CRISPR Therapeutics (CRSP) 10-K 12 Feb 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Feb. 07, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Title of 12(b) Security	Common Shares, nominal value CHF 0.03 par value
Trading Symbol	CRSP
Security Exchange Name	NASDAQ
Entity Registrant Name	CRISPR THERAPEUTICS AG
Entity Central Index Key	0001674416
Entity Tax Identification Number	00-0000000
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity File Number	001-37923
Entity Address, Address Line One	Baarerstrasse 14
Entity Address, City or Town	Zug
Entity Address, Country	CH
Entity Address, Postal Zip Code	6300
City Area Code	41 (0)41
Local Phone Number	561 32 77
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	V8
Document Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		60,845,708
Entity Public Float			$ 2.5
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to the 2020 Annual General Meeting of Shareholders, which the Registrant intends to file with the Securities and Exchange Commission pursuant to Regulation 14A within 120 days after the end of the Registrant’s fiscal year ended December 31, 2019, are incorporated by reference into Part III of this Report.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 943,771	$ 456,649
Accounts receivable, including related party amounts of $0 and $88 as of December 31, 2019 and 2018, respectively	99	88
Prepaid expenses and other current assets, including related party amounts of $0 and $3,417 as of December 31, 2019 and 2018, respectively	43,677	9,658
Total current assets	987,547	466,395
Property and equipment, net	31,330	18,500
Intangible assets, net	235	289
Restricted cash	5,041	3,163
Operating lease assets	41,502
Other non-current assets	1,097	669
Total assets	1,066,752	489,016
Current liabilities:
Accounts payable	5,944	5,069
Accrued expenses, including related party amounts of $0 and $1,700 as of December 31, 2019 and 2018, respectively	30,180	20,852
Deferred revenue current, including related party amounts of $0 and $102 as of December 31, 2019 and 2018, respectively	960	102
Accrued tax liabilities	583	402
Deferred rent		1,202
Operating lease liabilities	8,489
Other current liabilities	10,950	119
Total current liabilities	57,106	27,746
Deferred revenue, including related party amounts of $0 and $57,780 as of December 31, 2019 and 2018, respectively	11,776	57,780
Deferred rent non-current		11,052
Operating lease liabilities, net of current portion	44,050
Other non-current liabilities	14,395	243
Total liabilities	127,327	96,821
Commitments and contingencies (Note 6)
Shareholders’ equity:
Common shares, CHF 0.03 par value, 103,901,006 and 90,343,803 shares authorized at December 31, 2019 and 2018, respectively, 61,034,025 and 52,160,798 shares issued at December 31, 2019 and 2018, respectively, 60,783,799 and 51,852,862 shares outstanding at December 31, 2019 and 2018, respectively.	1,847	1,584
Treasury shares, at cost, 250,226 and 307,936 shares at December 31, 2019 and 2018, respectively	(63)	(57)
Additional paid-in capital	1,162,345	682,245
Accumulated deficit	(224,711)	(291,569)
Accumulated other comprehensive income (loss)	7	(8)
Total shareholders' equity	939,425	392,195
Total liabilities and shareholders’ equity	$ 1,066,752	$ 489,016

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) $ in Thousands	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)shares
Statement Of Financial Position [Abstract]
Accounts receivable, related party amount, current	$ 0	$ 88
Prepaid expenses and other current assets, related party amount	0	3,417
Accrued expenses related party amount, current	0	1,700
Deferred revenue current related party amount	0	102
Deferred revenue non-current related party amount	$ 0	$ 57,780
Common stock, shares authorized | shares	103,901,006	90,343,803
Common stock, shares issued | shares	61,034,025	52,160,798
Common stock, shares outstanding | shares	60,783,799	51,852,862
Treasury stock, shares | shares	250,226	307,936

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Collaboration revenue	[1]	$ 289,590	$ 3,124	$ 40,997
Operating expenses:
Research and development	[2]	179,362	113,773	69,800
General and administrative		63,488	48,294	35,845
Total operating expenses		242,850	162,067	105,645
Income (loss) from operations		46,740	(158,943)	(64,648)
Other income (expense):
Loss from equity method investment		(5,467)	(4,275)	(1,763)
Other income (expense), net		26,033	(1,210)	(197)
Total other income (expense), net		20,566	(5,485)	(1,960)
Net income (loss) before income taxes		67,306	(164,428)	(66,608)
Provision for income taxes		(448)	(553)	(1,749)
Net income (loss)		66,858	(164,981)	(68,357)
Foreign currency translation adjustment		15	(22)	40
Comprehensive income (loss)		$ 66,873	$ (165,003)	$ (68,317)
Net income (loss) per share attributable to common shareholders— basic		$ 1.23	$ (3.44)	$ (1.71)
Weighted-average common shares outstanding used in net income (loss) per share attributable to common shareholders—basic		54,392,304	47,964,368	40,057,365
Net income (loss) per share attributable to common shareholders— diluted		$ 1.17	$ (3.44)	$ (1.71)
Weighted-average common shares outstanding used in net income (loss) per share attributable to common shareholders—diluted		56,932,798	47,964,368	40,057,365
[1]	Including the following amounts of revenue from a related party, see Note 7
[2]	Including the following amounts of research and development from a related party, see Note 7

Consolidated Statements of Op_2

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenue from related party	$ 746	$ 3,124	$ 4,760
Research and development expense with a related party	$ 14,459	$ 23,982	$ 4,523

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	ViaCyte [Member]	Common Shares [Member]	Common Shares [Member]ViaCyte [Member]	Treasury Shares [Member]	Treasury Shares [Member]ViaCyte [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]ViaCyte [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2016	$ 232,846		$ 1,216				$ 288,739		$ (57,083)	$ (26)
Beginning balance (in shares) at Dec. 31, 2016			39,719,434		444,873
Vesting of restricted shares	59		$ 1				58
Vesting of restricted shares (in shares)			33,519
Exercise of vested options, value	2,608		$ 23				2,585
Exercise of vested options (in shares)			839,295
Stock-based compensation expense	20,636						20,636
Other comprehensive income (loss)	40									40
Net income (loss)	(68,357)								(68,357)
Ending balance at Dec. 31, 2017	187,832		$ 1,240				312,018		(125,440)	14
Ending balance (in shares) at Dec. 31, 2017			40,592,248		444,873
Cumulative effect of ASC 606 adoption | ASU 2014-09 [Member]	(1,148)								(1,148)
Issuance of common stock, net of issuance costs	307,053		$ 311				306,742
Issuance of common stock, net of issuance costs (in shares)			9,960,526
Vesting of restricted shares	113		$ 1				112
Vesting of restricted shares (in shares)			38,761
Exercise of vested options, value	8,563		$ 26				8,537
Exercise of vested options (in shares)			946,131		(36,253)
Repurchase of treasury shares	(57)				$ (57)
Repurchase of treasury shares (in shares)			(64,952)		64,952
Issuance of shares to ViaCyte		$ 15,582		$ 6				$ 15,576
Issuance of shares to ViaCyte (in shares)				380,148		(165,636)
Stock-based compensation expense	39,260						39,260
Other comprehensive income (loss)	(22)									(22)
Net income (loss)	(164,981)								(164,981)
Ending balance at Dec. 31, 2018	392,195		$ 1,584		$ (57)		682,245		(291,569)	(8)
Ending balance (in shares) at Dec. 31, 2018			51,852,862		307,936
Issuance of common stock, net of issuance costs	414,789		$ 230				414,559
Issuance of common stock, net of issuance costs (in shares)			7,704,068		(47,297)
Vesting of restricted shares	43		$ 2				41
Vesting of restricted shares (in shares)			68,009
Exercise of vested options, value	$ 16,001		$ 31		$ (6)		15,976
Exercise of vested options (in shares)	1,180,644		1,158,860		(10,413)
Stock-based compensation expense	$ 49,524						49,524
Other comprehensive income (loss)	15									15
Net income (loss)	66,858								66,858
Ending balance at Dec. 31, 2019	$ 939,425		$ 1,847		$ (63)		$ 1,162,345		$ (224,711)	$ 7
Ending balance (in shares) at Dec. 31, 2019			60,783,799		250,226

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019SFr / shares	Dec. 31, 2018SFr / shares	Dec. 31, 2017SFr / shares
Common shares, par value | SFr / shares			SFr 0.03	SFr 0.03
Stock Options [Member]
Issuance costs | $	$ 0.3	$ 0.4
Common Shares [Member]
Issuance costs | $	$ 25.1	$ 23.8
Common shares, par value | SFr / shares			SFr 0.03	SFr 0.03	SFr 0.03

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net income (loss)	$ 66,858	$ (164,981)	$ (68,357)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	4,725	3,519	3,024
Equity-based compensation	44,057	34,985	18,873
Loss from equity method investment in Casebia	5,467	4,275	1,763
Non-cash expense related to ViaCyte transaction		15,582
Gain from consolidation of Casebia	(16,000)
Other income, non-cash		(169)	(9)
Changes in:
Accounts receivable	(11)	2,538	531
Prepaid expenses and other assets	(32,618)	(3,342)	(4,117)
Accounts payable and accrued expenses	5,025	12,110	(831)
Deferred revenue	(45,146)	(296)	(20,718)
Deferred rent		(709)	(522)
Operating lease assets and liabilities	(663)
Other liabilities, net	24,983	249	270
Net cash provided by (used in) operating activities	56,677	(96,239)	(70,093)
Investing activities
Purchase of property and equipment	(6,684)	(2,773)	(7,814)
Net cash and restricted cash received in connection with the acquisition of Casebia	8,009
Purchase of available for sale debt security			(500)
Net cash provided by (used in) investing activities	1,325	(2,773)	(8,314)
Financing activities
Proceeds from issuance of common shares, net of issuance costs	415,019	307,053
Proceeds from exercise of options, net of issuance costs	15,964	8,938	2,608
Repurchase of treasury shares		(57)
Net cash provided by financing activities	430,983	315,934	2,608
Effect of exchange rate changes on cash	15	(22)	41
Increase in cash	489,000	216,900	(75,758)
Cash, cash equivalents and restricted cash, beginning of period	459,812	242,912	318,670
Cash, cash equivalents and restricted cash, end of period	948,812	459,812	242,912
Supplemental disclosure of non-cash investing and financing activities
Property and equipment purchases in accounts payable and accrued expenses	1,811	334
Stock option issuance costs included in accrued expenses	$ 295	$ 375
Costs for proposed supplemental offering in accounts payable and accrued expenses			$ 290

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation to amounts within the consolidated balance sheets
Cash and cash equivalents	$ 943,771	$ 456,649	$ 239,758
Restricted Cash	5,041	3,163	3,154
Total	$ 948,812	$ 459,812	$ 242,912	$ 318,670

Organization and Operations

Organization and Operations	12 Months Ended
	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Operations	1. Organization and Operations CRISPR Therapeutics AG (“CRISPR” or the “Company”) was incorporated on October 31, 2013 in Basel, Switzerland. The Company was established to translate CRISPR/Cas9, a genome editing technology, into transformative gene-based medicines for the treatment of serious human diseases. The foundational intellectual property underlying the Company’s operations was licensed to the Company in April 2014. The Company devotes substantially all of its efforts to product research and development activities, initial market development and raising capital. The Company’s principal offices are in Zug, Switzerland and operations are in Cambridge, Massachusetts. The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any drug product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and ability to transition from pilot-scale manufacturing to large-scale production of products. The Company had an accumulated deficit of $224.7 million as of December 31, 2019 and has financed its operations to date from a series of preferred shares and convertible loan issuances, proceeds obtained from its initial public offering, subsequent public offerings of its common shares, as well as upfront fees and milestones received under its collaboration and joint venture arrangements. The Company will require substantial additional capital to fund its research and development and ongoing operating expenses. As of December 31, 2019, the Company had cash and cash equivalents of $943.8 million. While the Company had net income of $66.9 million for the year ended December 31, 2019, the Company has a history of recurring losses and expects to continue to incur losses for the foreseeable future. The Company expects its cash and cash equivalents will be sufficient to fund current planned operations for at least the next twenty-four months.

Summary of Significant Accounti

Summary of Significant Accounting Policies and Basis of Presentation	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies and Basis of Presentation	2. Summary of Significant Accounting Policies and basis of presentation Basis of Presentation and Use of Estimates The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly-owned subsidiaries as of December 31, 2019. All intercompany accounts and transactions have been eliminated. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board. Prior to December 13, 2019, the Company accounted for its 50% investment in Casebia Therapeutics, Limited Liability Partnership (“Casebia”) under the equity method. As described in Note 7, on December 13, 2019, Casebia became a fully-owned subsidiary and, as a result, the Company consolidated Casebia’s financial results from that date forward. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, revenue recognition, equity-based compensation expense and reported amounts of expenses during the period. Significant estimates in these consolidated financial statements have been made in connection with revenue recognition and equity-based compensation expense. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Certain items in the prior year’s condensed consolidated financial statements have been reclassified to conform to the current presentation. As a result, no subtotals in the prior year condensed consolidated financial statements were impacted. Segment Information The Company and the Company’s chief operating decision maker, namely, the chief executive officer, view the Company’s operations and manage its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology. Foreign Currency Translation and Transactions The majority of the Company’s operations occur in entities that have the U.S. dollar as their functional currency. Non-U.S. dollar denominated functional currency subsidiaries have assets and liabilities translated into U.S. dollars at rates of exchange in effect at the end of the year. Revenue and expense amounts are translated using the average exchange rates for the period. Net unrealized gains and losses resulting from foreign currency translation are included in “Accumulated other comprehensive income (loss).” Net foreign currency exchange transaction gains or losses are included in “Other income (expense), net” on the Company’s consolidated statement of operations, the impact of which is not significant. Cash and Cash Equivalents The Company considers all highly liquid investments with maturities of three months or less from the purchase date to be cash equivalents. As of December 31, 2019 and 2018, the Company had $943.8 million and $456.6 million in cash equivalents, respectively. Restricted Cash As of December 31, 2019 and 2018, the Company had $5.0 million and $3.2 million, respectively, in restricted cash representing letters of credit securing the Company’s obligations under certain leased facilities in Cambridge, Massachusetts, as well as certain credit card arrangements. The letters of credit are secured by cash held in a restricted depository account. Other Receivables Other receivables of $4.1 million and $3.4 million at December 31, 2019 and 2018, respectively, consists of receivables from Vertex and are included with prepaid and other current assets in the consolidated balance sheet. These amounts represent the balance due from the portion of our arrangement accounted for under ASC 808, Collaborative Arrangements Concentrations of Credit Risk and Off-balance Sheet Risk Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash. The Company’s cash is held in accounts with financial institutions that management believes are creditworthy. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no financial instruments with off-balance sheet risk of loss. Fair Value of Financial Instruments The Company has certain financial assets and liabilities recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements: Level 1 — Quoted prices in active markets that are accessible at the market date for identical unrestricted assets or liabilities. Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs for which all significant inputs are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying amount of accounts receivable, other receivables, accounts payable and accrued expenses as reported on the consolidated balance sheets as of December 31, 2019 and 2018, approximate fair value, due to the short-term duration of these instruments. Property and Equipment Property and equipment are recorded at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Asset Estimated useful life Computer equipment 3 years Furniture, fixtures and other 5 years Laboratory equipment 5 years Leasehold improvements Shorter of useful life or remaining lease term Impairment of Long-lived Assets The Company reviews long-lived assets when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparison of the book values of the assets to future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets. Revenue Recognition Effective January 1, 2018, the Company adopted ASC Topic 606, Revenue from Contracts with Customers by recognizing the cumulative effect of initially applying ASC 606 as an adjustment to the opening balance of equity at January 1, 2018. The reported results for 2019 and 2018 reflect the application of ASC 606 guidance while the reported results for 2017 were prepared under the guidance of ASC 605, Revenue Recognition (“ASC 605”). In connection with adopting ASC 606, t he Company elected a practical expedient and applied ASC 606 only to contracts that were not completed at the date of initial application. In addition, the Company applied the practical expedient in ASC 606-10-65-1 in identifying the satisfied and unsatisfied performance obligations, determining the transaction price and allocating the transaction price under the practical expedient in ASC 606 ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases and collaboration arrangements. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: 1) Identify the contract with the customer A contract with a customer exists when (i) the Company enters into an enforceable contract with a customer that defines each party’s rights regarding the goods or services to be transferred and identifies the related payment terms, (ii) the contract has commercial substance and (iii) the Company determines that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration. 2) Identify the performance obligations in the contract Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct, whereby the customer can benefit from the good or service either on its own or together with other available resources, and are distinct in the context of the contract, whereby the transfer of the good or service is separately identifiable from other promises in the contract. To the extent a contract includes multiple promised goods and services, the Company must apply judgment to determine whether promised goods and services are capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation. 3) Determine the transaction price The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration such as research, development, regulatory and commercial milestones, the Company determines if it is probable that it will receive such amounts and there is no risk of a significant revenue reversal. When the Company cannot conclude that receipt of such amounts is probable, the Company constrains the related variable consideration resulting in its exclusion from transaction consideration. In determining the portion of the transaction consideration to be constrained, the Company considers the probability and uncertainty that the related research, developmental, regulatory and commercial milestones will be achieved given the nature of research and clinical development and the stage of the underlying programs. This assessment is performed at each reporting period. In making this evaluation, the Company considers both internal and external information available, including information from industry publications and other relevant factors. Changes to the constraint of variable consideration can have a material effect on the amount of revenue recognized in the period. 4) Allocate the transaction consideration to performance obligations in the contract If the contract contains a single performance obligation, the entire transaction consideration is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction consideration to each performance obligation on a relative standalone selling price basis unless the transaction consideration is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices. In determining these estimated standalone selling prices, the Company makes a number of significant judgements including, for licenses, management’s assumptions regarding probability weighted projected discounted cash flows for each of the collaboration development programs. The estimated standalone selling prices are sensitive to changes in assumptions, such as probabilities of scientific success, discount rate and certain assumptions that form the basis of forecasted cash flows. In developing these assumptions, management considers both internal and external available, . Changes to these assumptions can have a material effect on the allocation of the transaction consideration to performance obligations, as well as the amount and timing of revenue recognized. 5) Recognize revenue when or as the Company satisfies a performance obligation The Company satisfies performance obligations over time or at a point in time, depending on the nature of the performance obligation. Revenue is recognized over time if the customer simultaneously receives and consumes the benefits provided by the entity’s performance, the entity’s performance creates or enhances an asset that the customer controls as the asset is created or enhanced, or the entity’s performance does not create an asset with an alternative use to the entity and the entity has an enforceable right to payment for performance completed to date. If the entity does not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring the control of a promised good or service to a customer. Contract Balances The Company recognizes a contract asset when the Company transfers goods or services to a customer before the customer pays consideration or before payment is due, excluding any amounts presented as a receivable (i.e. accounts receivable). A contract asset is an entity’s right to consideration in exchange for goods or services that the entity has transferred to a customer. The contract liabilities (i.e. deferred revenue) primarily relate to contracts where we have received payment, but we have not yet satisfied the related performance obligations. The Company recorded contract assets of $25.7 million and $0.0 million as of December 31, 2019 and 2018, respectively. Deferred revenue as of December 31, 2019 and 2018 was $12.7 million and $57.8 million. The change in contract assets and deferred revenue is related to the collaboration agreement with Vertex described in Note 7. Collaboration Arrangements The Company records the elements of its collaboration agreements that represent joint operating activities in accordance with ASC 808, Collaborative arrangements The Company evaluates the proper presentation of the commercial activities and the profit and loss sharing associated with the collaboration agreements. ASC 808 states that when payments between parties in a collaborative arrangement are not within the scope of other authoritative accounting literature, the income statement classification should be based on the nature of the arrangement, the nature of its business operations and the contractual terms of the arrangement. To the extent that these payments are not within the scope of other authoritative accounting literature, the income statement classification for the payments shall be based on an analogy to authoritative accounting literature or if there is no appropriate analogy, a reasonable, rational and consistently applied accounting policy election. Research and Development Expenses Research and development costs are charged to expense as costs are incurred in performing research and development activities, including salaries and benefits, facilities costs, overhead costs, clinical study and related clinical manufacturing costs, license and milestone fees, contract services and other related costs. Research and development costs, including up-front fees and milestones paid to collaborators, are also expensed as incurred. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense. The Company accrues costs for clinical trial activities based upon estimates of the services received and related expenses incurred that have yet to be invoiced by the contract research organizations, clinical study sites, laboratories, consultants or other clinical trial vendors that perform the activities. The Company recognizes the reimbursement associated with collaborative activities to its collaborative partners as research and development expense in the period the services are provided. Leases Effective January 1, 2019, the Company adopted ASC 842, Leases Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and short-term and long-term lease liabilities, as applicable. The Company does not have financing leases. Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. Prospectively, the Company will adjust the right-of-use assets for straight-line rent expense or any incentives received and remeasure the lease liability at the net present value using the same incremental borrowing rate that was in effect as of the lease commencement or transition date. The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. Assumptions made by the Company at the commencement date are re-evaluated upon occurrence of certain events, including a lease modification. A lease modification results in a separate contract when the modification grants the lessee an additional right of use not included in the original lease and when lease payments increase commensurate with the standalone price for the additional right of use. When a lease modification results in a separate contract, it is accounted for in the same manner as a new lease. Equity Based Compensation Expense The Company’s share-based compensation programs grant awards that have included stock options, restricted stock units and restricted stock awards. Grants are awarded to employees and non-employees, including directors. The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments to employees and non-employee directors, including grants of employee stock options and restricted stock units and modifications to existing stock options, to be recognized in the consolidated statements of operations and comprehensive income (loss) based on their fair values. The Company uses the Black-Scholes option pricing model to determine the fair value of options granted. The Company accounts for forfeitures as they occur instead of estimating forfeitures at the time of grant and revising those estimates in subsequent periods if actual forfeitures differ from its estimates. Stock-based compensation expense recognized in the financial statements is based on awards for which performance or service conditions are expected to be satisfied. Prior to the adoption of ASU No. 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting The Company’s stock-based awards are subject to service or performance-based vesting conditions. Compensation expense related to awards to employees, directors and non-employees with service-based vesting conditions is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term. Compensation expense related to awards to employees and non-employees with performance-based vesting conditions is recognized based on the grant date fair value over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable. The Company expenses restricted stock unit awards to employees based on the fair value of the award on a straight-line basis over the associated service period of the award. The Company estimates the fair value of its option awards to employees, directors and non-employees using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including (i) the expected stock price volatility, (ii) the calculation of expected term of the award, (iii) the risk-free interest rate and (iv) expected dividends. Due to the lack of complete company-specific historical and implied volatility data for the full expected term of the stock-based awards, the Company bases its estimate of expected volatility on a representative group of publicly traded companies in addition to its own volatility data. For these analyses, the Company selected companies with comparable characteristics to its own, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected life of the stock-based awards. The Company computes historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. The Company has estimated the expected term of its employee stock options using the “simplified” method, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option, due to its lack of sufficient historical data. The risk-free interest rates for periods within the expected term of the option are based on the U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid, and does not expect to pay, dividends in the foreseeable future. Patent Costs Costs to secure and prosecute patent applications and other legal costs related to the protection of the Company’s intellectual property are expensed as incurred and are classified as general and administrative expenses in the Company’s consolidated statements of operations. Income Taxes Income taxes are recorded in accordance with ASC Topic 740, Income Taxes The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2019, and 2018, the Company does not have any significant uncertain tax positions. The Company’s practice is to recognize interest and/or penalties related to income tax matters in income tax expense. See Note 12 for further details. Comprehensive Income (Loss) Comprehensive income (loss) consists of net income or loss and other comprehensive income (loss). Other comprehensive income (loss) consists of foreign currency translation adjustments. Variable Interest Entities The Company reviews each legal entity formed by parties related to the Company to determine whether or not the Company has a variable interest in the entity and whether or not the entity would meet the definition of a variable interest entity (“VIE”) in accordance with ASC Topic 810, Consolidation If the Company determines it is the primary beneficiary of a VIE that meets the definition of a business, the Company measures the assets, liabilities and noncontrolling interests of the newly consolidated entity at fair value in accordance with ASC Topic 805, Business Combinations In February 2016, Casebia, was formed in the United Kingdom. In March 2016, upon consummation of the joint venture (“JV”), Bayer Healthcare LLC and certain of its affiliates (“Bayer”) and the Company each received a 50% equity interest in the entity in exchange for their contributions to the entity. The Company determined that Casebia was considered a VIE and concluded that it is not the primary beneficiary of the VIE. As such, the Company has not historically consolidated Casebia’s results into the consolidated financial statements. As described in Note 7, on December 13, 2019, Casebia became a fully-owned subsidiary and, as a result, the Company consolidated Casebia’s financial results accordingly from that point forward. Net Income (Loss) Per Share Attributable to Common Shareholders Basic net income (loss) per share is calculated by dividing net income (loss) attributable to common shareholders by the weighted-average number of common shares outstanding during the period. Diluted net income per share is calculated by dividing the net income attributable to common shareholders by the weighted-average number of common equivalent shares outstanding for the period, including any dilutive effect from outstanding stock options and restricted stock units using the treasury stock method. See Note 10 for further details. New Accounting Pronouncements – Recently Adopted Leases As discussed above, the Company adopted ASC 842, using the required modified retrospective approach, effective January 1, 2019. The Company chose to apply the transition provisions as of the period of adoption. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which, among other things, allowed the Company to carry forward the historical lease classification. In addition, the Company elected the practical expedient not to apply the recognition requirements in the lease standard to short-term leases (a lease that at commencement date has a lease term of 12 months or less and does not contain a purchase option that it is reasonably certain to exercise) and the practical expedient that permits lessees to make an accounting policy election (by class of underlying asset) to account for each separate lease component of a contract and its associated non-lease components as a single lease component. The adoption of the new standard resulted in the recording net lease assets and lease liabilities of $26.1 million and $37.6 million, respectively, as of January 1, 2019. The difference between the additional lease assets and lease liabilities is primarily due to the change in classification of lease incentives from liabilities to a reduction in our net lease assets. The standard had no impact on our net loss or cash flows. Impact of Adopting ASC 842 on the Financial Statements January 1, 2019 Prior to ASC 842 Adoption ASC 842 Adjustment January 1, 2019 As Adjusted Consolidated Balance Sheet Data (in thousands): Prepaid expenses and other current assets (1) $ 9,658 $ (553 ) $ 9,105 Operating lease assets (2) $ — $ 26,087 $ 26,087 Deferred rent (3)(4) $ 1,026 $ (1,026 ) $ — Deferred rent non-current (3) $ 11,052 $ (11,052 ) $ — Operating lease liabilities (5) $ — $ 4,930 $ 4,930 Non-current operating lease liabilities (5) $ — $ 32,682 $ 32,682 (1) Represents reclassification of prepaid rent to operating lease assets. (2) Represents capitalization of operating lease assets and reclassification of equipment licenses from prepaid expenses to operating lease assets, offset by reclassification of deferred rent to operating lease assets. (3) Represents reclassification of deferred rent and tenant incentives to operating lease assets. (4) As of December 31, 2018, the deferred rent balance was $1,202, which included $176 of sublease income received prior to year-end but not due until January 1, 2019. (5) Represents recognition of operating lease liabilities. New Accounting Pronouncements – Not Yet Adopted Credit Losses In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 362): Measurement of Credit Losses on Financial Statements , Financial Instruments-Overall

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Property and Equipment, net	3. Property and Equipment, net Property and equipment, net, consists of the following (in thousands): As of December 31, 2019 2018 Computer equipment $ 727 $ 443 Furniture, fixtures, and other 3,215 2,453 Laboratory equipment 16,640 8,964 Leasehold improvements 21,400 13,776 Construction work in process 1,394 239 Total property and equipment, gross 43,376 25,875 Accumulated Depreciation (12,046 ) (7,375 ) Total property and equipment, net $ 31,330 $ 18,500 Depreciation expense for the year ended December 31, 2019, 2018, and 2017 was $4.7 million, $3.5 million, and $3.0 million, respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued Expenses	4. Accrued Expenses Accrued expenses consist of the following (in thousands): As of December 31, 2019 2018 Payroll and employee-related costs $ 15,229 $ 7,321 Research costs 9,434 7,973 Licensing fees 750 625 Professional fees 2,040 1,848 Intellectual property costs 2,311 2,193 Accrued property and equipment 407 294 Other 9 598 Total $ 30,180 $ 20,852

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases	5. Leases In June 2015, the Company entered into a lease agreement for the lease of research facility space in Cambridge, Massachusetts, with a commencement date of November 15, 2015 (the “2015 Lease”). The lease expires in February 2022 With the adoption of ASC 842, the Company has recorded a right-of-use asset and corresponding lease liability. In May 2016, the Company entered into a sublease agreement for its primary office and research facility in Cambridge, Massachusetts, with a commencement date of December 23, 2016 (the “2016 Sublease”). The sublease expires in December 2026 five-year With the adoption of ASC 842, the Company has recorded a right-of-use asset and corresponding lease liability. The right-of-use asset and corresponding lease liability does not include the additional five-year In May 2019, the Company entered into a lease agreement for office facility space in Cambridge, Massachusetts, with a commencement date of June 1, 2019 (the “2019 Lease”). The lease expires in November 2026 five-year The right-of-use asset and corresponding lease liability does not include the additional five-year In December 2019, Casebia became a wholly-owned subsidiary of the Company. In connection therewith, Casebia assigned its sublease for an office and research facility in Cambridge, Massachusetts (“2019 Sublease”) to the Company. The sublease expires in March 2024 five-year five-year as the Company is not reasonably certain not to exercise that option In addition, the Company rents certain office space in Zug, Switzerland, on a short-term basis for which a right-of-use asset and liability are not recorded, in accordance with the practical expedient elected. The Company has embedded leases in certain research and license agreements for which the Company has recorded a right of use asset and liability. These arrangements are not significant in comparison to the Company’s total operating lease assets and liabilities. In addition, the Company has identified certain short-term leases embedded within its manufacturing contracts which are not recorded on the Company’s balance sheet in accordance with the practical expedient elected. The Company identified and assessed the following estimates in recognizing the right-of-use asset and corresponding liability: • Expected lease term : The expected lease term for those leases commencing prior to January 1, 2019 did not change with the adoption of ASC 842. The expected lease term for leases commencing after the adoption of ASC 842 includes noncancelable lease periods and, when applicable, periods covered by an option to extend the lease if the Company is reasonably certain to exercise that option, as well as periods covered by an option to terminate the lease if the Company is reasonably certain not to exercise that option. • Incremental borrowing rate : As the discount rates in the Company’s lease are not implicit, the Company estimated the incremental borrowing rate based on the rate of interest the Company would have to pay to borrow a similar amount on a collateralized basis over a similar term. The following table summarizes the lease assets and liabilities as of December 31, 2019 (in thousands): As of December 31, 2019 Assets Operating lease assets $ 41,502 Total lease assets 41,502 Liabilities Current Operating lease liabilities 8,489 Non-current Operating lease liabilities, net of current portion 44,050 Total lease liabilities $ 52,539 The following table summarizes operating lease costs included in research and development and general and administrative expense, as well as sublease income for the twelve months ended December 31, 2019 (in thousands): Twelve Months Ended December 31, 2019 Operating lease costs $ 8,067 Short-term lease costs 4,554 Variable lease costs 4,282 Sublease income (525 ) Net lease cost $ 16,378 The following table summarizes the maturity of undiscounted payments due under lease liabilities and the present value of those liabilities as of December 31, 2019 (in thousands): Total 2020 $ 13,963 2021 11,824 2022 10,167 2023 10,269 2024 8,308 Thereafter 15,678 Total $ 70,209 Present value adjustment (17,670 ) Present value of lease liabilities $ 52,539 The following table summarizes the lease term and discount rate as of December 31, 2019 : As of December 31, 2019 Weighted-average remaining lease term (years) Operating leases 6.0 Weighted-average discount rate Operating leases 9.9 % The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the twelve months ended December 31, 2019 (in thousands): Twelve Months Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities $ 8,420 Operating cash flows from operating leases $ 8,420

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Intellectual Property Agreements Patent Assignment Agreement In November 2014, the Company entered into a patent assignment agreement with Dr. Emmanuelle Charpentier, Dr. Ines Fonfara, and Vienna (collectively, the “Assignors”), pursuant to which the Company was assigned all rights, title and interest in and to certain patent rights claimed in the U.S. Patent Application No.61/905,835. As a result, the Assignors are entitled to receive certain low single digit clinical milestone payments and low single digit royalties based on annual net sales of licensed products and licensed services by the Company, its affiliates and sublicensees. Charpentier License Agreements In April 2014, the Company entered into certain technology license agreements with Dr. Charpentier pursuant to which the Company licensed certain intellectual property rights under joint ownership from Dr. Charpentier to develop and commercialize products for the treatment or prevention of human diseases. In connection therewith, Dr. Charpentier is entitled to receive nominal clinical milestone payments, low single digit percentage of sublicensing payments received under any sublicense agreement with a third party, and low single-digit percentage royalties based on annual net sales of licensed products and services by the Company and its affiliates and sublicensees. During the years ended December 31, 2019, 2018 and 2017, the Company paid an immaterial amount of fees to Dr. Charpentier, which were recorded as research and development expense. Research, Manufacturing and License Agreements The Company has engaged several research institutions and companies to identify new delivery strategies and applications of the gene-editing technology. The Company is also a party to a number of research license agreements which require significant upfront payments, and may require future royalty payments and potential milestone payments from time to time. In addition, the Company is also a party to intellectual property agreements, which require maintenance and milestone payments from time to time. Further, the Company is a party to a number of manufacturing agreements that require upfront payments for the future performance of services. In association with these agreements, on a product by product basis, the counterparties are eligible to receive up to low eight-digit potential payments upon specified research, development and regulatory milestones. In addition, on a product by product basis, the counterparties are eligible to receive potential commercial milestone payments based on specified annual sales thresholds. The potential payments are low-single digit percentages of the specified annual sales thresholds. The counterparties are also eligible to receive low single -digit royalties on future net sales. Under certain circumstances and if certain contingent future events occur, Vertex is eligible to receive up to $395.0 million in potential specified research, development, regulatory and commercial milestones and tiered single-digit royalties on future net sales. Refer to Note 7 for further discussion on the Company’s arrangements with Vertex. Litigation The Company licenses a U.S. patent application from Dr. Charpentier that was subject to interference proceedings declared by the Patent Trial and Appeal Board (“PTAB”) of the U.S. Patent and Trademark Office (“USPTO”). Following motions by the parties and other procedural matters, the PTAB concluded in February 2017 that the declared interference should be dismissed because the claim sets of the two parties were not directed to the same patentable invention in accordance with the PTAB’s two-way test for patent interferences. In April 2017, Dr. Charpentier, the Regents of the University of California (“UC”), and the University of Vienna (collectively “UC”) appealed the PTAB decision to the U.S. Court of Appeals for the Federal Circuit (“Federal Circuit”). In the appeal, UC asked the court to review and reverse of the PTAB’s February 2017 decision, which terminated the interference without determining which inventors actually invented the use of the CRISPR/Cas9 genome editing technology in eukaryotic cells. The Federal Circuit conducted a hearing on the appeal on April 30, 2018. On September 10, 2018, the Federal Circuit affirmed the PTAB’s decision to terminate the interference proceeding. In June 2019, we received notification that the USPTO initiated a new interference proceeding at the PTAB, which the PTAB redeclared in August 2019. The ‘115 interference involves fourteen (14) pending U.S. patent applications co-owned by the CVC Group and thirteen (13) patents and a patent application owned by the Broad. Specifically, the PTAB declared the ‘115 interference between the CVC Group’s pending U.S. Patent Application Nos. 15/947,680; 15/947,700; 15/947,718; 15/981,807; 15/981,808; 15/981,809; 16/136,159; 16/136,165; 16/136,168; 16/136,175; 16/276,361; 16/276,365; 16/276,368; and 16/276,374, and the Broad’s U.S. Patent Nos. 8,697,359; 8,771,945; 8,795,965; 8,865,406; 8,871,445; 8,889,356; 8,895,308; 8,906,616; 8,932,814; 8,945,839; 8,993,233; 8,999,641; 9,840,713, and U.S. Patent Application No. 14/704,551. This list includes the same twelve Broad patents and application that were involved in the ‘048 interference. In contrast, none of the issued U.S. patents the CVC Group owns are subject to this proceeding. The CVC Group’s inventions that are the subject of the ‘115 interference were first filed with the USPTO in May of 2012, while the Broad filed its first application seven months later in December of 2012. However, the 14 CVC Group patent applications that are involved in the ‘115 interference are continuing patent applications that were filed in 2018 and claim priority to the CVC Group’s original 2012 filing, while the Broad’s involved patents and patent application were filed between 2013 and 2015. Because the PTAB accorded neither party the benefit of any of its first filing dates, but instead accorded only the benefit of the actual filing dates of the involved patents and patent applications, the CVC Group was by default named the Junior Party. Both parties have filed motions requesting the benefit of their earliest priority dates (CVC in May of 2012 and the Broad in December of 2012) during the interference proceeding In February 2018, several parties filed oppositions in the European Patent Office to the grant of the Company’s in-licensed European patent. Opposition proceedings can lead to the revocation of a patent in its entirety; the maintenance of the patent as granted, or the maintenance of a patent in amended form. Opposition proceedings typically take years to resolve, including the time taken by appeals that can be filed by any of the parties. The Company cannot guarantee the outcome of the oppositions to its in-licensed European patent, and an adverse result could preclude the Company from enforcing its rights in Europe against third parties. On December 15, 2016, the Company entered into a Consent to Assignments, Licensing and Common Ownership and Invention Management Agreement (the “Invention Management Agreement”) with the Regents of the University of California, University of Vienna, Dr. Charpentier, Intellia Therapeutics, Inc. Caribou Biosciences, Inc., ERS Genomics Ltd. and one of our subsidiaries. Under the Invention Management Agreement, the Company is obligated to share costs related to patent maintenance, defense and prosecution. For the years ended December 31, 2019, 2018 and 2017, the Company incurred $2.9 million, $2.4 million and $1.2 million, respectively, in shared costs. The Company recorded accrued legal costs from the cost sharing of $1.5 million and $1.9 million as of December 31, 2019 and December 31, 2018, respectively. The Company is unable to predict the outcome of these matters and is unable to make a meaningful estimate of the amount or range of loss, if any, that could result from an unfavorable outcome . In addition to the above, in the ordinary course of business, the Company is from time to time involved in lawsuits, claims, investigations, proceedings, and threats of litigation relating to intellectual property, commercial arrangements, employment and other matters. While the outcome of those proceedings and claims cannot be predicted with certainty, the Company is not party to any legal or arbitration proceedings that may have significant effects on its financial position. It is not a party to any material proceedings in which any director, member of executive management or affiliate of the Company is either a party adverse to it or its subsidiaries or has a material interest adverse to it or its subsidiaries.

Significant Contracts

Significant Contracts	12 Months Ended
	Dec. 31, 2019
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 (the “2015 Collaboration Agreement”) with Vertex Pharmaceuticals Incorporated and certain of its subsidiaries (“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 (“Amendment No. 1”) and the Joint Development Agreement (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 (the “2019 Collaboration Agreement”) for the development and commercialization of products for the treatment of Duchenne Muscular Dystrophy (“DMD”) and Myotonic Dystrophy Type 1 (“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 future 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 (“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 (“Amendment No. 2”). Among other things, Amendment No. 2 modified certain definitions and provisions of the 2015 Collaboration Agreement to make them consistent with the 2019 Collaboration Agreement and set forth the number and identity of the collaboration targets under the 2015 Collaboration Agreement. The Company and Vertex agreed that one of the four remaining options under the 2015 Collaboration Agreement, as amended, would not be exercised; instead, the Company will reacquire the exclusive rights and will conduct research and development activities for the specified target. Vertex will have the option to co-develop and co-commercialize the specified target upon IND filing in exchange for payment of 50% of research and development costs incurred by the Company from the effective date of the agreement through IND filing. If Vertex does not exercise its option to co-develop and co-commercialize the specified target, Vertex is eligible to receive up to $395.0 million in potential specified research, development, regulatory and commercial milestones and tiered single-digit royalties on future net sales. In October 2019, Vertex exercised the remaining three options granted to it under the 2015 Collaboration Agreement to exclusively license the collaboration targets developed under the 2015 Collaboration Agreement, resulting in a payment of $30.0 million to the Company in the fourth quarter of 2019. Accounting for the Vertex Agreements The 2015 Collaboration Agreement, Amendment No. 1, and JDA are collectively the “2015 Agreements” and the 2019 Collaboration Agreement and Amendment No. 2. are collectively the “2019 Agreements.” The 2015 Collaboration Agreement, Amendment No. 1, Amendment No. 2, JDA and 2019 Collaboration Agreement are collectively the “Vertex Agreements.” The Vertex Agreements include components of a customer-vendor relationship as defined under ASC 606, , collaborative arrangements as defined under ASC 808 and research and development costs as defined under ASC 730, Research and Development 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 (“DMD License”); (ii) an exclusive license for worldwide rights for DM1 gene editing products (“DM1 License”); (iii) the performance of specified guide RNA research for DM1 (“DM1 R&D Services”); (iv) a material right representing the option to obtain a co-exclusive development and commercialization license for a specified target (“Specified Target Option”); (v) three material rights representing the option for up to three exclusive licenses to develop and commercialize the collaboration targets (“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 represents 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; and (v) variable consideration of $0.8 million which represents the Company’s estimate of payments from Vertex for DM1 R&D Services. The Company determined that all other possible variable consideration resulting from milestones and royalties discussed above was fully constrained as of December 31, 2019. 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 (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 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 associated 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 are 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. In addition, the Company recognized $30.0 million in revenue corresponding to the three $10.0 million payments made by Vertex to exercise the three options, the consideration for which, the Company determined relates specifically to the Company’s efforts to satisfy the respective performance obligations (material rights) and that allocating the amounts to those performance obligations (material rights) satisfies allocation objectives in ASC 606-10-32-28. The Company recognizes revenue related to the DM1 R&D Services over time as the services are rendered, which is expected to be over an 18-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 as of December 31, 2018 and 2017. 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 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 alloacted 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 ESSP’s 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, 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 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 During the years ended December 31, 2019, 2018 and 2017, the Company recognized $289.1 million, $0.6 million and $36.2 million of revenue related to the Vertex Agreements, respectively. The $289.1 million of revenue recognized for the year-ended December 31, 2019 was comprised of (i) revenue related to the DMD License and DM1 License of $202.4 million, which was recognized at the point in time in which the licenses were delivered, (ii) revenue related to the Collaboration Target Options material right of $76.7 million, which was recognized upon the exercise of the Collaboration Target Options by Vertex, (iii) revenue allocated to the waiving of Vertex’s material right associated with its option to a fourth exclusive license in connection with the Company’s reacquisition of exclusive rights to the specified target of $6.7 million, which was recognized at the point in time in which the option was waived, (iv) revenue recognized in connection with DM1 R&D Services of $0.1 million and (v) revenue recognized of $0.1 million related to both research and development services as well as the amortization of the non-exclusive research license under the 2015 Agreements. Additionally, the Company recognized revenue related to a one-time low seven-digit milestone payment upon the dosing of the second patient in a clinical trial with the initial product candidate in the third quarter of 2019. The $0.6 million in revenue recognized in 2018 was comprised of both research and development services as well as the amortization of the non-exclusive research license under the 2015 Agreements. The $36.2 million of revenue recognized in 2017 was comprised of primarily of (i) $30.3 million allocated to co-exclusive research license and a development and commercialization license to develop and commercialize each of the hemoglobinopathy and beta-globin targets under ASC 605, which was recognized in connection with the signing of the JDA in December 2017 and (ii) research and development services under the 2015 Agreements. As of December 31, 2019 and 2018, there was $0.9 million and $0.1 million of current deferred revenue related to the Vertex Agreements. As of December 31, 2019 and 2018, there was $11.8 million and $57.8 million of non-current deferred revenue related the Vertex Agreements. The transaction price allocated to the remaining performance obligations was $12.7 million. Milestones under the Vertex Agreements The Company has evaluated the milestones that may be received in connection with the Vertex Agreements. As discussed above, in connection with the Collaboration Target Options, the Company received $30.0 million in option exercise payments from Vertex in the fourth quarter of 2019. 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. In connection with the JDA, the Company 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. Revenue was recognized for this milestone in the third quarter of 2019, the point in time in which the milestone was both probable and achieved. The Company is eligible to receive potential future 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. As discussed above, the first research milestone of $25.0 million was included in the transaction price. This amount is recorded as a contract asset within prepaid expenses and other current assets on the condensed consolidated balance sheet. 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. With the exception of the first research milestone of $25.0 million, each of the remaining milestones are fully constrained as of December 31, 2019. There is uncertainty that the events to obtain the research and developmental milestones will be achieved given the nature of clinical development and the stage of the CRISPR/Cas9 technology. The remaining research, development and regulatory milestones will be constrained until it is probable that a significant revenue reversal will not occur. Commercial milestones and royalties relate predominantly to a license of intellectual property and are determined by sales or usage-based thresholds. The commercial milestones and royalties are accounted for under the royalty recognition constraint and will be accounted for as constrained variable consideration. The Company applies the royalty recognition constraint for each commercial milestone and will not recognize revenue for each until the subsequent sale of a licensed product (achievement of each) occurs. Accounting Analysis under ASC 808 In connection with the 2019 Agreements, the Company identified the following collaborative elements, which were unchanged as those identified with the 2015 Agreements and are accounted for under ASC 808: (i) development and commercialization services for shared products; (ii) R&D Services for follow-on products; and (iii) committee participation. The related impact of the cost sharing associated with research and development is included in research and development expense. Expenses related to services performed by the Company are classified as research and development expense. Payments received from Vertex for partial reimbursement of expenses are recorded as a reduction of research and development expense. During the years ended December 31, 2019, 2018 and 2017, the Company recognized $29.2 million, $20.2 million and $9.9 million of research and development expense related to the Vertex Agreements. Research and development expense for 2019, 2018 and 2017 is net of $15.9 million, $13.8 million and $0.0 million of reimbursements from Vertex, respectively. Accounting Analysis under ASC 730 In connection with the 2019 Vertex Agreements, the Company and Vertex agreed that one of the four remaining options under the 2015 Agreements, as amended, would not be exercised; instead, the Company will conduct research and development activities for a specified target. Vertex will have the option to co-develop and co-commercialize the specified target upon IND filing in exchange for payment of 50% of research and development costs incurred by the Company from the effective date of the agreement through IND filing. If Vertex does not exercise its option to do so within a specified time period, Vertex is eligible to receive up to $395.0 million in potential specified research, development, regulatory and commercial milestones and tiered single-digit royalties on future net sales. In connection therewith, the Company determined that in order for the Company to obtain the right to conduct research and development activities on the specified target, the Company had waived its right to receive an option exercise payment of $10.0 million from Vertex, which was included as non-cash consideration in the transaction price 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. Joint Venture 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 this 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 (“Retirement Agreement”), the Company and Bayer terminated their joint venture (“Joint Venture Termination Agreement”), and the Company and Bayer entered into a new option agreement (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 up to $22.0 million returned from Casebia operating cash less certain estimated interim operating expenses of $6.0 million, which is subject to potential post-closing adjustments, 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 will now be 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 (the “Option Payment”) to the Company that will become non-refundable once the parties execute a Co-Commercialization Agreement with respect to such optioned product. The Option Payment is payable only once with respect to the first time Bayer exercises an option under the 2019 Option Agreement. In addition, following Bayer’s exercise of its option and/or the execution of a 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 3 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, a

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Share Capital	8. Share Capital The Company had 103.9 million and 90.3 As of December 31, Type of Share Capital Conditional Capital 2019 2018 Common shares Registered share capital 61,037 52,268 Common shares Authorized share capital 19,246 17,577 Common shares Conditional share capital - Bonds or similar debt instruments 4,920 4,920 Common shares Conditional share capital - Employee benefit plans 18,698 15,579 Total 103,901 90,344 Included in registered share capital are 1,230,729 shares registered, which are held by the Company and its subsidiaries and are reserved for future issuance for financings. Common Share Issuances In October 2016, the Company sold 4.4 million common shares through an initial public offering (inclusive of shares sold pursuant to an overallotment option granted to the underwriters in connection with the offering) at a price of $14.00 per share for proceeds of $53.7 million, which were net of equity issuance costs of $8.3 million. Concurrent with the initial public offering, the Company sold 2.5 million common shares to Bayer BV in a private placement, at a price of $14.00 per share, resulting in aggregate net proceeds of $35.0 million. In January 2018, the Company sold 5.7 million common shares through an underwritten public offering (inclusive of shares sold pursuant to an overallotment option granted to the underwriters in connection with the offering) at a price of $22.75 per share for proceeds of $122.6 million, which were net of equity issuance costs of $8.2 million. In September 2018, the Company sold 4.2 million common shares through an underwritten offering at a price of $47.50 per share for proceeds of $184.5 million which were net of equity issuance costs In the first quarter of 2019, the Company began to sell securities under an Open Market Sale Agreement SM In November 2019, the Company sold 4.9 million common shares through an underwritten public offering (inclusive of shares sold pursuant to the exercise of the option to purchase additional shares granted to the underwriters in connection with the offering) at a price of $64.50 per share for proceeds of $294.4 million, which were net of equity issuance costs of $20.7 million. In addition, in August 2019, following the termination of the 2018 ATM by its terms, the Company entered into a new Open Market Sale Agreement SM The Common Shares have the following characteristics: Voting Rights The holders of Common Shares are entitled to one vote for each Common Share held at all meetings of shareholders. Dividends The holders of Common Shares are entitled to receive dividends, if and when resolved upon by the general meeting of shareholders based on a respective proposal by the Board of Directors and provided that the Company disposes of sufficient freely distributable reserves. As of December 31, 2019, no dividends have been declared or paid since the Company’s inception. Liquidation The holders of the Common Shares are entitled to share ratably in the Company’s assets available for distribution to shareholders in the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or upon the occurrence of a deemed liquidation event.

Equity-based Compensation

Equity-based Compensation	12 Months Ended
	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity-based Compensation	9. Equity-based Compensation Option and Grant Plans In April 2015, the Company’s shareholders approved the 2015 Stock Option and Grant Plan (the “2015 Plan”) and in July 2016, the Company’s shareholders approved the 2016 Stock Option and Incentive Plan (the “2016 Plan”). In May 2018, the Company’s shareholders approved the 2018 Stock Option and Incentive Plan (the “2018 Plan,” collectively, the “Plans”). Subsequent to the IPO, no further options were granted under the 2015 Plan. The Plans provide for the issuance of equity awards in the form of restricted shares, options to purchase Common Shares which may constitute incentive stock options (“ISOs”) or non-statutory stock options (“NSOs”), unrestricted stock unit grants, and qualified performance and market-based awards to eligible employees, officers, directors, non-employee consultants and other key personnel. Terms of the equity awards, including vesting requirements, are determined by the Company’s Board of Directors, subject to the provisions of the Plans. Options granted by the Company typically vest over four years and have a contractual life of ten years. Equity-Based Compensation Expense The Company recognized stock-based compensation expense totaling $49.5 million, $39.3 million, and $20.6 million during the years ended December 31, 2019, 2018 and 2017, respectively. Stock‑based compensation expense by classification within the consolidated statements of operations and comprehensive income (loss) is as follows (in thousands): Years Ended December 31, 2019 2018 2017 Research and development $ 23,273 $ 17,557 $ 8,800 General and administrative 20,784 17,428 10,073 Loss from equity method investment 5,467 4,275 1,763 Total $ 49,524 $ 39,260 $ 20,636 As of December 31, 2019, there was $96.2 million and $31.9 million of unrecognized compensation expense related to unvested stock options and restricted stock units, respectively, that is expected to be recognized over a weighted-average period of 2.8 and 2.3 years, respectively. Stock Options The fair value of each option issued to employees and non-employees was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions: Years Ended December 31, 2019 2018 2017 Options granted 2,832,784 2,209,597 2,999,847 Weighted-average exercise price $ 39.16 $ 51.73 $ 16.98 Weighted-average grant date fair value $ 24.57 $ 33.82 $ 11.16 Assumptions: Expected volatility 68.9 % 71.9 % 72.5 % Expected term (in years) 6.0 6.0 6.1 Risk-free interest rate 2.2 % 2.8 % 2.0 % Expected dividend yield 0.0 % 0.0 % 0.0 % The following table summarizes stock option activity under the Company’s equity award plans (intrinsic value in thousands): Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding at December 31, 2018 6,689,311 $ 25.42 8.3 $ 68,572 Granted 2,832,784 $ 39.16 Exercised (1,180,644 ) $ 14.91 Cancelled or forfeited (559,014 ) $ 35.35 Outstanding at December 31, 2019 7,782,437 $ 31.30 8.2 231,554 Exercisable at December 31, 2019 3,328,398 $ 24.07 7.4 $ 122,774 Vested and expected to vest at December 31, 2019 7,782,437 $ 31.30 8.2 $ 231,554 During 2019 and 2018, the Company did not grant awards subject to performance-based or market-based vesting conditions. As of December 31, 2019, options to purchase 883,695 Common Shares subject to performance-based vesting conditions were vested, as performance conditions were achieved, and there were 261,888 options to purchase Common Shares subject to performance-based vesting conditions outstanding. During 2017, the Company granted 150,000 options with market-based vesting conditions, of which 75% vest at the end of a three-year four-year The total intrinsic value (the amount by which the fair market value exceeded the exercise price) of stock options exercised during the year ended December 31, 2019, 2018 and 2017 was $42.2 million, $38.3 million and $12.3 million, respectively. Restricted Stock The following table summarizes the restricted stock activity under the Company’s equity award plans (shares in thousands): Shares Weighted- Average Grant Date Fair Value Unvested restricted common shares at December 31, 2018 327,342 $ 36.72 Granted 503,600 62.11 Vested (86,758 ) 20.38 Cancelled or forfeited (44,650 ) 44.50 Unvested restricted common shares at December 31, 2019 699,534 $ 56.53 During the years ended December 31, 2019, 2018 and 2017, the total fair value of restricted stock vested was $3.6 million, $11.3 million and $8.3 million, respectively. Award modifications During the years ended December 31, 2019, 2018 and 2017, the Company modified the terms of certain equity awards held by departing employees, resulting in $0.1 million, $3.8 million, and $2.2 million of stock-based compensation expense, respectively. During the year ended December 31, 2019, the Company modified the terms of certain equity awards held by non-employees. The modifications resulted in $2.9 million in stock-based compensation expense recorded during the period. For the year ended December 31, 2018 and 2017, there were no modification of options held by non-employees.

Net Income (Loss) Per Share Att

Net Income (Loss) Per Share Attributable to Common Shareholders	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Net Income (Loss) Per Share Attributable to Common Shareholders	10. Net Income (Loss) Per Share Attributable to Common Shareholders 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 income per share is calculated by dividing the net income attributable to common shareholders by the weighted-average number of common share equivalents outstanding for the period, including any dilutive effect from outstanding stock options and warrants using the treasury stock method. The following table sets forth the computation of basic and diluted net income (loss) per share for the periods ended (in thousands, except per share amounts): Year ended December 31, 2019 2018 2017 Basic net income (loss) per common share calculation: Net income (loss) attributable to common shareholders $ 66,858 $ (164,981 ) $ (68,357 ) Net income (loss) attributable to common shareholders - basic $ 66,858 $ (164,981 ) $ (68,357 ) Basic weighted-average common shares outstanding 54,392,304 47,964,368 40,057,365 Basic net income (loss) per common share $ 1.23 $ (3.44 ) $ (1.71 ) Diluted net income (loss) per common share calculation: Net income (loss) attributable to common shareholders $ 66,858 $ (164,981 ) $ (68,357 ) Net income (loss) attributable to common shareholders - diluted $ 66,858 $ (164,981 ) $ (68,357 ) Weighted-average shares used to compute basic net income (loss) per common share 54,392,304 47,964,368 40,057,365 Effect of potentially dilutive securities: Outstanding options 2,406,962 — — Unvested restricted common shares 133,532 — — Weighted-average shares used to compute diluted net income (loss) per common share 56,932,798 47,964,368 40,057,365 Diluted net income (loss) per common share $ 1.17 $ (3.44 ) $ (1.71 ) The Company did not include the securities in the following table in the computation of the net income (loss) per share calculations because the effect would have been anti-dilutive during each period: Year ended December 31, 2019 2018 2017 Outstanding options 3,789,129 6,689,311 6,262,339 Unvested restricted common shares 108,625 327,342 157,515 Total 3,897,754 7,016,653 6,419,854

401 (k) Savings Plan

401 (k) Savings Plan	12 Months Ended
	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
401(k) Savings Plan	11. 401(k) Savings Plan The Company established a defined‑contribution savings plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”) in November 2016. The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis. The Company contributed $1.1 million, $0.6 million and $0.5 million to the 401(k) Plan for the year ended December 31, 2019, 2018 and 2017, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes The Company is subject to U.S. federal and various state corporate income taxes as well as taxes in foreign jurisdictions for the foreign parent and where foreign subsidiaries have been established. Net loss before taxes For the years ended December 31, 2019, 2018 and 2017, the income (loss) before provision for income taxes consist of the following (in thousands): Years Ended December 31, 2019 2018 2017 Domestic $ 9,155 $ 5,966 $ 5,184 Foreign 58,151 (170,394 ) (71,792 ) Total $ 67,306 $ (164,428 ) $ (66,608 ) The (provision for) benefit from income taxes consist of the following (in thousands): Years Ended December 31, 2019 2018 2017 Current income taxes: Federal $ (423 ) $ (416 ) $ (1,533 ) State (59 ) (131 ) (42 ) Foreign — 0 6 Total current income taxes (482 ) (547 ) (1,569 ) Deferred income taxes: Federal 34 (6 ) (477 ) State — — 297 Foreign — — — Total deferred income taxes 34 (6 ) (180 ) Total income tax provision $ (448 ) $ (553 ) $ (1,749 ) A reconciliation of income tax expense computed at the statutory corporate income tax rate to the effective income tax rate for the years ended December 31, 2019, 2018 and 2017 is as follows: Years Ended December 31, 2019 2018 2017 Income tax expense at statutory rate 9.3 % 9.3 % 9.3 % State income tax, net of federal benefit (2.1 )% 0.7 % 0.3 % Nondeductible expenses (0.1 )% 0.0 % 0.0 % Foreign rate differential 2.0 % (0.4 %) (2.5 %) Statutory to US GAAP permanent differences 0.1 % 1.0 % 1.8 % Stock-based compensation (2.0 %) 1.4 % (2.9 %) Impact of deferred rate change (12.2 %) 0.0 % 0.0 % Research credits (5.2 )% 1.8 % 0.8 % Change in valuation allowance 10.9 % (14.1 %) (9.4 %) Effective income tax rate 0.7 % (0.3 %) (2.6 %) The federal statutory rate reflects the Switzerland mixed company service rate. Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets are comprised of the following (in thousands): Years Ended December 31, 2019 2018 Deferred tax assets: Net operating loss carryforwards $ 31,496 $ 25,418 Accruals and reserves 2,868 1,816 Operating lease liabilities 14,214 — Deferred Rent — 3,300 Other deferred tax assets 28 51 Stock-based compensation 5,217 2,871 Deferred revenue (20 ) 3,264 Research credit 7,150 3,322 Total deferred tax assets 60,953 40,042 Less valuation allowance (45,913 ) (36,208 ) Net deferred tax assets 15,040 3,834 Deferred tax liabilities: Depreciation (3,901 ) (3,785 ) Operating lease assets (11,068 ) — Intangible assets (40 ) (49 ) Other deferred tax liabilities (20 ) (22 ) Total deferred tax liabilities (15,029 ) (3,856 ) Long term deferred taxes $ 11 $ (22 ) The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company’s history of worldwide operating losses, the Company has concluded that it is more-likely-than-not that the benefit of its U.S. and non-U.S. deferred tax assets will not be realized. Accordingly, as of December 31, 2019 and 2018, the Company has provided a full valuation allowance against its net deferred tax assets in Switzerland, the United States and the UK for its TRACR subsidiary. The valuation allowance increased by $9.7 million during 2019, which is primarily attributable to increases in the tax rates in Switzerland as a result of tax reform beginning January 1, 2020, partially offset by 2019 taxable income. As of December 31, 2019, the Company had available non-U.S. net operating loss carryforwards of $526.1 million of which $262.3 million relate to Switzerland, $262.3 million relate to the Canton of Zug, and $1.5 million relate to the Company’s wholly-owned subsidiary in the United Kingdom. The net operating losses generated in Switzerland and the Canton of Zug begin to expire in 2022 and the net operating losses generated in the United Kingdom can be carried forward indefinitely. As of December 31, 2019, the Company had U.S. domestic federal research and development credit carryforwards of $4.4 million which expire in 2039 for federal purposes, which are net of uncertain tax positions of $3.0 million. As of December 31, 2019, the Company had U.S. domestic state research and development credit carryforwards of $3.4 million which begin to expire in 2034, which are net of uncertain tax positions of $2.2 million. ASC 740 clarifies the accounting for uncertainty in income taxes recognized in an enterprise’s financial statement by prescribing the minimum recognition threshold and measurement of a tax position taken or expected to be taken in a tax return. As of December 31, 2019, the Company had gross unrecognized tax benefits of $5.2 million of which $4.8 million would favorably impact the effective tax rate if recognized. The Company will recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2019, 2018 and 2017, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s consolidated statements of operations and comprehensive loss. The aggregate changes in gross unrecognized tax benefits was as follows (in thousands): Years Ended December 31, 2019 2018 2017 Balance at beginning of year $ 1,595 $ 354 $ 163 Increases for tax positions taken during current period 2,754 1,212 178 Increases for tax positions taken in prior periods 882 29 13 Decreases for tax positions taken during current period — — — Decreases for tax positions taken in prior periods — — — Balance at end of year $ 5,231 $ 1,595 $ 354 The Company files income tax returns in the U.S. federal jurisdiction, Massachusetts and certain non-U.S. jurisdictions. The Company is subject to U.S. federal, Massachusetts and non-U.S. income tax examinations by authorities for tax years ending after December 31, 2015. Research credits generated in prior tax years that are closed for examination may still be adjusted upon future examination if they have or will be used in a future period. The Company is subject to income tax examinations by authorities in its non-U.S. jurisdictions for all years.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	13. Selected Quarterly Financial Data (Unaudited) The following table sets forth the Company’s quarterly financial data for the two years ended December 31, 2019. 2019 First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue $ 328 $ 318 $ 211,928 $ 77,016 Total operating expenses 48,751 55,301 72,765 $ 66,033 (Loss) income from operations (48,423 ) (54,983 ) 139,163 $ 10,983 Net (loss) income (48,408 ) (53,699 ) 138,423 $ 30,542 Net (loss) income per share attributable to common shareholders: Basic $ (0.93 ) $ (1.01 ) 2.52 $ 0.53 Diluted $ (0.93 ) $ (1.01 ) $ 2.40 $ 0.51 Weighted-average common shares outstanding used in net (loss) income per share attributable to common shareholders: Basic 52,093,208 53,188,041 54,829,057 57,395,839 Diluted 52,093,208 53,188,041 57,598,901 60,233,927 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue $ 1,358 $ 1,088 $ 563 $ 115 Total operating expenses 28,355 38,374 49,995 $ 45,343 Loss from operations (26,997 ) (37,286 ) (49,432 ) $ (45,228 ) Net loss (28,300 ) (38,380 ) (50,711 ) $ (47,590 ) Net loss per share attributable to common shareholders: Basic $ (0.62 ) $ (0.82 ) $ (1.07 ) $ (0.92 ) Diluted $ (0.62 ) $ (0.82 ) $ (1.07 ) $ (0.92 ) Weighted-average common shares outstanding used in net loss per share attributable to common shareholders: Basic 45,877,428 46,842,316 47,391,988 51,688,383 Diluted 45,877,428 46,842,316 47,391,988 51,688,383

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	14. Related Party Transactions Casebia Prior to the termination of the joint venture, Casebia was a related party under ASC 850, Related Party Disclosures . Joint Venture with Bayer Healthcare LLC. Vertex In the fourth quarter of 2018, upon becoming owners of record of more than 10% of the voting interest of the Company, Vertex became a related party under ASC 850 . Agreements with Vertex Pharmaceuticals Incorporated and certain of its subsidiaries

Summary of Significant Accoun_2

Summary of Significant Accounting Policies and Basis of Presentation (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly-owned subsidiaries as of December 31, 2019. All intercompany accounts and transactions have been eliminated. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board. Prior to December 13, 2019, the Company accounted for its 50% investment in Casebia Therapeutics, Limited Liability Partnership (“Casebia”) under the equity method. As described in Note 7, on December 13, 2019, Casebia became a fully-owned subsidiary and, as a result, the Company consolidated Casebia’s financial results from that date forward. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, revenue recognition, equity-based compensation expense and reported amounts of expenses during the period. Significant estimates in these consolidated financial statements have been made in connection with revenue recognition and equity-based compensation expense. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Certain items in the prior year’s condensed consolidated financial statements have been reclassified to conform to the current presentation. As a result, no subtotals in the prior year condensed consolidated financial statements were impacted.
Segment Information	Segment Information The Company and the Company’s chief operating decision maker, namely, the chief executive officer, view the Company’s operations and manage its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology.
Foreign Currency Translation and Transactions	Foreign Currency Translation and Transactions The majority of the Company’s operations occur in entities that have the U.S. dollar as their functional currency. Non-U.S. dollar denominated functional currency subsidiaries have assets and liabilities translated into U.S. dollars at rates of exchange in effect at the end of the year. Revenue and expense amounts are translated using the average exchange rates for the period. Net unrealized gains and losses resulting from foreign currency translation are included in “Accumulated other comprehensive income (loss).” Net foreign currency exchange transaction gains or losses are included in “Other income (expense), net” on the Company’s consolidated statement of operations, the impact of which is not significant.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with maturities of three months or less from the purchase date to be cash equivalents. As of December 31, 2019 and 2018, the Company had $943.8 million and $456.6 million in cash equivalents, respectively.
Restricted Cash	Restricted Cash As of December 31, 2019 and 2018, the Company had $5.0 million and $3.2 million, respectively, in restricted cash representing letters of credit securing the Company’s obligations under certain leased facilities in Cambridge, Massachusetts, as well as certain credit card arrangements. The letters of credit are secured by cash held in a restricted depository account.
Other Receivables	Other Receivables Other receivables of $4.1 million and $3.4 million at December 31, 2019 and 2018, respectively, consists of receivables from Vertex and are included with prepaid and other current assets in the consolidated balance sheet. These amounts represent the balance due from the portion of our arrangement accounted for under ASC 808, Collaborative Arrangements
Concentrations of Credit Risk and Off-balance Sheet Risk	Concentrations of Credit Risk and Off-balance Sheet Risk Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash. The Company’s cash is held in accounts with financial institutions that management believes are creditworthy. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no financial instruments with off-balance sheet risk of loss.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company has certain financial assets and liabilities recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements: Level 1 — Quoted prices in active markets that are accessible at the market date for identical unrestricted assets or liabilities. Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs for which all significant inputs are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying amount of accounts receivable, other receivables, accounts payable and accrued expenses as reported on the consolidated balance sheets as of December 31, 2019 and 2018, approximate fair value, due to the short-term duration of these instruments.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Asset Estimated useful life Computer equipment 3 years Furniture, fixtures and other 5 years Laboratory equipment 5 years Leasehold improvements Shorter of useful life or remaining lease term
Impairment of Long-lived Assets	Impairment of Long-lived Assets The Company reviews long-lived assets when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparison of the book values of the assets to future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets.
Revenue Recognition	Revenue Recognition Effective January 1, 2018, the Company adopted ASC Topic 606, Revenue from Contracts with Customers by recognizing the cumulative effect of initially applying ASC 606 as an adjustment to the opening balance of equity at January 1, 2018. The reported results for 2019 and 2018 reflect the application of ASC 606 guidance while the reported results for 2017 were prepared under the guidance of ASC 605, Revenue Recognition (“ASC 605”). In connection with adopting ASC 606, t he Company elected a practical expedient and applied ASC 606 only to contracts that were not completed at the date of initial application. In addition, the Company applied the practical expedient in ASC 606-10-65-1 in identifying the satisfied and unsatisfied performance obligations, determining the transaction price and allocating the transaction price under the practical expedient in ASC 606 ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases and collaboration arrangements. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: 1) Identify the contract with the customer A contract with a customer exists when (i) the Company enters into an enforceable contract with a customer that defines each party’s rights regarding the goods or services to be transferred and identifies the related payment terms, (ii) the contract has commercial substance and (iii) the Company determines that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration. 2) Identify the performance obligations in the contract Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct, whereby the customer can benefit from the good or service either on its own or together with other available resources, and are distinct in the context of the contract, whereby the transfer of the good or service is separately identifiable from other promises in the contract. To the extent a contract includes multiple promised goods and services, the Company must apply judgment to determine whether promised goods and services are capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation. 3) Determine the transaction price The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration such as research, development, regulatory and commercial milestones, the Company determines if it is probable that it will receive such amounts and there is no risk of a significant revenue reversal. When the Company cannot conclude that receipt of such amounts is probable, the Company constrains the related variable consideration resulting in its exclusion from transaction consideration. In determining the portion of the transaction consideration to be constrained, the Company considers the probability and uncertainty that the related research, developmental, regulatory and commercial milestones will be achieved given the nature of research and clinical development and the stage of the underlying programs. This assessment is performed at each reporting period. In making this evaluation, the Company considers both internal and external information available, including information from industry publications and other relevant factors. Changes to the constraint of variable consideration can have a material effect on the amount of revenue recognized in the period. 4) Allocate the transaction consideration to performance obligations in the contract If the contract contains a single performance obligation, the entire transaction consideration is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction consideration to each performance obligation on a relative standalone selling price basis unless the transaction consideration is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices. In determining these estimated standalone selling prices, the Company makes a number of significant judgements including, for licenses, management’s assumptions regarding probability weighted projected discounted cash flows for each of the collaboration development programs. The estimated standalone selling prices are sensitive to changes in assumptions, such as probabilities of scientific success, discount rate and certain assumptions that form the basis of forecasted cash flows. In developing these assumptions, management considers both internal and external available, . Changes to these assumptions can have a material effect on the allocation of the transaction consideration to performance obligations, as well as the amount and timing of revenue recognized. 5) Recognize revenue when or as the Company satisfies a performance obligation The Company satisfies performance obligations over time or at a point in time, depending on the nature of the performance obligation. Revenue is recognized over time if the customer simultaneously receives and consumes the benefits provided by the entity’s performance, the entity’s performance creates or enhances an asset that the customer controls as the asset is created or enhanced, or the entity’s performance does not create an asset with an alternative use to the entity and the entity has an enforceable right to payment for performance completed to date. If the entity does not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring the control of a promised good or service to a customer. Contract Balances The Company recognizes a contract asset when the Company transfers goods or services to a customer before the customer pays consideration or before payment is due, excluding any amounts presented as a receivable (i.e. accounts receivable). A contract asset is an entity’s right to consideration in exchange for goods or services that the entity has transferred to a customer. The contract liabilities (i.e. deferred revenue) primarily relate to contracts where we have received payment, but we have not yet satisfied the related performance obligations. The Company recorded contract assets of $25.7 million and $0.0 million as of December 31, 2019 and 2018, respectively. Deferred revenue as of December 31, 2019 and 2018 was $12.7 million and $57.8 million. The change in contract assets and deferred revenue is related to the collaboration agreement with Vertex described in Note 7.
Collaboration Arrangements	Collaboration Arrangements The Company records the elements of its collaboration agreements that represent joint operating activities in accordance with ASC 808, Collaborative arrangements The Company evaluates the proper presentation of the commercial activities and the profit and loss sharing associated with the collaboration agreements. ASC 808 states that when payments between parties in a collaborative arrangement are not within the scope of other authoritative accounting literature, the income statement classification should be based on the nature of the arrangement, the nature of its business operations and the contractual terms of the arrangement. To the extent that these payments are not within the scope of other authoritative accounting literature, the income statement classification for the payments shall be based on an analogy to authoritative accounting literature or if there is no appropriate analogy, a reasonable, rational and consistently applied accounting policy election.
Research and Development Expenses	Research and Development Expenses Research and development costs are charged to expense as costs are incurred in performing research and development activities, including salaries and benefits, facilities costs, overhead costs, clinical study and related clinical manufacturing costs, license and milestone fees, contract services and other related costs. Research and development costs, including up-front fees and milestones paid to collaborators, are also expensed as incurred. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense. The Company accrues costs for clinical trial activities based upon estimates of the services received and related expenses incurred that have yet to be invoiced by the contract research organizations, clinical study sites, laboratories, consultants or other clinical trial vendors that perform the activities. The Company recognizes the reimbursement associated with collaborative activities to its collaborative partners as research and development expense in the period the services are provided.
Leases	Leases Effective January 1, 2019, the Company adopted ASC 842, Leases Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and short-term and long-term lease liabilities, as applicable. The Company does not have financing leases. Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. Prospectively, the Company will adjust the right-of-use assets for straight-line rent expense or any incentives received and remeasure the lease liability at the net present value using the same incremental borrowing rate that was in effect as of the lease commencement or transition date. The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. Assumptions made by the Company at the commencement date are re-evaluated upon occurrence of certain events, including a lease modification. A lease modification results in a separate contract when the modification grants the lessee an additional right of use not included in the original lease and when lease payments increase commensurate with the standalone price for the additional right of use. When a lease modification results in a separate contract, it is accounted for in the same manner as a new lease.
Equity-Based Compensation Expense	Equity Based Compensation Expense The Company’s share-based compensation programs grant awards that have included stock options, restricted stock units and restricted stock awards. Grants are awarded to employees and non-employees, including directors. The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments to employees and non-employee directors, including grants of employee stock options and restricted stock units and modifications to existing stock options, to be recognized in the consolidated statements of operations and comprehensive income (loss) based on their fair values. The Company uses the Black-Scholes option pricing model to determine the fair value of options granted. The Company accounts for forfeitures as they occur instead of estimating forfeitures at the time of grant and revising those estimates in subsequent periods if actual forfeitures differ from its estimates. Stock-based compensation expense recognized in the financial statements is based on awards for which performance or service conditions are expected to be satisfied. Prior to the adoption of ASU No. 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting The Company’s stock-based awards are subject to service or performance-based vesting conditions. Compensation expense related to awards to employees, directors and non-employees with service-based vesting conditions is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term. Compensation expense related to awards to employees and non-employees with performance-based vesting conditions is recognized based on the grant date fair value over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable. The Company expenses restricted stock unit awards to employees based on the fair value of the award on a straight-line basis over the associated service period of the award. The Company estimates the fair value of its option awards to employees, directors and non-employees using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including (i) the expected stock price volatility, (ii) the calculation of expected term of the award, (iii) the risk-free interest rate and (iv) expected dividends. Due to the lack of complete company-specific historical and implied volatility data for the full expected term of the stock-based awards, the Company bases its estimate of expected volatility on a representative group of publicly traded companies in addition to its own volatility data. For these analyses, the Company selected companies with comparable characteristics to its own, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected life of the stock-based awards. The Company computes historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. The Company has estimated the expected term of its employee stock options using the “simplified” method, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option, due to its lack of sufficient historical data. The risk-free interest rates for periods within the expected term of the option are based on the U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid, and does not expect to pay, dividends in the foreseeable future.
Patent Costs	Patent Costs Costs to secure and prosecute patent applications and other legal costs related to the protection of the Company’s intellectual property are expensed as incurred and are classified as general and administrative expenses in the Company’s consolidated statements of operations.
Income Taxes	Income Taxes Income taxes are recorded in accordance with ASC Topic 740, Income Taxes The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2019, and 2018, the Company does not have any significant uncertain tax positions. The Company’s practice is to recognize interest and/or penalties related to income tax matters in income tax expense. See Note 12 for further details.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) consists of net income or loss and other comprehensive income (loss). Other comprehensive income (loss) consists of foreign currency translation adjustments.
Variable Interest Entities	Variable Interest Entities The Company reviews each legal entity formed by parties related to the Company to determine whether or not the Company has a variable interest in the entity and whether or not the entity would meet the definition of a variable interest entity (“VIE”) in accordance with ASC Topic 810, Consolidation If the Company determines it is the primary beneficiary of a VIE that meets the definition of a business, the Company measures the assets, liabilities and noncontrolling interests of the newly consolidated entity at fair value in accordance with ASC Topic 805, Business Combinations In February 2016, Casebia, was formed in the United Kingdom. In March 2016, upon consummation of the joint venture (“JV”), Bayer Healthcare LLC and certain of its affiliates (“Bayer”) and the Company each received a 50% equity interest in the entity in exchange for their contributions to the entity. The Company determined that Casebia was considered a VIE and concluded that it is not the primary beneficiary of the VIE. As such, the Company has not historically consolidated Casebia’s results into the consolidated financial statements. As described in Note 7, on December 13, 2019, Casebia became a fully-owned subsidiary and, as a result, the Company consolidated Casebia’s financial results accordingly from that point forward.
Net Income (Loss) Per Share Attributable to Common Shareholders	Net Income (Loss) Per Share Attributable to Common Shareholders Basic net income (loss) per share is calculated by dividing net income (loss) attributable to common shareholders by the weighted-average number of common shares outstanding during the period. Diluted net income per share is calculated by dividing the net income attributable to common shareholders by the weighted-average number of common equivalent shares outstanding for the period, including any dilutive effect from outstanding stock options and restricted stock units using the treasury stock method. See Note 10 for further details.
New Accounting Pronouncements - Recently Adopted	New Accounting Pronouncements – Recently Adopted Leases As discussed above, the Company adopted ASC 842, using the required modified retrospective approach, effective January 1, 2019. The Company chose to apply the transition provisions as of the period of adoption. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which, among other things, allowed the Company to carry forward the historical lease classification. In addition, the Company elected the practical expedient not to apply the recognition requirements in the lease standard to short-term leases (a lease that at commencement date has a lease term of 12 months or less and does not contain a purchase option that it is reasonably certain to exercise) and the practical expedient that permits lessees to make an accounting policy election (by class of underlying asset) to account for each separate lease component of a contract and its associated non-lease components as a single lease component. The adoption of the new standard resulted in the recording net lease assets and lease liabilities of $26.1 million and $37.6 million, respectively, as of January 1, 2019. The difference between the additional lease assets and lease liabilities is primarily due to the change in classification of lease incentives from liabilities to a reduction in our net lease assets. The standard had no impact on our net loss or cash flows. Impact of Adopting ASC 842 on the Financial Statements January 1, 2019 Prior to ASC 842 Adoption ASC 842 Adjustment January 1, 2019 As Adjusted Consolidated Balance Sheet Data (in thousands): Prepaid expenses and other current assets (1) $ 9,658 $ (553 ) $ 9,105 Operating lease assets (2) $ — $ 26,087 $ 26,087 Deferred rent (3)(4) $ 1,026 $ (1,026 ) $ — Deferred rent non-current (3) $ 11,052 $ (11,052 ) $ — Operating lease liabilities (5) $ — $ 4,930 $ 4,930 Non-current operating lease liabilities (5) $ — $ 32,682 $ 32,682 (1) Represents reclassification of prepaid rent to operating lease assets. (2) Represents capitalization of operating lease assets and reclassification of equipment licenses from prepaid expenses to operating lease assets, offset by reclassification of deferred rent to operating lease assets. (3) Represents reclassification of deferred rent and tenant incentives to operating lease assets. (4) As of December 31, 2018, the deferred rent balance was $1,202, which included $176 of sublease income received prior to year-end but not due until January 1, 2019. (5) Represents recognition of operating lease liabilities.
New Accounting Pronouncements – Not Yet Adopted	New Accounting Pronouncements – Not Yet Adopted Credit Losses In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 362): Measurement of Credit Losses on Financial Statements , Financial Instruments-Overall

Summary of Significant Accoun_3

Summary of Significant Accounting Policies and Basis of Presentation (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule of Estimated Useful Lives of Assets	Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Asset Estimated useful life Computer equipment 3 years Furniture, fixtures and other 5 years Laboratory equipment 5 years Leasehold improvements Shorter of useful life or remaining lease term
ASC 842 [Member]
Impact of Adoption ASC 842 on the Financial Statements	Impact of Adopting ASC 842 on the Financial Statements January 1, 2019 Prior to ASC 842 Adoption ASC 842 Adjustment January 1, 2019 As Adjusted Consolidated Balance Sheet Data (in thousands): Prepaid expenses and other current assets (1) $ 9,658 $ (553 ) $ 9,105 Operating lease assets (2) $ — $ 26,087 $ 26,087 Deferred rent (3)(4) $ 1,026 $ (1,026 ) $ — Deferred rent non-current (3) $ 11,052 $ (11,052 ) $ — Operating lease liabilities (5) $ — $ 4,930 $ 4,930 Non-current operating lease liabilities (5) $ — $ 32,682 $ 32,682 (1) Represents reclassification of prepaid rent to operating lease assets. (2) Represents capitalization of operating lease assets and reclassification of equipment licenses from prepaid expenses to operating lease assets, offset by reclassification of deferred rent to operating lease assets. (3) Represents reclassification of deferred rent and tenant incentives to operating lease assets. (4) As of December 31, 2018, the deferred rent balance was $1,202, which included $176 of sublease income received prior to year-end but not due until January 1, 2019. (5) Represents recognition of operating lease liabilities.

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net, consists of the following (in thousands): As of December 31, 2019 2018 Computer equipment $ 727 $ 443 Furniture, fixtures, and other 3,215 2,453 Laboratory equipment 16,640 8,964 Leasehold improvements 21,400 13,776 Construction work in process 1,394 239 Total property and equipment, gross 43,376 25,875 Accumulated Depreciation (12,046 ) (7,375 ) Total property and equipment, net $ 31,330 $ 18,500

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2019
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): As of December 31, 2019 2018 Payroll and employee-related costs $ 15,229 $ 7,321 Research costs 9,434 7,973 Licensing fees 750 625 Professional fees 2,040 1,848 Intellectual property costs 2,311 2,193 Accrued property and equipment 407 294 Other 9 598 Total $ 30,180 $ 20,852

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Summary of Lease Assets and Liabilities	The following table summarizes the lease assets and liabilities as of December 31, 2019 (in thousands): As of December 31, 2019 Assets Operating lease assets $ 41,502 Total lease assets 41,502 Liabilities Current Operating lease liabilities 8,489 Non-current Operating lease liabilities, net of current portion 44,050 Total lease liabilities $ 52,539
Summary of Operating Lease Costs Included in Research and Development and General and Administrative Expense, as well as Sublease Income	The following table summarizes operating lease costs included in research and development and general and administrative expense, as well as sublease income for the twelve months ended December 31, 2019 (in thousands): Twelve Months Ended December 31, 2019 Operating lease costs $ 8,067 Short-term lease costs 4,554 Variable lease costs 4,282 Sublease income (525 ) Net lease cost $ 16,378
Summary of Maturity of Undiscounted Payments Due under Lease Liabilities and Present Value of Those Liabilities	The following table summarizes the maturity of undiscounted payments due under lease liabilities and the present value of those liabilities as of December 31, 2019 (in thousands): Total 2020 $ 13,963 2021 11,824 2022 10,167 2023 10,269 2024 8,308 Thereafter 15,678 Total $ 70,209 Present value adjustment (17,670 ) Present value of lease liabilities $ 52,539
Summary of Lease Term and Discount Rate	The following table summarizes the lease term and discount rate as of December 31, 2019 : As of December 31, 2019 Weighted-average remaining lease term (years) Operating leases 6.0 Weighted-average discount rate Operating leases 9.9 %
Lessee, Operating Lease Cash Flow Payments	The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the twelve months ended December 31, 2019 (in thousands): Twelve Months Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities $ 8,420 Operating cash flows from operating leases $ 8,420

Significant Contracts (Tables)

Significant Contracts (Tables)	12 Months Ended
	Dec. 31, 2019
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 VIE, 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)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Schedule of Share Capital	Share Capital consisted of the following (in thousands): As of December 31, Type of Share Capital Conditional Capital 2019 2018 Common shares Registered share capital 61,037 52,268 Common shares Authorized share capital 19,246 17,577 Common shares Conditional share capital - Bonds or similar debt instruments 4,920 4,920 Common shares Conditional share capital - Employee benefit plans 18,698 15,579 Total 103,901 90,344

Equity-based Compensation (Tabl

Equity-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock-Based Compensation Expense	Stock‑based compensation expense by classification within the consolidated statements of operations and comprehensive income (loss) is as follows (in thousands): Years Ended December 31, 2019 2018 2017 Research and development $ 23,273 $ 17,557 $ 8,800 General and administrative 20,784 17,428 10,073 Loss from equity method investment 5,467 4,275 1,763 Total $ 49,524 $ 39,260 $ 20,636
Fair Value of Each Option Issued to Employees and Non-employees Estimated Using Black-Scholes Option-Pricing Model	The fair value of each option issued to employees and non-employees was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions: Years Ended December 31, 2019 2018 2017 Options granted 2,832,784 2,209,597 2,999,847 Weighted-average exercise price $ 39.16 $ 51.73 $ 16.98 Weighted-average grant date fair value $ 24.57 $ 33.82 $ 11.16 Assumptions: Expected volatility 68.9 % 71.9 % 72.5 % Expected term (in years) 6.0 6.0 6.1 Risk-free interest rate 2.2 % 2.8 % 2.0 % Expected dividend yield 0.0 % 0.0 % 0.0 %
Summary of Stock Option Activity	The following table summarizes stock option activity under the Company’s equity award plans (intrinsic value in thousands): Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding at December 31, 2018 6,689,311 $ 25.42 8.3 $ 68,572 Granted 2,832,784 $ 39.16 Exercised (1,180,644 ) $ 14.91 Cancelled or forfeited (559,014 ) $ 35.35 Outstanding at December 31, 2019 7,782,437 $ 31.30 8.2 231,554 Exercisable at December 31, 2019 3,328,398 $ 24.07 7.4 $ 122,774 Vested and expected to vest at December 31, 2019 7,782,437 $ 31.30 8.2 $ 231,554
Summary of Restricted Stock Activity	The following table summarizes the restricted stock activity under the Company’s equity award plans (shares in thousands): Shares Weighted- Average Grant Date Fair Value Unvested restricted common shares at December 31, 2018 327,342 $ 36.72 Granted 503,600 62.11 Vested (86,758 ) 20.38 Cancelled or forfeited (44,650 ) 44.50 Unvested restricted common shares at December 31, 2019 699,534 $ 56.53

Net Income (Loss) Per Share A_2

Net Income (Loss) Per Share Attributable to Common Shareholders (Tables)	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Net Income (Loss) per Share	The following table sets forth the computation of basic and diluted net income (loss) per share for the periods ended (in thousands, except per share amounts): Year ended December 31, 2019 2018 2017 Basic net income (loss) per common share calculation: Net income (loss) attributable to common shareholders $ 66,858 $ (164,981 ) $ (68,357 ) Net income (loss) attributable to common shareholders - basic $ 66,858 $ (164,981 ) $ (68,357 ) Basic weighted-average common shares outstanding 54,392,304 47,964,368 40,057,365 Basic net income (loss) per common share $ 1.23 $ (3.44 ) $ (1.71 ) Diluted net income (loss) per common share calculation: Net income (loss) attributable to common shareholders $ 66,858 $ (164,981 ) $ (68,357 ) Net income (loss) attributable to common shareholders - diluted $ 66,858 $ (164,981 ) $ (68,357 ) Weighted-average shares used to compute basic net income (loss) per common share 54,392,304 47,964,368 40,057,365 Effect of potentially dilutive securities: Outstanding options 2,406,962 — — Unvested restricted common shares 133,532 — — Weighted-average shares used to compute diluted net income (loss) per common share 56,932,798 47,964,368 40,057,365 Diluted net income (loss) per common share $ 1.17 $ (3.44 ) $ (1.71 )
Schedule of Antidilutive Securities not Include in Computation of Net Income (Loss) per Share	The Company did not include the securities in the following table in the computation of the net income (loss) per share calculations because the effect would have been anti-dilutive during each period: Year ended December 31, 2019 2018 2017 Outstanding options 3,789,129 6,689,311 6,262,339 Unvested restricted common shares 108,625 327,342 157,515 Total 3,897,754 7,016,653 6,419,854

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Schedule of Income (Loss) Before Provision for Income Taxes	For the years ended December 31, 2019, 2018 and 2017, the income (loss) before provision for income taxes consist of the following (in thousands): Years Ended December 31, 2019 2018 2017 Domestic $ 9,155 $ 5,966 $ 5,184 Foreign 58,151 (170,394 ) (71,792 ) Total $ 67,306 $ (164,428 ) $ (66,608 )
Schedule of (Provision for) Benefit from Income Taxes	The (provision for) benefit from income taxes consist of the following (in thousands): Years Ended December 31, 2019 2018 2017 Current income taxes: Federal $ (423 ) $ (416 ) $ (1,533 ) State (59 ) (131 ) (42 ) Foreign — 0 6 Total current income taxes (482 ) (547 ) (1,569 ) Deferred income taxes: Federal 34 (6 ) (477 ) State — — 297 Foreign — — — Total deferred income taxes 34 (6 ) (180 ) Total income tax provision $ (448 ) $ (553 ) $ (1,749 )
Schedule of Reconciliation of Income Tax Expense Computed at Statutory Corporate Income Tax Rate to Effective Income Tax Rate	A reconciliation of income tax expense computed at the statutory corporate income tax rate to the effective income tax rate for the years ended December 31, 2019, 2018 and 2017 is as follows: Years Ended December 31, 2019 2018 2017 Income tax expense at statutory rate 9.3 % 9.3 % 9.3 % State income tax, net of federal benefit (2.1 )% 0.7 % 0.3 % Nondeductible expenses (0.1 )% 0.0 % 0.0 % Foreign rate differential 2.0 % (0.4 %) (2.5 %) Statutory to US GAAP permanent differences 0.1 % 1.0 % 1.8 % Stock-based compensation (2.0 %) 1.4 % (2.9 %) Impact of deferred rate change (12.2 %) 0.0 % 0.0 % Research credits (5.2 )% 1.8 % 0.8 % Change in valuation allowance 10.9 % (14.1 %) (9.4 %) Effective income tax rate 0.7 % (0.3 %) (2.6 %)
Schedule of Significant Components of Company's Deferred Tax Assets	Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets are comprised of the following (in thousands): Years Ended December 31, 2019 2018 Deferred tax assets: Net operating loss carryforwards $ 31,496 $ 25,418 Accruals and reserves 2,868 1,816 Operating lease liabilities 14,214 — Deferred Rent — 3,300 Other deferred tax assets 28 51 Stock-based compensation 5,217 2,871 Deferred revenue (20 ) 3,264 Research credit 7,150 3,322 Total deferred tax assets 60,953 40,042 Less valuation allowance (45,913 ) (36,208 ) Net deferred tax assets 15,040 3,834 Deferred tax liabilities: Depreciation (3,901 ) (3,785 ) Operating lease assets (11,068 ) — Intangible assets (40 ) (49 ) Other deferred tax liabilities (20 ) (22 ) Total deferred tax liabilities (15,029 ) (3,856 ) Long term deferred taxes $ 11 $ (22 )
Schedule of Aggregate Changes in Gross Unrecognized Tax Benefits	The aggregate changes in gross unrecognized tax benefits was as follows (in thousands): Years Ended December 31, 2019 2018 2017 Balance at beginning of year $ 1,595 $ 354 $ 163 Increases for tax positions taken during current period 2,754 1,212 178 Increases for tax positions taken in prior periods 882 29 13 Decreases for tax positions taken during current period — — — Decreases for tax positions taken in prior periods — — — Balance at end of year $ 5,231 $ 1,595 $ 354

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data	The following table sets forth the Company’s quarterly financial data for the two years ended December 31, 2019. 2019 First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue $ 328 $ 318 $ 211,928 $ 77,016 Total operating expenses 48,751 55,301 72,765 $ 66,033 (Loss) income from operations (48,423 ) (54,983 ) 139,163 $ 10,983 Net (loss) income (48,408 ) (53,699 ) 138,423 $ 30,542 Net (loss) income per share attributable to common shareholders: Basic $ (0.93 ) $ (1.01 ) 2.52 $ 0.53 Diluted $ (0.93 ) $ (1.01 ) $ 2.40 $ 0.51 Weighted-average common shares outstanding used in net (loss) income per share attributable to common shareholders: Basic 52,093,208 53,188,041 54,829,057 57,395,839 Diluted 52,093,208 53,188,041 57,598,901 60,233,927 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue $ 1,358 $ 1,088 $ 563 $ 115 Total operating expenses 28,355 38,374 49,995 $ 45,343 Loss from operations (26,997 ) (37,286 ) (49,432 ) $ (45,228 ) Net loss (28,300 ) (38,380 ) (50,711 ) $ (47,590 ) Net loss per share attributable to common shareholders: Basic $ (0.62 ) $ (0.82 ) $ (1.07 ) $ (0.92 ) Diluted $ (0.62 ) $ (0.82 ) $ (1.07 ) $ (0.92 ) Weighted-average common shares outstanding used in net loss per share attributable to common shareholders: Basic 45,877,428 46,842,316 47,391,988 51,688,383 Diluted 45,877,428 46,842,316 47,391,988 51,688,383

Organization and Operations - A

Organization and Operations - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Company incorporation date									Oct. 31, 2013
Accumulated deficit	$ (224,711)				$ (291,569)				$ (224,711)	$ (291,569)
Cash and cash equivalents	943,771				456,649				943,771	456,649	$ 239,758
Net income	$ 30,542	$ 138,423	$ (53,699)	$ (48,408)	$ (47,590)	$ (50,711)	$ (38,380)	$ (28,300)	$ 66,858	$ (164,981)	$ (68,357)

Summary of Significant Accoun_4

Summary of Significant Accounting Policies and Basis of Presentation - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019USD ($)Segment	Dec. 12, 2019	Jan. 01, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Mar. 31, 2016	Feb. 12, 2016
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Cash and cash equivalents	$ 943,771,000			$ 456,649,000	$ 239,758,000
Restricted Cash	5,041,000			3,163,000	3,154,000
Significant uncertain tax positions	0			0	$ 0
Net lease assets	41,502,000
Net lease liabilities	52,539,000
ASC 842 [Member]
Summary Of Significant Accounting Policies [Line Items]
Net lease assets			$ 26,087,000
Net lease liabilities			$ 37,600,000
Vertex and Casebia [Member] | Collaborative Arrangement [Member]
Summary Of Significant Accounting Policies [Line Items]
Other receivables	$ 4,100,000			$ 3,400,000
Casebia Therapeutics Limited Liability Partnership [Member]
Summary Of Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage		50.00%				50.00%	50.00%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies and Basis of Presentation - Schedule of Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 2019
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	3 years
Furniture, Fixtures, and Other [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	5 years
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	5 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Leasehold improvements	Shorter of useful life or remaining lease term

Summary of Significant Accoun_6

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

Summary of Significant Accoun_7

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

Property and Equipment, net - S

Property and Equipment, net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 43,376	$ 25,875
Accumulated Depreciation	(12,046)	(7,375)
Total property and equipment, net	31,330	18,500
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	727	443
Furniture, Fixtures, and Other [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	3,215	2,453
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	16,640	8,964
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	21,400	13,776
Construction Work in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 1,394	$ 239

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 4.7	$ 3.5	$ 3

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued Liabilities Current [Abstract]
Payroll and employee-related costs	$ 15,229	$ 7,321
Research costs	9,434	7,973
Licensing fees	750	625
Professional fees	2,040	1,848
Intellectual property costs	2,311	2,193
Accrued property and equipment	407	294
Other	9	598
Total	$ 30,180	$ 20,852

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended				12 Months Ended
	Nov. 30, 2019	May 31, 2019	May 31, 2016	Jun. 30, 2015	Dec. 31, 2019
2015 Lease [Member]
Lessee Lease Description [Line Items]
Lease commencement date				Nov. 15, 2015
Lease expiration date				Feb. 28, 2022
2016 Sublease [Member]
Lessee Lease Description [Line Items]
Lease commencement date			Dec. 23, 2016
Lease expiration date			Dec. 31, 2026
Lessee, operating sublease, option to extend					an option to extend the term of the sublease for an additional five-year period if, at the time of expiration of the initial term
Lessee, operating sublease, existence of option to extend			true
Extended term of lease expiration			5 years
2019 Lease [Member]
Lessee Lease Description [Line Items]
Lease commencement date		Jun. 1, 2019
Lease expiration date		Nov. 30, 2026
Extended term of lease expiration		5 years
Lessee, operating lease, option to extend					an option to extend the term of the lease for an additional five-year period based on certain conditions within the Company’s control.
Lessee, operating lease, existence of option to extend		true
2019 Sublease [Member]
Lessee Lease Description [Line Items]
Lease expiration date					Mar. 31, 2024
Lessee, operating sublease, option to extend					an option to extend the term of the sublease for an additional five-year period if, at the time of expiration of the initial term
Lessee, operating sublease, existence of option to extend					true
Extended term of lease expiration					5 years
Lease Arrangement [Member]
Lessee Lease Description [Line Items]
Upfront payment	$ 2.6
Annual rental payments	$ 3.7
Rental payments period	5 years

Leases - Summary of Lease Asset

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

Leases - Summary of Operating L

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

Leases - Summary of Maturity of

Leases - Summary of Maturity of Undiscounted Payments Due under Lease Liabilities and Present Value of Those Liabilities (Detail) $ in Thousands	Dec. 31, 2019USD ($)
Leases [Abstract]
2020	$ 13,963
2021	11,824
2022	10,167
2023	10,269
2024	8,308
Thereafter	15,678
Total	70,209
Present value adjustment	(17,670)
Present value of lease liabilities	$ 52,539

Leases - Summary of Lease Term

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

Leases - Summary of Cash Paid f

Leases - Summary of Cash Paid for Amounts Included in Measurement of Lease Liabilities (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 8,420
Operating cash flows from operating leases	$ 8,420

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)Claim	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Contingencies And Commitments [Line Items]
Cost sharing expensed relating to patent maintenance, defense and prosecution, incurred	$ 2.9	$ 2.4	$ 1.2
Cost sharing expensed relating to patent maintenance, defense and prosecution, accrued	$ 1.5	$ 1.9
Patent Applications Co-owned by CVC Group [Member]
Contingencies And Commitments [Line Items]
Number of patent and patent applications pending | Claim	14
Patents and Patent Application Owned by Broad [Member]
Contingencies And Commitments [Line Items]
Number of patent and patent applications pending | Claim	13
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 ($)Product	Dec. 18, 2018USD ($)	Nov. 15, 2018USD ($)shares	Sep. 24, 2018USD ($)shares	Sep. 17, 2018USD ($)Installment	Oct. 26, 2015USD ($)	Oct. 31, 2019License	Dec. 18, 2018USD ($)	Nov. 14, 2018USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)Option		Dec. 31, 2018USD ($)		Dec. 31, 2017USD ($)		Dec. 12, 2019	Mar. 31, 2016	Feb. 12, 2016
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Non-current deferred revenue											$ 11,776,000				$ 57,780,000				$ 11,776,000		$ 57,780,000
Collaboration revenue											77,016,000	$ 211,928,000	$ 318,000	$ 328,000	115,000	$ 563,000	$ 1,088,000	$ 1,358,000	289,590,000	[1]	3,124,000	[1]	$ 40,997,000	[1]
Current deferred revenue											960,000				102,000				960,000		102,000
Research and development expense	[2]																		$ 179,362,000		113,773,000		69,800,000
Date of joint venture agreement																			Dec. 19, 2015
Operating expenses											66,033,000	$ 72,765,000	$ 55,301,000	$ 48,751,000	45,343,000	$ 49,995,000	$ 38,374,000	$ 28,355,000	$ 242,850,000		162,067,000		105,645,000
Stock-based compensation expense																			49,524,000		39,260,000		20,636,000
Issuance of common shares, value																			414,789,000		307,053,000
Net proceeds from issuance of common shares																			415,019,000		307,053,000
Other (expense) income																			26,033,000		(1,210,000)		(197,000)
Casebia Therapeutics Limited Liability Partnership [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense																			700,000		3,800,000		4,500,000
Reimbursements from research and license agreements																			$ 200,000		900,000		4,400,000
Date of formation of joint venture entity																			Feb. 12, 2016
Equity method investment, ownership percentage																									50.00%	50.00%	50.00%
Stock-based compensation expense																			$ 5,500,000		4,300,000		1,800,000
Unrecognized equity method losses in excess of Company's interest																			72,000,000		45,300,000
Net loss of joint venture		$ 58,800,000																			52,500,000		36,200,000
Business combination, consideration transferred																			41,000,000
Net assets acquired											$ 16,000,000								16,000,000
Fair value of controlling interest obtained																			32,000,000
Research and Development [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Stock-based compensation expense																			23,273,000		17,557,000		8,800,000
License and Service [Member] | Casebia Therapeutics Limited Liability Partnership [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue																			$ 500,000		2,500,000		4,800,000
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] | Casebia Therapeutics Limited Liability Partnership [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Equity method investment, ownership percentage											50.00%								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
Number of options exercised under agreement | Option																			2
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								$ 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								4,800,000
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
Co-commercialization Agreement [Member] | Casebia Therapeutics Limited Liability Partnership [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percentage of research and development costs		50.00%
Percentage sharing of profit (loss) from sale of product		50.00%
2015 Casebia Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Equity method investment											0								0
2019 Casebia Agreement [Member] | Casebia Therapeutics Limited Liability Partnership [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Equity method investment											0								0
Fair value of assets and liabilities											16,000,000								16,000,000
2019 Casebia Agreement [Member] | Other Current Liabilities [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research obligation											11,000,000								11,000,000
2019 Casebia Agreement [Member] | Other Long-term Liabilities [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research obligation											14,000,000								14,000,000
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				57,800,000				11,800,000		57,800,000
Non-cash consideration received																			10,000,000
Transaction price allocated to remaining performance obligations											12,700,000								12,700,000
Collaboration revenue																			30,000,000
Revenue																			289,100,000		600,000		36,200,000
Current deferred revenue											900,000				$ 100,000				900,000		100,000
Research and development expense																			29,200,000		20,200,000		9,900,000
Reimbursements from research and license agreements																			15,900,000		13,800,000		0
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								420,000,000
Milestone payment receivable											410,000,000								410,000,000
Transaction price allocated to remaining performance obligations											46,700,000								46,700,000
Revenue																			76,700,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | DM1 R&D Services [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration																			1,700,000
Transaction price allocated to remaining performance obligations											1,100,000								1,100,000
Revenue																			100,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | DM1 R&D Services [Member] | Research and Development [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Variable consideration received																			800,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | DMD License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration																			224,600,000
Transaction price allocated to remaining performance obligations											151,100,000								151,100,000
Revenue																			289,100,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | DM1 License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration																			76,200,000
Transaction price allocated to remaining performance obligations											51,300,000								51,300,000
Revenue																			202,400,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Specified Target Option Material Right [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration																			17,500,000
Transaction price allocated to remaining performance obligations											11,800,000								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] | Waiving of Vertex’s Material Right [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue																			6,700,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Joint Development Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Up-front payment received																			$ 7,000,000
Agreement description																			In connection with the JDA, the Company received a $7.0 million up-front payment from Vertex and subsequently received a one-time low seven-digit milestone payment upon the dosing of the second patient in a clinical trial with the initial product candidate.
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Exercise of Exclusive Option [Member] | Collaboration Target Options [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable											10,000,000								$ 10,000,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Collaborative Arrangement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Nonrefundable upfront payment received																			175,000,000
Maximum potential future payments																			$ 825,000,000
Percentage of exchange payment of research and development costs																			50.00%
Collaborative arrangement, license rights reacquired by waiving payment owed																			$ 10,000,000
Non-cash consideration expensed upon execution of collaborative agreement																			10,000,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Collaborative Arrangement [Member] | Prepaid Expenses and Other Current Assets
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Contract asset											25,000,000								25,000,000
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								$ 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								$ 57,800,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | 2015 Collaboration Agreement [Member] | Collaborative Arrangement Material Rights Fourth Exclusive License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration																			10,000,000
Transaction price allocated to remaining performance obligations											6,700,000								6,700,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Revenue Related to Three Collaboration Target Options Material Right [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue																			10,000,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Beta Globin
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated standalone selling price for single collaboration																							$ 30,300,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Non-Exclusive Research License [Member] | Research And Development Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue																			$ 100,000		600,000
Vertex Pharmaceuticals Inc [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate amount in option exercise payments received											30,000,000
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] | 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
ViaCyte [Member] | Research Collaboration Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense																					15,000,000
Amount payable under collaboration agreement						$ 15,000,000
Number of installments for amount payable | Installment						2
Issuance of common shares | shares				214,512	165,636
Issuance of common shares, value				$ 8,100,000	$ 7,500,000
Key provisions of collaborative agreement description																			The agreement includes certain provisions such that in the event ViaCyte sold shares received from the Company for less than $15.0 million in combined net proceeds, the Company would owe ViaCyte the deficient amount. In the event ViaCyte sold shares received from the Company for greater than $15.0 million in combined net proceeds, ViaCyte would owe the Company the surplus amount.
Net proceeds from issuance of common shares									$ 7,500,000	$ 6,900,000
Deficient amount payable										$ 600,000
Deficient amount paid in cash			$ 600,000
Total consideration paid																					16,200,000
Other (expense) income																					$ (1,200,000)
Collaboration agreement period						6 years
ViaCyte [Member] | Research Collaboration Agreement [Member] | Convertible Promissory Note [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Additional amount payable under certain circumstances						$ 10,000,000
[1]	Including the following amounts of revenue from a related party, see Note 7
[2]	Including the following amounts of research and development from a related party, see Note 7

Significant Contracts - Schedul

Significant Contracts - Schedule of Fair Value of Assets and Liabilities Received (Detail) $ in Thousands	Dec. 31, 2019USD ($)
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						12 Months Ended
	Nov. 30, 2019USD ($)$ / sharesshares	Aug. 31, 2019USD ($)	Sep. 30, 2018USD ($)$ / sharesshares	Aug. 31, 2018USD ($)	Jan. 31, 2018USD ($)$ / sharesshares	Oct. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)	Dec. 31, 2019SFr / sharesshares	Dec. 31, 2018SFr / sharesshares
Class of Stock [Line Items]
Common stock, shares authorized | shares									103,901,006	90,343,803
Common shares, par value | SFr / shares									SFr 0.03	SFr 0.03
Capital reserved for future issuance | shares									1,230,729
Proceeds from issuance of common shares							$ 415,019,000	$ 307,053,000
Common Stock, Voting Rights							one vote for each Common Share
Dividends declared and paid							$ 0
IPO [Member]
Class of Stock [Line Items]
Common shares sold | shares						4,400,000
Common shares price per share | $ / shares						$ 14
Proceeds from issuance of common shares						$ 53,700,000
Equity issuance costs						$ 8,300,000
Private Placement [Member] | Bayer Global Investments B.V [Member]
Class of Stock [Line Items]
Common shares sold | shares						2,500,000
Common shares price per share | $ / shares						$ 14
Proceeds from issuance of common shares						$ 35,000,000
Underwritten Public Offering [Member]
Class of Stock [Line Items]
Common shares sold | shares			4,200,000		5,700,000
Common shares price per share | $ / shares			$ 47.50		$ 22.75
Proceeds from issuance of common shares			$ 184,500,000		$ 122,600,000
Equity issuance costs			$ 15,500,000		$ 8,200,000
Underwritten Public Offering [Member] | Sales Agreement With Jefferies LLC [Member]
Class of Stock [Line Items]
Common shares sold | shares	4,900,000
Common shares price per share | $ / shares	$ 64.50
Proceeds from issuance of common shares	$ 294,400,000
Equity issuance costs	$ 20,700,000
2018 ATM [Member] | Sales Agreement With Jefferies LLC [Member]
Class of Stock [Line Items]
Common shares sold | shares							2,800,000
Proceeds from issuance of common shares							$ 120,600,000
Equity issuance costs							$ 4,400,000
Average issue price of common shares | $ / shares							$ 44.38
2018 ATM [Member] | Sales Agreement With Jefferies LLC [Member] | Maximum [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds				$ 125,000,000
2019 ATM [Member] | Maximum [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds		$ 200,000,000

Share Capital - Schedule of Sha

Share Capital - Schedule of Share Capital (Detail) - shares	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Registered share capital	61,037,000	52,268,000
Authorized share capital	103,901,006	90,343,803
Employee Benefit Plans [Member]
Class of Stock [Line Items]
Conditional share capital - Bonds or similar debt instruments	18,698,000	15,579,000
Bonds or Similar Debt Instruments [Member]
Class of Stock [Line Items]
Conditional share capital - Bonds or similar debt instruments	4,920,000	4,920,000
Swiss Law [Member]
Class of Stock [Line Items]
Authorized share capital	19,246,000	17,577,000

Equity-based Compensation - Opt

Equity-based Compensation - Option and Grant Plans - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment award, number of shares granted	2,832,784	2,209,597	2,999,847
Option and Grant Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, options, vesting period	4 years
Share-based compensation, options, contractual life	10 years
Option and Grant Plans [Member] | IPO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment award, number of shares granted	0

Equity-based Compensation - Equ

Equity-based Compensation - Equity-Based Compensation Expense - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 49,524	$ 39,260	$ 20,636
Total unrecognized compensation expense related to stock options	96,200
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 31,900
Unrecognized compensation expense, remaining weighted-average period for recognition	2 years 3 months 18 days
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, remaining weighted-average period for recognition	2 years 9 months 18 days

Equity-based Compensation - Sch

Equity-based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock‑based compensation expense	$ 49,524	$ 39,260	$ 20,636
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock‑based compensation expense	23,273	17,557	8,800
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock‑based compensation expense	20,784	17,428	10,073
Loss from Equity Method Investment [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock‑based compensation expense	$ 5,467	$ 4,275	$ 1,763

Equity-based Compensation - Fai

Equity-based Compensation - Fair Value of Each Option Issued to Employees and Non-employees Estimated Using Black-Scholes Option-Pricing Model (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options granted	2,832,784	2,209,597	2,999,847
Weighted-average exercise price	$ 39.16	$ 51.73	$ 16.98
Weighted-average grant date fair value	$ 24.57	$ 33.82	$ 11.16
Expected volatility	68.90%	71.90%	72.50%
Expected term (in years)	6 years	6 years	6 years 1 month 6 days
Risk-free interest rate	2.20%	2.80%	2.00%
Expected dividend yield	0.00%	0.00%	0.00%

Equity-based Compensation - Sum

Equity-based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]
Shares, Outstanding, Beginning Balance	6,689,311
Shares, Granted	2,832,784	2,209,597	2,999,847
Shares, Exercised	(1,180,644)
Shares, Cancelled or forfeited	(559,014)
Shares, Outstanding, Ending Balance	7,782,437	6,689,311
Shares, Exercisable	3,328,398
Shares, Vested or expected to vest	7,782,437
Weighted-Average Exercise Price, Outstanding, Beginning Balance	$ 25.42
Weighted-Average Exercise Price, Granted	39.16	$ 51.73	$ 16.98
Weighted-Average Exercise Price, Exercised	14.91
Weighted-Average Exercise Price, Cancelled or forfeited	35.35
Weighted-Average Exercise Price, Outstanding, Ending Balance	31.30	$ 25.42
Weighted-Average Exercise Price, Exercisable	24.07
Weighted-Average Exercise Price, Vested or expected to vest	$ 31.30
Weighted-Average Remaining Contractual Term	8 years 2 months 12 days	8 years 3 months 18 days
Weighted-Average Remaining Contractual Term, Exercisable	7 years 4 months 24 days
Weighted-Average Remaining Contractual Term, Vested or expected to vest	8 years 2 months 12 days
Aggregate Intrinsic Value, Outstanding Balance	$ 231,554	$ 68,572
Aggregate Intrinsic Value, Exercisable	122,774
Aggregate Intrinsic Value, Vested or expected to vest	$ 231,554

Equity-based Compensation - Sto

Equity-based Compensation - Stock Options - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, options, outstanding	7,782,437	6,689,311
Stock Options, Granted	2,832,784	2,209,597	2,999,847
Total intrinsic value of stock options exercised	$ 42.2	$ 38.3	$ 12.3
Performance-Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options, Granted	0	0
Performance-Based [Member] | Vesting Percentage on First Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, options, vested		883,695
Share-based compensation, options, outstanding		261,888
Market-Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, options, vested	0
Stock Options, Granted	0	0	150,000
Market-Based [Member] | Vesting Percentage on First Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, requisite service period			3 years
Share-based compensation, vesting percentage			75.00%
Market-Based [Member] | Vesting Percentage on Second Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, requisite service period			4 years
Share-based compensation, vesting percentage			25.00%

Equity-based Compensation - S_2

Equity-based Compensation - Summary of Restricted Stock Activity (Detail) - Restricted Stock [Member]	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted common shares, Number of Shares, Beginning Balance | shares	327,342
Unvested restricted common shares, Number of Shares, Granted | shares	503,600
Unvested restricted common shares, Number of Shares, Vested | shares	(86,758)
Unvested restricted common shares, Number of Shares, Cancelled or forfeited | shares	(44,650)
Unvested restricted common shares, Number of Shares, Ending Balance | shares	699,534
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Beginning Balance | $ / shares	$ 36.72
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Granted | $ / shares	62.11
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Vested | $ / shares	20.38
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Cancelled or forfeited | $ / shares	44.50
Unvested restricted common shares, Weighted-Average Grant Date Fair Value, Ending Balance | $ / shares	$ 56.53

Equity-based Compensation - Res

Equity-based Compensation - Restricted Stock - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 49,524,000	$ 39,260,000	$ 20,636,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of restricted stock vested	3,600,000	11,300,000	8,300,000
Stock Options [Member] | Departing Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	100,000	3,800,000	2,200,000
Stock Options [Member] | Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,900,000	$ 0	$ 0

Net Income (Loss) Per Share A_3

Net Income (Loss) Per Share Attributable to Common Shareholders - Schedule of Computation of Basic and Diluted Net Income (Loss) per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic net income (loss) per common share calculation:
Net income (loss) attributable to common shareholders	$ 30,542	$ 138,423	$ (53,699)	$ (48,408)	$ (47,590)	$ (50,711)	$ (38,380)	$ (28,300)	$ 66,858	$ (164,981)	$ (68,357)
Net income (loss) attributable to common shareholders - basic									$ 66,858	$ (164,981)	$ (68,357)
Basic weighted-average common shares outstanding	57,395,839	54,829,057	53,188,041	52,093,208	51,688,383	47,391,988	46,842,316	45,877,428	54,392,304	47,964,368	40,057,365
Basic net income (loss) per common share	$ 0.53	$ 2.52	$ (1.01)	$ (0.93)	$ (0.92)	$ (1.07)	$ (0.82)	$ (0.62)	$ 1.23	$ (3.44)	$ (1.71)
Diluted net income (loss) per common share calculation:
Net income (loss) attributable to common shareholders	$ 30,542	$ 138,423	$ (53,699)	$ (48,408)	$ (47,590)	$ (50,711)	$ (38,380)	$ (28,300)	$ 66,858	$ (164,981)	$ (68,357)
Net income (loss) attributable to common shareholders - diluted									$ 66,858	$ (164,981)	$ (68,357)
Basic weighted-average common shares outstanding	57,395,839	54,829,057	53,188,041	52,093,208	51,688,383	47,391,988	46,842,316	45,877,428	54,392,304	47,964,368	40,057,365
Effect of potentially dilutive securities:
Weighted-average shares used to compute diluted net income (loss) per common share	60,233,927	57,598,901	53,188,041	52,093,208	51,688,383	47,391,988	46,842,316	45,877,428	56,932,798	47,964,368	40,057,365
Diluted net income (loss) per common share	$ 0.51	$ 2.40	$ (1.01)	$ (0.93)	$ (0.92)	$ (1.07)	$ (0.82)	$ (0.62)	$ 1.17	$ (3.44)	$ (1.71)
Outstanding Options [Member]
Effect of potentially dilutive securities:
Effect of potentially dilutive securities									2,406,962
Unvested Restricted Common Shares [Member]
Effect of potentially dilutive securities:
Effect of potentially dilutive securities									133,532

Net Income (Loss) Per Share A_4

Net Income (Loss) Per Share Attributable to Common Shareholders - Schedule of Antidilutive Securities not Include in Computation of Net Income (Loss) per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not include in computation of net income (loss) per share	3,897,754	7,016,653	6,419,854
Outstanding Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not include in computation of net income (loss) per share	3,789,129	6,689,311	6,262,339
Unvested Restricted Common Shares [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities not include in computation of net income (loss) per share	108,625	327,342	157,515

401(k) Savings Plan - Additiona

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Company contributions toward the plan	$ 1.1	$ 0.6	$ 0.5

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income (Loss) Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Domestic	$ 9,155	$ 5,966	$ 5,184
Foreign	58,151	(170,394)	(71,792)
Total	$ 67,306	$ (164,428)	$ (66,608)

Income Taxes - Schedule of (Pro

Income Taxes - Schedule of (Provision for) Benefit from Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current income taxes:
Federal	$ (423)	$ (416)	$ (1,533)
State	(59)	(131)	(42)
Foreign		0	6
Total current income taxes	(482)	(547)	(1,569)
Deferred income taxes:
Federal	34	(6)	(477)
State			297
Total deferred income taxes	34	(6)	(180)
Total income tax provision	$ (448)	$ (553)	$ (1,749)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Income Tax Expense Computed at Statutory Corporate Income Tax Rate to Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Effective Income Tax Rate
Income tax expense at statutory rate	9.30%	9.30%	9.30%
State income tax, net of federal benefit	(2.10%)	0.70%	0.30%
Nondeductible expenses	(0.10%)	0.00%	0.00%
Foreign rate differential	2.00%	(0.40%)	(2.50%)
Statutory to US GAAP permanent differences	0.10%	1.00%	1.80%
Stock-based compensation	(2.00%)	1.40%	(2.90%)
Impact of deferred rate change	(12.20%)	0.00%	0.00%
Research credits	(5.20%)	1.80%	0.80%
Change in valuation allowance	10.90%	(14.10%)	(9.40%)
Effective income tax rate	0.70%	(0.30%)	(2.60%)

Income Taxes - Schedule of Sign

Income Taxes - Schedule of Significant Components of Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 31,496	$ 25,418
Accruals and reserves	2,868	1,816
Operating lease liabilities	14,214
Deferred Rent		3,300
Other deferred tax assets	28	51
Stock-based compensation	5,217	2,871
Deferred revenue		3,264
Deferred revenue	(20)
Research credit	7,150	3,322
Total deferred tax assets	60,953	40,042
Less valuation allowance	(45,913)	(36,208)
Net deferred tax assets	15,040	3,834
Deferred tax liabilities:
Depreciation	(3,901)	(3,785)
Operating lease assets	(11,068)
Intangible assets	(40)	(49)
Other deferred tax liabilities	(20)	(22)
Total deferred tax liabilities	(15,029)	(3,856)
Long term deferred taxes, assets	$ 11
Long term deferred taxes, liabilities		$ (22)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance [Line Items]
Non-US Net operating loss carryforwards	$ 526,100,000
Operating loss carryforwards expiration period	2022
Unrecognized tax benefits, gross	$ 5,231,000	$ 1,595,000	$ 354,000	$ 163,000
Unrecognized tax benefits would favorably impact the effective tax rate if recognized	4,800,000
Accrued interest or penalties related to uncertain tax positions	0	0	0
Uncertain tax positions recognized	0	$ 0	$ 0
U.S. Domestic Federal [Member] | Research and Development [Member]
Valuation Allowance [Line Items]
Tax credit carryforward amount	$ 4,400,000
Tax credit carryforward, expiration year	2039
Uncertain tax positions	$ 3,000,000
U.S. Domestic State [Member] | Research and Development [Member]
Valuation Allowance [Line Items]
Tax credit carryforward amount	$ 3,400,000
Tax credit carryforward, expiration year	2034
Uncertain tax positions	$ 2,200,000
Switzerland [Member]
Valuation Allowance [Line Items]
Increase in valuation allowance	9,700,000
Non-US Net operating loss carryforwards	262,300,000
Canton of Zug [Member]
Valuation Allowance [Line Items]
Non-US Net operating loss carryforwards	262,300,000
UNITED KINGDOM [Member]
Valuation Allowance [Line Items]
Non-US Net operating loss carryforwards	$ 1,500,000

Income Taxes - Schedule of Aggr

Income Taxes - Schedule of Aggregate Changes in Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 1,595	$ 354	$ 163
Increases for tax positions taken during current period	2,754	1,212	178
Increases for tax positions taken in prior periods	882	29	13
Balance at end of year	$ 5,231	$ 1,595	$ 354

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Collaboration revenue	$ 77,016	$ 211,928	$ 318	$ 328	$ 115	$ 563	$ 1,088	$ 1,358	$ 289,590	[1]	$ 3,124	[1]	$ 40,997	[1]
Total operating expenses	66,033	72,765	55,301	48,751	45,343	49,995	38,374	28,355	242,850		162,067		105,645
(Loss) income from operations	10,983	139,163	(54,983)	(48,423)	(45,228)	(49,432)	(37,286)	(26,997)	46,740		(158,943)		(64,648)
Net income (loss)	$ 30,542	$ 138,423	$ (53,699)	$ (48,408)	$ (47,590)	$ (50,711)	$ (38,380)	$ (28,300)	$ 66,858		$ (164,981)		$ (68,357)
Net (loss) income per share attributable to common shareholders:
Basic	$ 0.53	$ 2.52	$ (1.01)	$ (0.93)	$ (0.92)	$ (1.07)	$ (0.82)	$ (0.62)	$ 1.23		$ (3.44)		$ (1.71)
Diluted	$ 0.51	$ 2.40	$ (1.01)	$ (0.93)	$ (0.92)	$ (1.07)	$ (0.82)	$ (0.62)	$ 1.17		$ (3.44)		$ (1.71)
Weighted-average common shares outstanding used in net (loss) income per share attributable to common shareholders:
Basic	57,395,839	54,829,057	53,188,041	52,093,208	51,688,383	47,391,988	46,842,316	45,877,428	54,392,304		47,964,368		40,057,365
Diluted	60,233,927	57,598,901	53,188,041	52,093,208	51,688,383	47,391,988	46,842,316	45,877,428	56,932,798		47,964,368		40,057,365
[1]	Including the following amounts of revenue from a related party, see Note 7

Related Party Transactions - Ad

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