [Member] | 2021 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds					$ 177,800,000
Common shares sold | shares					1,100,000
Average issue price of common shares | $ / shares					$ 169.82
Equity issuance costs					$ 2,400,000
Payable of stamp taxes related to securities					$ 1,800,000
Sales Agreement With Jefferies LLC [Member] | Maximum [Member] | 2019 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds				$ 200,000,000
Sales Agreement With Jefferies LLC [Member] | Maximum [Member] | 2020 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds		$ 350,000,000
Sales Agreement With Jefferies LLC [Member] | Maximum [Member] | 2021 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds	$ 600,000,000

Share Capital - Schedule of Sha

Share Capital - Schedule of Share Capital (Detail) - shares	Mar. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Registered share capital	80,321,227	75,133,951
Authorized share capital	115,172,786	115,172,786
Employee Benefit Plans [Member]
Class of Stock [Line Items]
Conditional share capital - Bonds or similar debt instruments	15,806,433	17,493,709
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	14,125,426	17,625,426

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 22,092	$ 14,151
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	12,845	7,362
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 9,247	$ 6,789

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Stock Option Activity (Detail)	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]
Shares, Outstanding, Beginning Balance | shares	8,101,980
Shares, Granted | shares	882,558
Shares, Exercised | shares	(342,471)
Shares, Cancelled or forfeited | shares	(69,404)
Shares, Outstanding, Ending Balance | shares	8,572,663
Shares, Exercisable | shares	3,962,897
Shares, Vested or expected to vest | shares	8,572,663
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 42.44
Weighted-Average Exercise Price, Granted | $ / shares	139.05
Weighted-Average Exercise Price, Exercised | $ / shares	33.12
Weighted-Average Exercise Price, Cancelled or forfeited | $ / shares	43.31
Weighted-Average Exercise Price, Outstanding, Ending Balance | $ / shares	52.76
Weighted-Average Exercise Price, Exercisable | $ / shares	31.48
Weighted-Average Exercise Price, Vested or expected to vest | $ / shares	$ 52.76

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock options	$ 191.3
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, remaining weighted-average period for recognition	3 years 1 month 6 days
Restricted Common Shares [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
Total unrecognized compensation expense	$ 76.5

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Restricted Stock Activity (Detail) - Restricted Stock [Member]	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted common shares, Number of Shares, Beginning Balance | shares	894,092
Unvested restricted common shares, Number of Shares, Granted | shares	278,645
Unvested restricted common shares, Number of Shares, Vested | shares	(109,355)
Unvested restricted common shares, Number of Shares, Cancelled or forfeited | shares	(11,003)
Unvested restricted common shares, Number of Shares, Ending Balance | shares	1,052,379
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Beginning Balance | $ / shares	$ 70.55
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Granted | $ / shares	136.16
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Vested | $ / shares	40.64
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Cancelled or forfeited | $ / shares	57.94
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Ending Balance | $ / shares	$ 91.16

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Shareholders - Schedule of Antidilutive Securities not Include in Computation of Net Loss per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not include in computation of net loss per share	9,635,636	9,462,375
Outstanding Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not include in computation of net loss per share	8,572,663	8,495,315
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 loss per share	1,052,379	967,060
ESPP [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not include in computation of net loss per share	10,594

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income tax provision	$ 575	$ 377
Effective income tax rate	(0.50%)	(0.50%)

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - A&R JDCA [Member] - USD ($) $ in Millions	Jul. 01, 2021	Apr. 16, 2021
Forecast [Member]
Subsequent Event [Line Items]
Percentage of net profits and net losses	40.00%
Forecast [Member] | Vertex Pharmaceuticals Inc [Member]
Subsequent Event [Line Items]
Percentage of net profits and net losses	60.00%
Subsequent Event [Member] | Vertex Pharmaceuticals Inc [Member]
Subsequent Event [Line Items]
Up-front payment receivable		$ 900
Milestone payment receivable upon receipt of first marketing approval		$ 200