CRISPR Therapeutics (CRSP) 10-Q 29 Jul 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Jul. 25, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Title of 12(b) Security	Common Shares, CHF 0.03 par value
Trading Symbol	CRSP
Security Exchange Name	NASDAQ Stock Market LLC
Entity Registrant Name	CRISPR THERAPEUTICS AG
Entity Central Index Key	0001674416
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		54,662,539
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-37923
Entity Address, Address Line One	Baarerstrasse 14
Entity Address, City or Town	Zug
Entity Address, Country	Switzerland
Entity Address, Postal Zip Code	6300
City Area Code	41 (0)41
Local Phone Number	561 32 77

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 427,885	$ 456,649
Accounts receivable, including related party amounts of $321 and $88 as of June 30, 2019 and December 31, 2018, respectively	321	88
Prepaid expenses and other current assets, including related party amounts of $3,318 and $3,417 as of June 30, 2019 and December 31, 2018, respectively	10,267	9,658
Total current assets	438,473	466,395
Property and equipment, net	20,156	18,500
Intangible assets, net	262	289
Restricted cash	3,915	3,163
Operating lease assets	30,770
Other non-current assets	669	669
Total assets	494,245	489,016
Current liabilities:
Accounts payable	7,143	5,069
Accrued expenses, including related party amounts of $3,312 and $1,700 as of June 30, 2019 and December 31, 2018, respectively	18,628	20,852
Accrued tax liabilities	542	402
Deferred rent		1,202
Operating lease liabilities	4,880
Other current liabilities	219	221
Total current liabilities	31,412	27,746
Deferred revenue non-current, including related party amounts of $57,730 and $57,780 as of June 30, 2019 and December 31, 2018, respectively	57,730	57,780
Deferred rent non-current		11,052
Operating lease liabilities, net of current portion	37,200
Other non-current liabilities	220	243
Total liabilities	126,562	96,821
Commitments and contingencies, see Note 4
Shareholders’ equity:
Common shares, CHF 0.03 par value, 55,445,241 and 52,183,139 shares authorized at June 30, 2019 and December 31, 2018, respectively, 53,756,046 and 52,160,798 shares issued at June 30, 2019 and December 31, 2018, respectively, 53,499,057 and 51,852,862 shares outstanding at June 30, 2019 and December 31, 2018, respectively, 23,948,128 and 20,498,996 shares in conditional capital at June 30, 2019 and December 31, 2018, respectively.	1,630	1,584
Treasury shares, at cost, 256,989 and 307,936 shares at June 30, 2019 and December 31, 2018, respectively	(57)	(57)
Additional paid-in capital	759,796	682,245
Accumulated deficit	(393,676)	(291,569)
Accumulated other comprehensive loss	(10)	(8)
Total shareholders' equity	367,683	392,195
Total liabilities and shareholders’ equity	$ 494,245	$ 489,016

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) $ in Thousands	Jun. 30, 2019USD ($)shares	Dec. 31, 2018USD ($)shares
Statement Of Financial Position [Abstract]
Accounts receivable, related party amount, current | $	$ 321	$ 88
Prepaid expenses and other current assets, related party amount | $	3,318	3,417
Accrued expenses related party amount, current | $	3,312	1,700
Deferred revenue non-current related party amount | $	$ 57,730	$ 57,780
Common stock, shares authorized	55,445,241	52,183,139
Common stock, shares issued	53,756,046	52,160,798
Common stock, shares outstanding	53,499,057	51,852,862
Common stock, conditional capital	23,948,128	20,498,996
Treasury stock, shares	256,989	307,936

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Collaboration revenue	[1]	$ 318	$ 1,088	$ 646	$ 2,446
Operating expenses:
Research and development	[2]	39,533	25,633	73,355	45,152
General and administrative		15,768	12,741	30,697	21,577
Total operating expenses		55,301	38,374	104,052	66,729
Loss from operations		(54,983)	(37,286)	(103,406)	(64,283)
Other income (expense):
Loss from equity method investment		(1,012)	(1,153)	(2,037)	(2,244)
Other income (expense), net		2,381	155	3,506	29
Total other income (expense), net		1,369	(998)	1,469	(2,215)
Net loss before income taxes		(53,614)	(38,284)	(101,937)	(66,498)
Provision for income taxes		(85)	(96)	(170)	(182)
Net loss		(53,699)	(38,380)	(102,107)	(66,680)
Foreign currency translation adjustment		(10)	(21)	(2)	(9)
Comprehensive loss		(53,709)	(38,401)	(102,109)	(66,689)
Reconciliation of net loss to net loss attributable to common shareholders:
Net loss		$ (53,699)	$ (38,380)	$ (102,107)	$ (66,680)
Net loss per share attributable to common shareholders—basic and diluted		$ (1.01)	$ (0.82)	$ (1.94)	$ (1.44)
Weighted-average common shares outstanding used in net loss per share attributable to common shareholders—basic and diluted		53,188,041	46,842,316	52,643,649	46,362,538
[1]	Including the following revenue from a related party, see Notes 6 & 11
[2]	Including the following research and development expense with a related party, see Notes 6 & 11

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenue from related party	$ 318	$ 881	$ 646	$ 1,963
Research and development expense with a related party	$ 6,870	$ 1,246	$ 14,459	$ 2,352

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Shares [Member]	Treasury Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2017	$ 187,832	$ 1,240		$ 312,018	$ (125,440)	$ 14
Beginning 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 shares, net of issuance costs	122,597	$ 174		122,423
Issuance of common shares, net of issuance costs (in shares)		5,750,000
Vesting of restricted shares	13			13
Vesting of restricted shares (in shares)		10,042
Exercise of vested options	2,656	$ 9		2,647
Exercise of vested options (in shares)		328,525	(6,253)
Stock-based compensation expense	6,673			6,673
Other comprehensive loss	12					12
Net loss	(28,300)				(28,300)
Ending balance at Mar. 31, 2018	290,335	$ 1,423		443,774	(154,888)	26
Ending balance (in shares) at Mar. 31, 2018		46,680,815	438,620
Beginning balance at Dec. 31, 2017	187,832	$ 1,240		312,018	(125,440)	14
Beginning balance (in shares) at Dec. 31, 2017		40,592,248	444,873
Net loss	(66,680)
Ending balance at Jun. 30, 2018	265,154	$ 1,435	$ (50)	457,032	(193,268)	5
Ending balance (in shares) at Jun. 30, 2018		47,071,835	409,361
Beginning balance at Mar. 31, 2018	290,335	$ 1,423		443,774	(154,888)	26
Beginning balance (in shares) at Mar. 31, 2018		46,680,815	438,620
Vesting of restricted shares	14	$ 1		13
Vesting of restricted shares (in shares)		10,043
Exercise of vested options	3,729	$ 11	$ (50)	3,768
Exercise of vested options (in shares)		380,977	(29,259)
Stock-based compensation expense	9,477			9,477
Other comprehensive loss	(21)					(21)
Net loss	(38,380)				(38,380)
Ending balance at Jun. 30, 2018	265,154	$ 1,435	$ (50)	457,032	(193,268)	5
Ending balance (in shares) at Jun. 30, 2018		47,071,835	409,361
Beginning balance at Dec. 31, 2018	392,195	$ 1,584	$ (57)	682,245	(291,569)	(8)
Beginning balance (in shares) at Dec. 31, 2018		51,852,862	307,936
Issuance of common shares, net of issuance costs	23,472			23,472
Issuance of common shares, net of issuance costs (in shares)		631,580
Vesting of restricted shares	15			15
Vesting of restricted shares (in shares)		9,288
Exercise of vested options	1,832	$ 5		1,827
Exercise of vested options (in shares)		141,915
Stock-based compensation expense	10,696			10,696
Other comprehensive loss	8					8
Net loss	(48,408)				(48,408)
Ending balance at Mar. 31, 2019	379,810	$ 1,589	$ (57)	718,255	(339,977)
Ending balance (in shares) at Mar. 31, 2019		52,635,645	307,936
Beginning balance at Dec. 31, 2018	$ 392,195	$ 1,584	$ (57)	682,245	(291,569)	(8)
Beginning balance (in shares) at Dec. 31, 2018		51,852,862	307,936
Exercise of vested options (in shares)	263,700
Net loss	$ (102,107)
Ending balance at Jun. 30, 2019	367,683	$ 1,630	$ (57)	759,796	(393,676)	(10)
Ending balance (in shares) at Jun. 30, 2019		53,499,057	256,989
Beginning balance at Mar. 31, 2019	379,810	$ 1,589	$ (57)	718,255	(339,977)
Beginning balance (in shares) at Mar. 31, 2019		52,635,645	307,936
Issuance of common shares, net of issuance costs	28,114	$ 40		28,074
Issuance of common shares, net of issuance costs (in shares)		732,108	(47,297)
Vesting of restricted shares	16	$ 1		15
Vesting of restricted shares (in shares)		12,317
Exercise of vested options	1,254			1,254
Exercise of vested options (in shares)		118,987	(3,650)
Stock-based compensation expense	12,198			12,198
Other comprehensive loss	(10)					(10)
Net loss	(53,699)				(53,699)
Ending balance at Jun. 30, 2019	$ 367,683	$ 1,630	$ (57)	$ 759,796	$ (393,676)	$ (10)
Ending balance (in shares) at Jun. 30, 2019		53,499,057	256,989

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parenthetical) $ in Millions	3 Months Ended
	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Jun. 30, 2019SFr / shares	Mar. 31, 2019SFr / shares	Jun. 30, 2018SFr / shares	Mar. 31, 2018SFr / shares
Common shares, par value					SFr 0.03
Common Shares [Member]
Issuance costs | $	$ 1.3	$ 1.2	$ 0	$ 8.2
Common shares, par value					SFr 0.03	SFr 0.03	SFr 0.03	SFr 0.03

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities:
Net loss	$ (102,107)	$ (66,680)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	2,010	1,691
Equity-based compensation	20,857	13,906
Loss from equity method investment	2,037	2,244
Other income, non-cash		(169)
Changes in:
Accounts receivable	(233)	1,682
Prepaid expenses and other assets	(1,399)	(3,804)
Accounts payable and accrued expenses	(849)	3,764
Deferred revenue	(50)	(244)
Deferred rent		(381)
Operating lease assets and liabilities	(391)
Other liabilities, net	6	88
Net cash used in operating activities	(80,119)	(47,903)
Investing activities:
Purchase of property and equipment	(3,271)	(1,078)
Net cash used in investing activities	(3,271)	(1,078)
Financing activities:
Proceeds from issuance of common shares, net of issuance costs	52,294	122,597
Proceeds from exercise of options	3,086	6,433
Repurchase of treasury shares		(50)
Net cash provided by financing activities	55,380	128,980
Effect of exchange rate changes on cash	(2)	(9)
(Decrease) increase in cash	(28,012)	79,990
Cash, cash equivalents and restricted cash, beginning of period	459,812	242,912
Cash, cash equivalents and restricted cash, end of period	431,800	322,902
Supplemental disclosure of non-cash investing and financing activities
Property and equipment purchases in accounts payable and accrued expenses	702	$ 125
Equity issuance costs in accounts payable and accrued expenses	$ 477

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Reconciliation to amounts within the condensed consolidated balance sheets
Cash and cash equivalents	$ 427,885	$ 456,649	$ 319,737
Restricted cash	3,915	3,163	3,165
Cash, cash equivalents and restricted cash at end of period	$ 431,800	$ 459,812	$ 322,902	$ 242,912

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	1. Basis of Presentation and Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements are unaudited and have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company views its operations and manages its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology. Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the financial position and results of operations for the three and six month interim periods ended June 30, 2019 and 2018. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements for the year ended December 31, 2018, which are contained in the 2018 Annual Report on Form 10-K filed with the Securities and Exchange Commission (“SEC”) on February 25, 2019. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates in these consolidated financial statements have been made in connection with the calculation of revenues, research and development expenses and equity-based compensation expense. The Company bases its estimates on historical experience and various other assumptions, including, in certain circumstances, future projections that management believes to be reasonable. Actual results could differ from those estimates. Changes in estimates are reflected in reported results in the period in which they become known. Significant Accounting Policies The significant accounting policies used in preparation of these condensed consolidated financial statements for the three and six months ended June 30, 2019 are consistent with those discussed in Note 2 to the consolidated financial statements in the Company’s 2018 Annual Report on Form 10-K filed with the SEC on February 25, 2019, except with respect to the Company’s lease accounting policy noted within the “Recently adopted accounting standards” section below. Recently Adopted Accounting Standards The Company adopted ASC 842, Leases 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

Property and Equipment, net	6 Months Ended
	Jun. 30, 2019
Property Plant And Equipment [Abstract]
Property and Equipment, net	2. Property and Equipment, net Property and equipment, net, consists of the following (in thousands): As of June 30, December 31, 2019 2018 Computer equipment $ 585 $ 443 Furniture, fixtures and other 2,555 2,453 Laboratory equipment 10,157 8,964 Leasehold improvements 14,937 13,776 Construction work in process 1,280 239 Total property and equipment, gross 29,514 25,875 Accumulated depreciation (9,358 ) (7,375 ) Total property and equipment, net $ 20,156 $ 18,500 Depreciation expense for the three and six months ended June 30, 2019 was $1.0 million and $2.0 million, respectively. Depreciation expense for the three and six months ended June 30, 2018 was $0.9 million and $1.7 million, respectively.

Accrued Expenses

Accrued Expenses	6 Months Ended
	Jun. 30, 2019
Payables And Accruals [Abstract]
Accrued Expenses	3. Accrued Expenses Accrued expenses consist of the following (in thousands): As of June 30, December 31, 2019 2018 Payroll and employee-related costs $ 5,604 $ 7,321 Research costs 9,266 7,973 Licensing fees — 625 Professional fees 2,096 1,848 Intellectual property costs 1,164 2,193 Accrued property and equipment 387 294 Other 111 598 Total $ 18,628 $ 20,852

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	4. Commitments and Contingencies Litigation 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. As disclosed in its Current Report on Form 8-K filed with the SEC on June 26, 2019, on June 25, 2019, the Company received notification that the United States Patent and Trademark Office initiated an interference proceeding at the Patent Trial and Appeal Board (the “PTAB”) between certain pending U.S. patent applications co-owned by the University of California, the University of Vienna and Dr. Emmanuelle Charpentier (collectively, the “CVC Group”) and certain patents and a patent application currently owned by the Broad Institute and Massachusetts Institute of Technology and, in some instances, the President and Fellows of Harvard College (individually and collectively, the “Broad”), all of which are related to the single guide format of CRISPR/Cas9 genome editing technology in eukaryotic cells. The Company has an exclusive worldwide license in the field of human therapeutics to Dr. Charpentier’s rights as a co-owner of the CVC Group portfolio. Specifically, the PTAB has declared Patent Interference No. 106,115 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; and 16/136,175, 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. Letters of Credit As of June 30, 2019, the Company had restricted cash of $3.9 million 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. The cash deposit is recorded in restricted cash in the accompanying consolidated balance sheet as of June 30, 2019. Research Agreements The Company has engaged several research institutions and companies to identify new delivery strategies and applications of its gene-editing technology. The Company is also a party to a number of research license agreements which require significant upfront payments, future royalty payments and potential milestone payments from time to time, as well as intellectual property agreements, which require maintenance and milestone payments from time to time. In association with these agreements, the Company has committed to making payments of $1.7 million and $2.1 million in 2019 and 2020, respectively. For the three and six months ended June 30, 2019, the Company paid $0.5 million and $2.2 million, respectively, related to these research agreements. The Company is also a party to a number of manufacturing agreements that require upfront payments for the future performance of services. In connection with these agreements, the Company paid $2.8 million in upfront payments, which were recorded as prepaid expenses as of June 30, 2019. The Company will amortize the prepaid balance as services are performed.

Leases

Leases	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Leases	5. Leases In June 2015, the Company entered into a lease agreement for the lease of approximately 19,817 square feet of research facility space with a commencement date of November 15, 2015 (the “2015 Lease”). The lease expires in February 2022. The 2015 Lease contains escalating rent clauses which require higher rent payments in future years. 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, and the Company has an option to extend the term of sublease for an additional five-year period if, at the time of expiration of the initial term, the sublessor does not intend to utilize the space for itself or its affiliates. The 2016 Sublease contains escalating rent clauses which require higher rent payments in future years. With the adoption of ASC 842, 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 period under the option. In May 2019, the Company entered into a lease agreement for the lease of approximately 15,877 square feet of office facility space with a commencement date of June 1, 2019 (the “2019 Lease”). The lease expires in November 2026, and the Company has an option to extend the term of the lease for an additional five-year period based on certain conditions within the Company’s control. The 2019 Lease contains escalating rent clauses which require higher rent payments in future years. At lease commencement, the Company recorded a right-of-use asset and corresponding lease liability. The right-of-use asset and corresponding lease liability does not include the additional five-year period under the 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 June 30, 2019 (in thousands): As of June 30, 2019 Assets Operating lease assets $ 30,770 Total lease assets 30,770 Liabilities Current Operating lease liabilities 4,880 Non-current Operating lease liabilities, net of current portion 37,200 Total lease liabilities $ 42,080 The following table summarizes operating lease costs included in research and development and general and administrative expense, as well as sublease income for the three and six months ended June 30, 2019 (in thousands): Three months ended June 30, 2019 Six months ended June 30, 2019 Operating lease costs $ 1,904 $ 3,726 Short-term lease costs 1,123 2,261 Variable lease costs 683 1,413 Sublease income — (525 ) Net lease cost $ 3,710 $ 6,875 The following table summarizes the maturity of undiscounted payments due under lease liabilities and the present value of those liabilities as of June 30, 2019 (in thousands): Total 2019 $ 4,419 2020 8,566 2021 8,507 2022 7,345 2023 7,362 Thereafter 23,254 Total $ 59,453 Present value adjustment (17,373 ) Present value of lease liabilities $ 42,080 The following table summarizes the lease term and discount rate as of June 30, 2019: As of June 30, 2019 Weighted-average remaining lease term (years) Operating leases 7.0 Weighted-average discount rate Operating leases 9.8 % The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the six months ended June 30, 2019 (in thousands): Six months ended June 30, 2019 Cash paid for amounts included in the measurement of lease liabilities $ 3,940 Operating cash flows from operating leases $ 3,940

Significant Contracts

Significant Contracts	6 Months Ended
	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Significant Contracts	6. Significant Contracts Collaboration Agreement with and Joint Development Agreement with Vertex Pharmaceuticals Incorporated and certain of its subsidiaries Summary of Agreement 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 will 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. For other targets that Vertex elects to license, Vertex will lead development and global commercialization activities. For each of up to four remaining targets that Vertex elects to license, the Company has the potential to receive up to $420.0 million in development, regulatory and commercial milestones and royalties on net product sales. In connection with the JDA, the Company received a $7.0 million up-front payment from Vertex and is eligible for a one-time low seven-digit milestone payment upon the dosing of the second patient in a clinical trial with the initial product candidate. The net profits and net losses, as applicable, incurred under the JDA will be shared equally between the Company and Vertex. Accounting for the 2015 Collaboration Agreement, Amendment No. 1 and JDA The arrangements include components of a customer-vendor relationship and collaborative arrangements as defined under ASC 808, Collaborative Arrangements Revenue from Contracts with Customers Accounting Analysis Under ASC 606 As the overall arrangement was modified in December 2017, the Company elected a practical expedient within ASC 606 that allowed entities to reflect the aggregate effect of all contract modifications when identifying the satisfied and unsatisfied performance obligations for contracts that were modified prior to the adoption of ASC 606. As of the December 2017 contract modification date, the Company concluded the arrangement contained the following 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 research and development (“R&D Services”). 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 2015 Collaboration Agreement and JDA 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 ESSP for material rights was determined based on the incremental discount given to Vertex based on the ESSP of the four remaining exclusive licenses and the exercise price paid at the time of exercise. 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 recognizes revenue related to the R&D Services as invoiced, in line with the practical expedient in ASC 606-10-55-18. The 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 R&D Services revenue is recognized as invoiced and specifically allocated to the R&D Services performance obligation. The remaining transaction price of $82.0 million was allocated among the performance obligations using the relative selling price method as follows: (i) a non-exclusive research license: $0.5 million; (ii) a material right to discounts for exclusive licenses for up to four Collaboration Targets: $22.2 million, $18.7 million, $8.4 million and $8.4 million for a total of $57.7 million; and (iii) co-exclusive development and commercialization licenses for hemoglobinopathy and beta-globin targets identified in the JDA and co-exclusive research license for the follow-on products: $23.8 million. The Company recognized $0.1 million and $0.2 million of revenue related to the collaboration with Vertex for the three and six months ended June 30, 2019, respectively. The Company recognized $0.2 million and $0.4 million of revenue related to the collaboration with Vertex for the three and six months ended June 30, 2018. As of June 30, 2019, there was $57.7 million of non-current deferred revenue related to the collaboration with Vertex compared to $57.8 as of December 31, 2018. The transaction price allocated to the remaining performance obligations is $57.8 million. The remaining performance obligations will be recognized as follows: four material rights to obtain an exclusive commercialization and development license at a point in time, upon exercise; and the non-exclusive research license ratably over/within the remaining research term. As of June 30, 2019, the remaining amount to be recognized for the non-exclusive research license is not significant. R&D Services are recognized as invoiced under the practical expedient and, as such, are not disclosed within the remaining performance obligation balance. Milestones under the 2015 Collaboration Agreement The Company evaluated the milestones that may be received in connection with the 2015 Collaboration Agreement and JDA. The first potential milestone the Company will be entitled to receive is the milestone in the JDA to receive a one-time low seven-digit milestone payment upon the dosing of a second patient in a clinical trial with the initial shared product and was fully constrained as of June 30, 2019 . T he remaining milestones are predominately related to the development and commercialization of a product resulting from the arrangement and are payable with respect to each selected exclusive license which have yet to be exercised and are not currently included in the determination of the transaction price. 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. There are nine remaining clinical development and regulatory approval milestones which may trigger proceeds of up to $ 90.0 million and $ 235.0 million, respectively, for each selected exclusive license, and two commercial milestones which may trigger proceeds of up to $ 75.0 million for each selected exclusive license (which, when combined with the $ 10.0 million due upon exercise of the exclusive option and the $ 10.0 million development milestone associated with an Investigational New Drug- enabling application, total $ 420.0 million for each selected Exclusive License), as follows: Developmental Milestone Events 1. Initiation of the first Clinical Trial of a Product; 2. Establishment of Proof of Concept for a Product; 3. Initiation of the first Phase 3 Clinical Trial of a Product; 4. Acceptance of Approval Application by the U.S. Food and Drug Administration for a Product; 5. Acceptance of Approval Application by the European Medicines Agency for a Product; 6. Acceptance of Approval Application by a Regulatory Authority in Japan for a Product; 7. Marketing Approval in the U.S. for a Product; 8. Marketing Approval in the EU for a Product; and 9. Marketing Approval in Japan for a Product. Commercial Milestone Events 1. Annual Net Sales for Products with respect to a Collaboration Target exceed $500 million; and 2. Annual Net Sales for Products with respect to a Collaboration Target exceed $1.0 billion. There is uncertainty that the events to obtain the developmental milestones will be achieved given the nature of clinical development and the stage of the CRISPR/Cas9 technology. Upon exercise of the exclusive license options, developmental milestones will be constrained until the Company is sure 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 The Company identified the following collaborative elements which 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. The Company recognized $6.6 million and $13.7 million of research and development expense related to the collaboration with Vertex for the three and six months ended June 30, 2019, respectively. The Company recognized $0.2 million and $0.4 million of research and development expense related to the collaboration with Vertex for the three and six months ended June 30, 2018, respectively. Research and development expense for the three and six months ended June 30, 2019 was net of $3.3 million and $7.8 million of reimbursements from Vertex, respectively. Research and development expense for the three and six months ended June 30, 2018 was net of $3.7 million and $6.9 million of reimbursements from Vertex, respectively. Joint Venture with Bayer Healthcare LLC On December 19, 2015, the Company entered into an agreement with Bayer Healthcare LLC and its subsidiaries (“Bayer”), to establish a joint venture to focus on the research 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 Therapeutics LLP (“Casebia”). Bayer and the Company each received a 50% equity interest in the entity in exchange for their respective contributions to the entity. The Company contributed $0.1 million in cash and licensed its proprietary CRISPR/Cas9 gene editing technology and intellectual property for selected disease indications. Bayer contributed its protein engineering expertise and relevant disease know-how. Under the agreement, Casebia paid the Company $35.0 million in exchange for a worldwide, exclusive license to commercialize the Company’s gene-editing technology specifically for the indications covered by the license. There are no milestone, royalties or other payments due to the Company under this aspect of the agreement. The Company also entered into a separate services agreement with Casebia, under which the Company agreed to provide compensated research and development services. During 2016, the Company recorded an equity method investment of $36.5 million equal to the fair value of the Company’s interest in Casebia and subsequently recorded unrealized equity method losses for the same amount. The Company has no further contractual obligations to provide cash financing to Casebia and accordingly, no additional losses have been recorded beyond the initial equity amount. Casebia’s net losses were $18.1 million and $32.3 million for the three and six months ended June 30, 2019, respectively. Casebia’s net losses were $13.5 million and $25.8 million for the three and six months ended June 30, 2018, respectively. Unrecognized equity method losses in excess of the Company’s equity investment in Casebia were $60.5 million and $45.3 million as of June 30, 2019 and December 31, 2018, respectively. The remaining performance obligations include research and development services, which are recorded as revenue under ASC 606 and cost sharing activities with Casebia related to shared research and technology licenses are accounted for as a cost/profit sharing arrangement under ASC 808, with the related impact of the cost sharing included as research and development expense. During the three and six months ended June 30, 2019, the Company recognized $0.2 million and $0.4 million of revenue, respectively, related to the collaboration with Casebia. During the three and six months ended June 30, 2018, the Company recognized $0.9 million and $2.0 million of revenue, respectively, related to the collaboration with Casebia. During the three and six months ended June 30, 2019, the Company recognized $0.2 million and $0.7 million, respectively, of research and development expense related to the collaboration with Casebia. During the three and six months ended June 30, 2018, the Company recognized $1.2 million and $2.4 million, respectively, of research and development expense related to the collaboration with Casebia. During the three and six months ended June 30, 2019, the Company recognized a loss from equity method investment of $1.0 million and $2.0 million, respectively, related to stock-based compensation expense for Casebia employees. During the three and six months ended June 30, 2018, the Company recognized a loss from equity method investment of $1.2 million and $2.2 million, respectively, related to stock-based compensation expense for Casebia employees.

Share Capital

Share Capital	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Share Capital	7. Share Capital The Company had 55,445,241 authorized common shares as of June 30, 2019, with a par value of CHF 0.03 per share. Included in the authorized common shares as of June 30, 2019 are 5,586 shares of unvested restricted stock awards, 256,989 treasury shares which are legally outstanding but not considered outstanding for accounting purposes and 1,683,609 shares registered and reserved for future issuance. The Company had conditional capital reserved for future issuance of 19,028,428 common shares for employee benefit plans and 4,919,700 common shares for debt instruments as of June 30, 2019. Under Swiss law, authorized share capital consisted of 25,134,003 common shares as of June 30, 2019. At-the-Market Offering In August 2018, the Company entered into an Open Market Sale Agreement SM

Stock-based Compensation

Stock-based Compensation	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	8. Stock-based Compensation During the three and six months ended June 30, 2019 and 2018, the Company recognized the following stock-based compensation expense (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 5,913 $ 5,167 $ 10,875 $ 8,083 General and administrative 5,273 3,157 9,982 5,823 Loss from equity method investment 1,012 1,153 2,037 2,244 Total $ 12,198 $ 9,477 $ 22,894 $ 16,150 Stock option activity The following table summarizes stock option activity for the six months ended June 30, 2019 (intrinsic value in thousands): Stock Options 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 1,948,773 $ 36.05 Exercised (263,700 ) $ 12.23 Cancelled or forfeited (178,518 ) $ 33.48 Outstanding at June 30, 2019 8,195,866 $ 28.19 8.3 $ 167,076 Exercisable at June 30, 2019 3,198,255 $ 19.51 7.5 $ 91,777 Vested and expected to vest at June 30, 2019 8,195,866 $ 28.19 8.3 $ 167,076 The Company estimated the fair value of each stock option award using the Black-Scholes option-pricing model based on the following assumptions: Six Months Ended June 30, 2019 2018 Assumptions Weighted-average expected volatility 69.3 % 72.2 % Expected term (in years) 6.0 6.0 Risk-free interest rate 2.5 % 2.7 % Expected dividend yield 0.0 % 0.0 % As of June 30, 2019, total unrecognized compensation expense related to stock options was $104.3 million which the Company expects to recognize over a remaining weighted-average period of 2.9 years. In May 2018, the Company modified the terms of certain options held by a departing employee. The modification resulted in $2.2 million in stock-based compensation expense recorded during the period. Restricted s tock activity The following table summarizes restricted stock activity for the six months ended June 30, 2019: Restricted Stock Weighted- Average Grant Date Fair Value Unvested balance as of December 31, 2018 327,342 $ 36.72 Granted 49,000 33.30 Vested (24,339 ) 14.96 Cancelled or forfeited (14,000 ) 38.33 Unvested balance as of June 30, 2019 338,003 $ 37.72 As of June 30, 2019, total unrecognized compensation expense related to unvested restricted common shares was $8.0

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Shareholders	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Shareholders	9. 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 common share equivalents, presented on an as-converted basis, were excluded from the calculation of net loss per share for the periods presented due to their anti-dilutive effect (in common share equivalent shares): As of June 30, 2019 June 30, 2018 Outstanding options 8,195,866 6,617,181 Unvested restricted common shares 338,003 169,930 Total 8,533,869 6,787,111

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes During the three and six months ended June 30, 2019, the Company recorded an income tax provision of $0.1 million and $0.2 million, respectively, representing an effective tax rate of -0.2% and -0.2%, respectively. During the three and six months ended June 30, 2018, the Company recorded an income tax provision of $0.1 million and $0.2 million, respectively, representing an effective tax rate of -0.3% and -0.3%, respectively. The income tax provision is primarily attributable to the year-to-date pre-tax income earned by the Company’s U.S. subsidiary. The difference in the statutory tax rate and effective tax rate is primarily a result of the jurisdictional mix of earnings and losses that are not benefited. The Company maintains a valuation allowance against certain deferred tax assets that are not more-likely-than-not realizable. As a result, the Company has not recognized a tax benefit related to losses generated in Switzerland in the current periods.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2019
Related Party Transactions [Abstract]
Related Party Transactions	11. Related Party Transactions In the fourth quarter of 2018, upon becoming an owner of record of more than 10% of the voting interest of the Company, Vertex became a related party under ASC 850, Related party disclosures “Collaboration Agreement with and Joint Development Agreement with Vertex Pharmaceuticals Incorporated and certain of its subsidiaries Joint Venture with Bayer Healthcare LLC

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2019
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events In June 2019, the Company and Vertex entered into a series of agreements, which closed on July 23, 2019. The Company entered into a strategic collaboration and license agreement (the “2019 Collaboration Agreement”) with Vertex 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 million. In addition, the Company is eligible to receive potential future payments of up to $825 million based upon the successful achievement of specified research, development, regulatory and commercial milestones for the DMD and DM1 programs. T he 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 and Vertex will share research costs for specified guide RNA research to be conducted by the Company, and Vertex is responsible for all other research, development, manufacturing and commercialization costs. Upon Investigational New Drug application filing, the Company has the option to forego the DM1 milestones and royalties to co-develop and co-commercialize all DM1 products globally . 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 final 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 conduct research and development activities for a specified target. Vertex will have the option to co-develop and co-commercialize the specified target and if Vertex does not exercise its option to do so within a specified time period, Vertex is eligible to receive potential specified research, development, regulatory and commercial milestones and tiered single-digit royalties on future net sales.

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements are unaudited and have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company views its operations and manages its business in one operating segment, which is the business of discovering, developing and commercializing therapies derived from or incorporating genome-editing technology. Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the financial position and results of operations for the three and six month interim periods ended June 30, 2019 and 2018. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements for the year ended December 31, 2018, which are contained in the 2018 Annual Report on Form 10-K filed with the Securities and Exchange Commission (“SEC”) on February 25, 2019.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates in these consolidated financial statements have been made in connection with the calculation of revenues, research and development expenses and equity-based compensation expense. The Company bases its estimates on historical experience and various other assumptions, including, in certain circumstances, future projections that management believes to be reasonable. Actual results could differ from those estimates. Changes in estimates are reflected in reported results in the period in which they become known.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards The Company adopted ASC 842, Leases 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.

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2019
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)	6 Months Ended
	Jun. 30, 2019
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net, consists of the following (in thousands): As of June 30, December 31, 2019 2018 Computer equipment $ 585 $ 443 Furniture, fixtures and other 2,555 2,453 Laboratory equipment 10,157 8,964 Leasehold improvements 14,937 13,776 Construction work in process 1,280 239 Total property and equipment, gross 29,514 25,875 Accumulated depreciation (9,358 ) (7,375 ) Total property and equipment, net $ 20,156 $ 18,500

Accrued Expenses (Tables)

Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2019
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): As of June 30, December 31, 2019 2018 Payroll and employee-related costs $ 5,604 $ 7,321 Research costs 9,266 7,973 Licensing fees — 625 Professional fees 2,096 1,848 Intellectual property costs 1,164 2,193 Accrued property and equipment 387 294 Other 111 598 Total $ 18,628 $ 20,852

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Summary of Lease Assets and Liabilities	The following table summarizes the lease assets and liabilities as of June 30, 2019 (in thousands): As of June 30, 2019 Assets Operating lease assets $ 30,770 Total lease assets 30,770 Liabilities Current Operating lease liabilities 4,880 Non-current Operating lease liabilities, net of current portion 37,200 Total lease liabilities $ 42,080
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 three and six months ended June 30, 2019 (in thousands): Three months ended June 30, 2019 Six months ended June 30, 2019 Operating lease costs $ 1,904 $ 3,726 Short-term lease costs 1,123 2,261 Variable lease costs 683 1,413 Sublease income — (525 ) Net lease cost $ 3,710 $ 6,875
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 June 30, 2019 (in thousands): Total 2019 $ 4,419 2020 8,566 2021 8,507 2022 7,345 2023 7,362 Thereafter 23,254 Total $ 59,453 Present value adjustment (17,373 ) Present value of lease liabilities $ 42,080
Summary of Lease Term and Discount Rate	The following table summarizes the lease term and discount rate as of June 30, 2019: As of June 30, 2019 Weighted-average remaining lease term (years) Operating leases 7.0 Weighted-average discount rate Operating leases 9.8 %
Summary of Cash Paid for Amounts Included in Measurement of Lease Liabilities	The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the six months ended June 30, 2019 (in thousands): Six months ended June 30, 2019 Cash paid for amounts included in the measurement of lease liabilities $ 3,940 Operating cash flows from operating leases $ 3,940

Stock-based Compensation (Table

Stock-based Compensation (Tables)	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock-Based Compensation Expense	During the three and six months ended June 30, 2019 and 2018, the Company recognized the following stock-based compensation expense (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 5,913 $ 5,167 $ 10,875 $ 8,083 General and administrative 5,273 3,157 9,982 5,823 Loss from equity method investment 1,012 1,153 2,037 2,244 Total $ 12,198 $ 9,477 $ 22,894 $ 16,150
Summary of Stock Option Activity	The following table summarizes stock option activity for the six months ended June 30, 2019 (intrinsic value in thousands): Stock Options 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 1,948,773 $ 36.05 Exercised (263,700 ) $ 12.23 Cancelled or forfeited (178,518 ) $ 33.48 Outstanding at June 30, 2019 8,195,866 $ 28.19 8.3 $ 167,076 Exercisable at June 30, 2019 3,198,255 $ 19.51 7.5 $ 91,777 Vested and expected to vest at June 30, 2019 8,195,866 $ 28.19 8.3 $ 167,076
Assumptions to Estimate Fair Value of Stock Option Award Using the Black-Scholes Option-Pricing Model	The Company estimated the fair value of each stock option award using the Black-Scholes option-pricing model based on the following assumptions: Six Months Ended June 30, 2019 2018 Assumptions Weighted-average expected volatility 69.3 % 72.2 % Expected term (in years) 6.0 6.0 Risk-free interest rate 2.5 % 2.7 % Expected dividend yield 0.0 % 0.0 %
Summary of Restricted Stock Activity	The following table summarizes restricted stock activity for the six months ended June 30, 2019: Restricted Stock Weighted- Average Grant Date Fair Value Unvested balance as of December 31, 2018 327,342 $ 36.72 Granted 49,000 33.30 Vested (24,339 ) 14.96 Cancelled or forfeited (14,000 ) 38.33 Unvested balance as of June 30, 2019 338,003 $ 37.72

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Shareholders (Tables)	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Calculation of Net Loss per Share	The following common share equivalents, presented on an as-converted basis, were excluded from the calculation of net loss per share for the periods presented due to their anti-dilutive effect (in common share equivalent shares): As of June 30, 2019 June 30, 2018 Outstanding options 8,195,866 6,617,181 Unvested restricted common shares 338,003 169,930 Total 8,533,869 6,787,111

Basis of Presentation and Sig_4

Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Net lease assets	$ 30,770
Net lease liabilities	$ 42,080
ASC 842 [Member]
Summary Of Significant Accounting Policies [Line Items]
Net lease assets		$ 26,087
Net lease liabilities		$ 37,600

Basis of Presentation and Sig_5

Basis of Presentation and Significant Accounting Policies - Impact of Adopting ASC 842 on Financial Statements (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Prepaid expenses and other current assets	$ 10,267		$ 9,658
Operating lease assets	30,770
Deferred rent			1,202
Deferred rent non-current			$ 11,052
Operating lease liabilities	4,880
Non-current operating lease liabilities	$ 37,200
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

Basis of Presentation and Sig_6

Basis of Presentation and Significant Accounting Policies - Impact of Adopting ASC 842 on Financial Statements (Parenthetical) (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 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	Jun. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 29,514	$ 25,875
Accumulated depreciation	(9,358)	(7,375)
Total property and equipment, net	20,156	18,500
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	585	443
Furniture, Fixtures and Other [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	2,555	2,453
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	10,157	8,964
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	14,937	13,776
Construction Work in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 1,280	$ 239

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Property Plant And Equipment [Abstract]
Depreciation expense	$ 1	$ 0.9	$ 2	$ 1.7

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Liabilities Current [Abstract]
Payroll and employee-related costs	$ 5,604	$ 7,321
Research costs	9,266	7,973
Licensing fees		625
Professional fees	2,096	1,848
Intellectual property costs	1,164	2,193
Accrued property and equipment	387	294
Other	111	598
Total	$ 18,628	$ 20,852

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019
Contingencies And Commitments [Line Items]
Research and development expense	[1]	$ 39,533	$ 25,633	$ 73,355	$ 45,152
Research Agreements [Member]
Contingencies And Commitments [Line Items]
Research and development expense		500		2,200
Research Agreements [Member] | Scenario Forecast [Member]
Contingencies And Commitments [Line Items]
Research and development expense						$ 2,100	$ 1,700
Manufacturing Agreements [Member] | Prepaid Expenses [Member]
Contingencies And Commitments [Line Items]
Upfront payment recorded as prepaid expense		2,800		2,800
Letter of Credit [Member]
Contingencies And Commitments [Line Items]
Letters of credit secured by cash held in restricted depository account		$ 3,900		$ 3,900
[1]	Including the following research and development expense with a related party, see Notes 6 & 11

Leases - Additional Information

Leases - Additional Information (Detail) - ft²	1 Months Ended			6 Months Ended
	May 31, 2019	May 31, 2016	Jun. 30, 2015	Jun. 30, 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 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
Operating Lease, Research Facility Space [Member]
Lessee Lease Description [Line Items]
Leased space			19,817
Operating Lease, Office Facility Space [Member]
Lessee Lease Description [Line Items]
Leased space	15,877

Leases - Summary of Lease Asset

Leases - Summary of Lease Assets and Liabilities (Detail) $ in Thousands	Jun. 30, 2019USD ($)
Assets
Operating lease assets	$ 30,770
Total lease assets	30,770
Liabilities
Operating lease liabilities, current	4,880
Operating lease liabilities, net of current portion	37,200
Total lease liabilities	$ 42,080

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	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease costs	$ 1,904	$ 3,726
Short-term lease costs	1,123	2,261
Variable lease costs	683	1,413
Sublease income		(525)	$ (176)
Net lease cost	$ 3,710	$ 6,875

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	Jun. 30, 2019USD ($)
Leases [Abstract]
2019	$ 4,419
2020	8,566
2021	8,507
2022	7,345
2023	7,362
Thereafter	23,254
Total	59,453
Present value adjustment	(17,373)
Present value of lease liabilities	$ 42,080

Leases - Summary of Lease Term

Leases - Summary of Lease Term and Discount Rate (Detail)	Jun. 30, 2019
Leases [Abstract]
Operating leases, weighted-average remaining lease term (years)	7 years
Operating leases, weighted-average discount rate	9.80%

Leases - Summary of Cash Paid f

Leases - Summary of Cash Paid for Amounts Included in Measurement of Lease Liabilities (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 3,940
Operating cash flows from operating leases	$ 3,940

Significant Contracts - Additio

Significant Contracts - Additional Information (Detail)		Feb. 12, 2016USD ($)	Oct. 26, 2015USD ($)Milestone	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2016USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue	[1]			$ 318,000	$ 1,088,000	$ 646,000	$ 2,446,000
Non-current deferred revenue				57,730,000		57,730,000		$ 57,780,000
Research and development expense	[2]			39,533,000	25,633,000	$ 73,355,000	45,152,000
Date of joint venture agreement						Dec. 19, 2015
Equity method investment									$ 36,500,000
Unrealized equity method losses				1,012,000	1,153,000	$ 2,037,000	2,244,000		$ 36,500,000
Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue				200,000	900,000	400,000	2,000,000
Research and development expense				200,000	1,200,000	$ 700,000	2,400,000
Date of formation of joint venture entity						Feb. 12, 2016
Equity method investment, ownership percentage		50.00%
Cash contribution		$ 100,000
Other payments due to company from joint venture entity		0
Unrealized equity method losses				1,000,000	1,200,000	$ 2,000,000	2,200,000
Net loss of joint venture				18,100,000	13,500,000	32,300,000	25,800,000
Unrecognized equity method losses in excess of Company's interest						60,500,000		45,300,000
License and Service [Member] | Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue		35,000,000
Royalty [Member] | Casebia Therapeutics LLP [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue		$ 0
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Nonrefundable upfront payment received			$ 75,000,000
Milestone payment receivable			420,000,000
Revenue, remaining performance obligation			82,000,000	57,800,000		57,800,000
Non-current deferred revenue				57,700,000		57,700,000		$ 57,800,000
Research and development expense				6,600,000	200,000	13,700,000	400,000
Reimbursements from research and license agreements				3,300,000	3,700,000	7,800,000	6,900,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | License and Service [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue				$ 100,000	$ 200,000	200,000	$ 400,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Research and Development [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Variable consideration received			19,300,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Joint Development Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Nonrefundable upfront payment received			7,000,000
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 is eligible for a one-time low seven-digit milestone payment upon the dosing of the second patient in a clinical trial with the initial product candidate. The net profits and net losses, as applicable, incurred under the JDA will be shared equally between the Company and Vertex.
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Non-Exclusive Research License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			500,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Material Right to Discounts for Exclusive Licenses [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			57,700,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Unit One [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			22,200,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Unit Two [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			18,700,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Unit Three [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			8,400,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Material Right to Discounts for Exclusive Licenses [Member] | Unit Four [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			8,400,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Co-exclusive Development and Commercialization Licenses and Research License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue, remaining performance obligation			$ 23,800,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Clinical Development And Regulatory Milestone [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of developmental milestone events | Milestone			9
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Clinical Development Milestones [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable			$ 90,000,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Regulatory Approval Milestone [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable			235,000,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Commercial Milestones [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable			$ 75,000,000
Number of developmental milestone events | Milestone			2
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Exercise of Exclusive Option [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable			$ 10,000,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Collaborative Arrangement Copromotion [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payment receivable			10,000,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Commercial Milestone Event One [Member] | Minimum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue			500,000,000
Vertex Pharmaceuticals Incorporated and Certain of its Subsidiaries [Member] | Commercial Milestone Event Two [Member] | Minimum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue			$ 1,000,000,000
[1]	Including the following revenue from a related party, see Notes 6 & 11
[2]	Including the following research and development expense with a related party, see Notes 6 & 11

Share Capital - Additional Info

Share Capital - Additional Information (Detail)	1 Months Ended		3 Months Ended	6 Months Ended
	Jul. 29, 2019USD ($)shares	Aug. 31, 2018USD ($)	Jun. 30, 2019USD ($)shares	Jun. 30, 2019USD ($)shares	Jun. 30, 2018USD ($)	Jun. 30, 2019SFr / shares	Dec. 31, 2018SFr / sharesshares
Class of Stock [Line Items]
Common stock, shares authorized			55,445,241	55,445,241			52,183,139
Common shares, par value | SFr / shares						SFr 0.03	SFr 0.03
Treasury stock, shares			256,989	256,989			307,936
Capital reserved for future issuance			1,683,609	1,683,609
Conditional capital reserved for future issuance			23,948,128	23,948,128			20,498,996
Net cash proceeds from sale of common stock | $				$ 52,294,000	$ 122,597,000
Sales Agreement With Jefferies LLC [Member]
Class of Stock [Line Items]
Common shares sold			732,108	1,363,688
Net cash proceeds from sale of common stock | $			$ 28,500,000	$ 52,500,000
Issuance costs | $			800,000	1,600,000
Payments of stamp taxes related to securities | $			200,000	200,000
Accrued stamp taxes | $			$ 500,000	$ 500,000
Sales Agreement With Jefferies LLC [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Common shares sold	1,124,952
Net cash proceeds from sale of common stock | $	$ 52,800,000
Issuance costs | $	$ 1,200,000
Sales Agreement With Jefferies LLC [Member] | Maximum [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds | $		$ 125,000,000
Swiss Law [Member]
Class of Stock [Line Items]
Common stock, shares authorized			25,134,003	25,134,003
Debt Instruments [Member]
Class of Stock [Line Items]
Conditional capital reserved for future issuance			4,919,700	4,919,700
Unvested Restricted Share Award [Member]
Class of Stock [Line Items]
Unvested restricted stock award			5,586	5,586
Employee Benefit Plans [Member]
Class of Stock [Line Items]
Conditional capital reserved for future issuance			19,028,428	19,028,428

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 12,198	$ 9,477	$ 22,894	$ 16,150
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	5,913	5,167	10,875	8,083
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	5,273	3,157	9,982	5,823
Loss from Equity Method Investment [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,012	$ 1,153	$ 2,037	$ 2,244

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]
Stock Options, Outstanding, Beginning Balance | shares	6,689,311
Stock Options, Granted | shares	1,948,773
Stock Options, Exercised | shares	(263,700)
Stock Options, Cancelled or forfeited | shares	(178,518)
Stock Options, Outstanding, Ending Balance | shares	8,195,866	6,689,311
Stock Options, Exercisable | shares	3,198,255
Stock Options, Vested or expected to vest | shares	8,195,866
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 25.42
Weighted-Average Exercise Price, Granted | $ / shares	36.05
Weighted-Average Exercise Price, Exercised | $ / shares	12.23
Weighted-Average Exercise Price, Cancelled or forfeited | $ / shares	33.48
Weighted-Average Exercise Price, Outstanding, Ending Balance | $ / shares	28.19	$ 25.42
Weighted-Average Exercise Price, Exercisable | $ / shares	19.51
Weighted-Average Exercise Price, Vested or expected to vest | $ / shares	$ 28.19
Weighted-Average Remaining Contractual Term	8 years 3 months 18 days	8 years 3 months 18 days
Weighted-Average Remaining Contractual Term, Exercisable	7 years 6 months
Weighted-Average Remaining Contractual Term, Vested or expected to vest	8 years 3 months 18 days
Aggregate Intrinsic Value, Outstanding Balance | $	$ 167,076	$ 68,572
Aggregate Intrinsic Value, Exercisable | $	91,777
Aggregate Intrinsic Value, Vested or expected to vest | $	$ 167,076

Stock-based Compensation - Assu

Stock-based Compensation - Assumptions to Estimate Fair Value of Stock Option Award Using the Black-Scholes Option-Pricing Model (Detail)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted-average expected volatility	69.30%	72.20%
Expected term (in years)	6 years	6 years
Risk-free interest rate	2.50%	2.70%
Expected dividend yield	0.00%	0.00%

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock options	$ 104,300		$ 104,300
Stock-based compensation expense	12,198	$ 9,477	22,894	$ 16,150
Departing Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 2,200
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 10 months 24 days
Restricted Common Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, remaining weighted-average period for recognition			1 year 4 months 6 days
Total unrecognized compensation expense	$ 8,000		$ 8,000

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Restricted Stock Activity (Detail) - Restricted Stock [Member]	6 Months Ended
	Jun. 30, 2019$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock, Unvested Beginning Balance | shares	327,342
Restricted Stock, Granted | shares	49,000
Restricted Stock, Vested | shares	(24,339)
Restricted Stock, Cancelled or forfeited | shares	(14,000)
Restricted Stock, Unvested Ending Balance | shares	338,003
Weighted-Average Grant Date Fair Value, Unvested Beginning Balance | $ / shares	$ 36.72
Weighted-Average Grant Date Fair Value, Granted | $ / shares	33.30
Weighted-Average Grant Date Fair Value, Vested | $ / shares	14.96
Weighted-Average Grant Date Fair Value, Cancelled or forfeited | $ / shares	38.33
Weighted-Average Grant Date Fair Value, Unvested Ending Balance | $ / shares	$ 37.72

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Shareholders - Schedule of Antidilutive Securities Excluded from Calculation of Net Loss per Share (Detail) - shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of net loss per share	8,533,869	6,787,111
Outstanding Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of net loss per share	8,195,866	6,617,181
Unvested Restricted Common Shares [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of net loss per share	338,003	169,930

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income tax provision	$ 85	$ 96	$ 170	$ 182
Effective income tax rate	(0.20%)	(0.30%)	(0.20%)	(0.30%)

Related Party Transactions - Ad

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

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail)	1 Months Ended
	Jun. 30, 2019USD ($)Option
2019 Collaboration Agreement [Member]
Subsequent Event [Line Items]
Nonrefundable upfront payment received | $	$ 175,000,000
Maximum potential future payments | $	$ 825,000,000
2015 Collaboration Agreement [Member]
Subsequent Event [Line Items]
Number of options would not be exercised under agreement | Option	1
Number of remaining options under agreement | Option	4