Wave Life Sciences (WVE) 10-Q 5 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 01, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Trading Symbol	WVE
Entity Registrant Name	WAVE LIFE SCIENCES LTD.
Entity Incorporation, State or Country Code	U0
Entity Central Index Key	0001631574
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Quarterly Report	true
Document Transition Report	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		34,289,750
Entity Shell Company	false
Entity Tax Identification Number	00-0000000
Entity File Number	001-37627
Entity Address, Address Line One	7 Straits View #12-00
Entity Address, Address Line Two	Marina One East Tower
Entity Address, Country	SG
Entity Address, Postal Zip Code	018936
City Area Code	+65
Local Phone Number	6236 3388
Title of 12(b) Security	$0 Par Value Ordinary Shares
Security Exchange Name	NASDAQ

Unaudited Consolidated Balance

Unaudited Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 209,009	$ 174,819
Current portion of accounts receivable	20,000	10,000
Prepaid expenses and other current assets	21,249	17,454
Total current assets	250,258	202,273
Long-term assets:
Accounts receivable, net of current portion	30,000	50,000
Property and equipment, net	37,204	39,931
Operating lease right-of-use assets	18,527
Restricted cash	3,643	3,625
Other assets	7,580	111
Total long-term assets	96,954	93,667
Total assets	347,212	295,940
Current liabilities:
Accounts payable	20,219	13,089
Accrued expenses and other current liabilities	13,738	14,736
Current portion of deferred rent		115
Current portion of deferred revenue	96,322	100,945
Current portion of lease incentive obligation		1,156
Current portion of operating lease liability	3,132
Total current liabilities	133,411	130,041
Long-term liabilities:
Deferred rent, net of current portion		5,132
Deferred revenue, net of current portion	59,196	68,156
Lease incentive obligation, net of current portion		9,247
Operating lease liability, net of current portion	30,165
Other liabilities	1,793	2,142
Total long-term liabilities	91,154	84,677
Total liabilities	224,565	214,718
Series A preferred shares, no par value; 3,901,348 shares issued and outstanding at September 30, 2019 and December 31, 2018	7,874	7,874
Shareholders’ equity:
Ordinary shares, no par value; 34,284,217 and 29,472,197 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	538,790	375,148
Additional paid-in capital	52,290	37,768
Accumulated other comprehensive income	282	153
Accumulated deficit	(476,589)	(339,721)
Total shareholders’ equity	114,773	73,348
Total liabilities, Series A preferred shares and shareholders’ equity	$ 347,212	$ 295,940

Unaudited Consolidated Balanc_2

Unaudited Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Series A preferred stock, par value	$ 0	$ 0
Series A preferred stock, shares issued	3,901,348	3,901,348
Series A preferred stock, shares outstanding	3,901,348	3,901,348
Common stock, par value	$ 0	$ 0
Common stock, shares issued	34,284,217	29,472,197
Common stock, shares outstanding	34,284,217	29,472,197

Unaudited Consolidated Statemen

Unaudited Consolidated Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 2,929,000	$ 4,493,000	$ 13,583,000	$ 10,794,000
Operating expenses:
Research and development	44,585,000	32,876,000	126,303,000	94,619,000
General and administrative	12,523,000	9,849,000	35,064,000	26,755,000
Total operating expenses	57,108,000	42,725,000	161,367,000	121,374,000
Loss from operations	(54,179,000)	(38,232,000)	(147,784,000)	(110,580,000)
Other income, net:
Dividend income	1,208,000	1,064,000	4,176,000	2,354,000
Interest income, net	6,000	5,000	25,000	16,000
Other income (expense), net	2,239,000	(468,000)	6,715,000	(384,000)
Total other income, net	3,453,000	601,000	10,916,000	1,986,000
Loss before income taxes	(50,726,000)	(37,631,000)	(136,868,000)	(108,594,000)
Income tax provision	0	0	0	(172,000)
Net loss	$ (50,726,000)	$ (37,631,000)	$ (136,868,000)	$ (108,766,000)
Net loss per share attributable to ordinary shareholders—basic and diluted	$ (1.48)	$ (1.28)	$ (4.06)	$ (3.78)
Weighted-average ordinary shares used in computing net loss per share attributable to ordinary shareholders—basic and diluted	34,281,203	29,333,994	33,719,055	28,804,357
Other comprehensive income (loss):
Net loss	$ (50,726,000)	$ (37,631,000)	$ (136,868,000)	$ (108,766,000)
Foreign currency translation	2,000	(20,000)	129,000	65,000
Comprehensive loss	$ (50,724,000)	$ (37,651,000)	$ (136,739,000)	$ (108,701,000)

Unaudited Consolidated Statem_2

Unaudited Consolidated Statements of Series A Preferred Shares and Shareholders' Equity - USD ($) $ in Thousands	Total	Series A Preferred Shares [Member]	Ordinary Shares [Member]	Additional Paid-In-Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2017	$ 139,610		$ 310,038	$ 22,172	$ 116	$ (192,716)
Beginning balance, shares at Dec. 31, 2017			27,829,079
Temporary equity, Beginning balance at Dec. 31, 2017		$ 7,874
Temporary equity, Beginning balance, shares at Dec. 31, 2017		3,901,348
Share-based compensation	4,430			4,430
Vesting of RSUs, shares			38,594
Option exercises	1,553		$ 1,553
Option exercises, shares			125,664
Impact of 2016-16 adoption	(352)					(352)
Other comprehensive income	49				49
Net loss	(35,241)					(35,241)
Ending balance at Mar. 31, 2018	110,049		$ 311,591	26,602	165	(228,309)
Ending balance, shares at Mar. 31, 2018			27,993,337
Temporary equity, Ending balance at Mar. 31, 2018		$ 7,874
Temporary equity, Ending balance, shares at Mar. 31, 2018		3,901,348
Beginning balance at Dec. 31, 2017	139,610		$ 310,038	22,172	116	(192,716)
Beginning balance, shares at Dec. 31, 2017			27,829,079
Temporary equity, Beginning balance at Dec. 31, 2017		$ 7,874
Temporary equity, Beginning balance, shares at Dec. 31, 2017		3,901,348
Net loss	(108,766)
Ending balance at Sep. 30, 2018	106,606		$ 374,502	33,757	181	(301,834)
Ending balance, shares at Sep. 30, 2018			29,426,176
Temporary equity, Ending balance at Sep. 30, 2018		$ 7,874
Temporary equity, Ending balance, shares at Sep. 30, 2018		3,901,348
Beginning balance at Mar. 31, 2018	110,049		$ 311,591	26,602	165	(228,309)
Beginning balance, shares at Mar. 31, 2018			27,993,337
Temporary equity, Beginning balance at Mar. 31, 2018		$ 7,874
Temporary equity, Beginning balance, shares at Mar. 31, 2018		3,901,348
Issuance of ordinary shares	60,000		$ 60,000
Issuance of ordinary shares, shares			1,096,892
Share-based compensation	3,545			3,545
Option exercises	1,560		$ 1,560
Option exercises, shares			203,121
Other comprehensive income	36				36
Net loss	(35,894)					(35,894)
Ending balance at Jun. 30, 2018	139,296		$ 373,151	30,147	201	(264,203)
Ending balance, shares at Jun. 30, 2018			29,293,350
Temporary equity, Ending balance at Jun. 30, 2018		$ 7,874
Temporary equity, Ending balance, shares at Jun. 30, 2018		3,901,348
Share-based compensation	3,610			3,610
Option exercises	1,351		$ 1,351
Option exercises, shares			132,826
Other comprehensive income	(20)				(20)
Net loss	(37,631)					(37,631)
Ending balance at Sep. 30, 2018	106,606		$ 374,502	33,757	181	(301,834)
Ending balance, shares at Sep. 30, 2018			29,426,176
Temporary equity, Ending balance at Sep. 30, 2018		$ 7,874
Temporary equity, Ending balance, shares at Sep. 30, 2018		3,901,348
Beginning balance at Dec. 31, 2018	73,348		$ 375,148	37,768	153	(339,721)
Beginning balance, shares at Dec. 31, 2018			29,472,197
Temporary equity, Beginning balance at Dec. 31, 2018	$ 7,874	$ 7,874
Temporary equity, Beginning balance, shares at Dec. 31, 2018	3,901,348	3,901,348
Issuance of ordinary shares	$ 161,785		$ 161,785
Issuance of ordinary shares, shares			4,542,500
Share-based compensation	4,345			4,345
Vesting of RSUs, shares			110,187
Option exercises	1,481		$ 1,481
Option exercises, shares			130,522
Other comprehensive income	97				97
Net loss	(44,200)					(44,200)
Ending balance at Mar. 31, 2019	196,856		$ 538,414	42,113	250	(383,921)
Ending balance, shares at Mar. 31, 2019			34,255,406
Temporary equity, Ending balance at Mar. 31, 2019		$ 7,874
Temporary equity, Ending balance, shares at Mar. 31, 2019		3,901,348
Beginning balance at Dec. 31, 2018	73,348		$ 375,148	37,768	153	(339,721)
Beginning balance, shares at Dec. 31, 2018			29,472,197
Temporary equity, Beginning balance at Dec. 31, 2018	$ 7,874	$ 7,874
Temporary equity, Beginning balance, shares at Dec. 31, 2018	3,901,348	3,901,348
Net loss	$ (136,868)
Ending balance at Sep. 30, 2019	114,773		$ 538,790	52,290	282	(476,589)
Ending balance, shares at Sep. 30, 2019			34,284,217
Temporary equity, Ending balance at Sep. 30, 2019	$ 7,874	$ 7,874
Temporary equity, Ending balance, shares at Sep. 30, 2019	3,901,348	3,901,348
Beginning balance at Mar. 31, 2019	$ 196,856		$ 538,414	42,113	250	(383,921)
Beginning balance, shares at Mar. 31, 2019			34,255,406
Temporary equity, Beginning balance at Mar. 31, 2019		$ 7,874
Temporary equity, Beginning balance, shares at Mar. 31, 2019		3,901,348
Issuance of ordinary shares	7		$ 7
Share-based compensation	5,157			5,157
Option exercises	116		$ 116
Option exercises, shares			10,854
Other comprehensive income	30				30
Net loss	(41,942)					(41,942)
Ending balance at Jun. 30, 2019	160,224		$ 538,537	47,270	280	(425,863)
Ending balance, shares at Jun. 30, 2019			34,266,260
Temporary equity, Ending balance at Jun. 30, 2019		$ 7,874
Temporary equity, Ending balance, shares at Jun. 30, 2019		3,901,348
Share-based compensation	5,020			5,020
Option exercises	253		$ 253
Option exercises, shares			17,957
Other comprehensive income	2				2
Net loss	(50,726)					(50,726)
Ending balance at Sep. 30, 2019	114,773		$ 538,790	$ 52,290	$ 282	$ (476,589)
Ending balance, shares at Sep. 30, 2019			34,284,217
Temporary equity, Ending balance at Sep. 30, 2019	$ 7,874	$ 7,874
Temporary equity, Ending balance, shares at Sep. 30, 2019	3,901,348	3,901,348

Unaudited Consolidated Statem_3

Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss	$ (136,868)	$ (108,766)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Amortization of lease incentive obligation		(501)
Amortization of right-of-use assets	1,187
Depreciation of property and equipment	5,584	3,867
Share-based compensation expense	14,522	11,585
Net loss on disposal of property and equipment		44
Deferred rent		900
Changes in operating assets and liabilities:
Accounts receivable	10,000	(59,000)
Prepaid expenses and other current assets	(4,422)	(5,687)
Other non-current assets	(7,469)	(15)
Accounts payable	7,471	2,801
Accrued expenses and other current liabilities	(998)	647
Deferred revenue	(13,583)	164,207
Operating lease liabilities	(2,066)
Other non-current liabilities	(349)	(124)
Net cash (used in) provided by operating activities	(126,991)	9,958
Cash flows from investing activities
Purchases of property and equipment	(2,572)	(6,475)
Net cash used in investing activities	(2,572)	(6,475)
Cash flows from financing activities
Proceeds from issuance of ordinary shares, net of offering costs	161,792	60,000
Payments on capital lease obligation		(16)
Proceeds from the exercise of share options	1,850	4,464
Net cash provided by financing activities	163,642	64,448
Effect of foreign exchange rates on cash, cash equivalents and restricted cash	129	65
Net increase in cash, cash equivalents and restricted cash	34,208	67,996
Cash, cash equivalents and restricted cash, beginning of period	178,444	146,113
Cash, cash equivalents and restricted cash, end of period	$ 212,652	$ 214,109

The Company

The Company	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
The Company	1. THE COMPANY Organization Wave Life Sciences Ltd. (together with its subsidiaries, “Wave” or the “Company”) is a clinical-stage genetic medicines company committed to delivering life-changing treatments for people battling devastating diseases. PRISM, Wave’s proprietary discovery and drug development platform, enables Wave to target genetically defined diseases with stereopure oligonucleotides across multiple therapeutic modalities. The Company was incorporated in Singapore on July 23, 2012 and has its principal U.S. office in Cambridge, Massachusetts. The Company was incorporated with the purpose of combining two commonly held companies, Wave Life Sciences USA, Inc. (“Wave USA”), a Delaware corporation (formerly Ontorii, Inc.), and Wave Life Sciences Japan, Inc. (“Wave Japan”), a company organized under the laws of Japan (formerly Chiralgen., Ltd.), which occurred on September 13, 2012. On May 31, 2016, Wave Life Sciences Ireland Limited (“Wave Ireland”) was formed as a wholly - - The Company’s primary activities since inception have been developing PRISM to design, develop and commercialize oligonucleotide therapeutics, advancing the Company’s neurology business, building the Company’s research and development activities in ophthalmology and hepatic, advancing programs into the clinic, furthering clinical development of such clinical-stage programs, building the Company’s intellectual property, and assuring adequate capital to support these activities. Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, developing internal manufacturing capabilities, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. The Company’s therapeutic programs will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization of any product candidates. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities. There can be no assurance that the Company’s research and development efforts will be successful, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. Basis of Presentation The Company has prepared the accompanying consolidated financial statements in conformity with generally accepted accounting principles in the United States (“U.S. GAAP”) and in U.S. dollars.

Significant Accounting Policies

Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Significant Accounting Policies	2. SIGNIFICANT ACCOUNTING POLICIES The significant accounting policies described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018, filed with the Securities and Exchange Commission (“SEC”) on March 1, 2019, as amended (the “2018 Annual Report on Form 10-K”), other than the Company’s adoption of Accounting Standards Codification (“ASC”) Topic 842, Leases (“ASC 842”), which is discussed in detail in Unaudited Interim Financial Data The accompanying interim consolidated balance sheet as of September 30, 2019, the related interim consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2019 and 2018, the consolidated statements of Series A preferred shares and shareholders’ equity for the three months ended March 31, June 30, and September 30, 2019 and 2018, the consolidated statements of cash flows for the nine months ended September 30, 2019 and 2018, and the related interim information contained within the notes to the consolidated financial statements have been prepared in accordance with the rules and regulations of the SEC for interim financial information. Accordingly, they do not include all of the information and the notes required by U.S. GAAP for complete financial statements. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2019 and 2018 are unaudited. In the opinion of management, the unaudited interim consolidated financial statements reflect all adjustments, consisting of normal and recurring adjustments, necessary for the fair presentation of the Company’s financial position and results of operations for the three and nine months ended September 30, 2019 and 2018 . The results of operations for the interim periods are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or any other interim period or future year or period. Principles of Consolidation The Company’s consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Leases Effective January 1, 2019, the Company adopted the new leases standard, ASC 842, using the required modified retrospective approach and utilizing the effective date as its date of initial application, for which prior periods are presented in accordance with the previous guidance in ASC 840, Leases (“ASC 840”). The adoption of this standard resulted in the recognition of operating lease liabilities and right-of-use assets of $35.4 million and $19.7 million, respectively, as well as the derecognition of the deferred rent and lease incentive obligation balances which reduced the right-of-use asset on the Company’s balance sheet as of January 1, 2019 relating to its leases for its corporate headquarters in Cambridge, Massachusetts and for its manufacturing, laboratory and office facility in Lexington, Massachusetts. The adoption of the standard did not have a material effect on the Company’s consolidated statements of operation and comprehensive loss or consolidated statements of cash flows. 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. Most 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 has elected not to recognize on the balance sheet leases with terms of 12 months or less. 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 the lease. The Company monitors its plans to renew its leases on a quarterly basis. Operating lease liabilities and their corresponding right-of-use assets are 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, 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. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rates. In accordance with ASC 842, components of a lease should be split into three categories: lease components (e.g., land, building, etc.), non-lease components (e.g., common area maintenance, consumables, etc.), and non-components (e.g., property taxes, insurance, etc.). The fixed and in-substance fixed contract consideration (including any consideration related to non-components) must be allocated based on the respective relative fair values to the lease components and non-lease components. Although separation of lease and non-lease components is required, certain expedients are available. Entities may elect the practical expedient to not separate lease and non-lease components by class of underlying asset. Rather, entities would account for each lease component and the related non-lease component together as a single component. For new and amended leases beginning in 2019 and after, the Company has elected to account for the lease and non-lease components for leases for classes of all underlying assets and allocate all of the contract consideration to the lease component only. Recently Issued Accounting Pronouncements The recently issued accounting pronouncements described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the 2018 Annual Report on Form 10-K, have had no material changes during the nine months ended September 30, 2019. Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”), which was further clarified when the FASB issued ASU No. 2018-10, Codification Improvements to Topic 842, Leases (“ASU 2018-10”), ASU No. 2018-11, Leases (Topic 842)—Targeted Improvements (“ASU 2018-11”), and ASU No. 2019-01, Codification Improvements to Topic 842, Leases (“ASU 2019-01”). The adoption of ASC 842, in accordance with ASU 2016-02, ASU 2018-10, ASU 2018-11, and ASU 2019-01, requires a lessee to recognize assets and liabilities on the balance sheet for operating leases and change many key definitions, including the definition of a lease. The update includes a short-term lease exception for leases with a term of 12 months or less, in which a lessee can make an accounting policy election not to recognize lease assets and lease liabilities. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases, using classification criteria that are substantially similar to the previous guidance. For lessees, the recognition, measurement, and presentation of expenses and cash flows arising from a lease have not significantly changed from previous U.S. GAAP. Lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The modified retrospective approach includes a number of optional practical expedients that entities may elect to apply, as well as transition guidance specific to nonstandard leasing transactions. As further described above, the Company adopted ASC 842 on January 1, 2019 using a cumulative-effect adjustment on the effective date of the standard, for which comparative periods are presented in accordance with the previous guidance in ASC 840. In adopting ASC 842, the Company elected to utilize the available package of practical expedients permitted under the transition guidance within the new standard, which does not require the reassessment of the following: i) whether existing or expired arrangements are or contain a lease, ii) the lease classification of existing or expired leases, and iii) whether previous initial direct costs would qualify for capitalization under the new lease standard. Additionally, the Company made an accounting policy election to not recognize on the balance sheet leases with a term of 12 months or less. In February 2018, the FASB issued ASU No. 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (“ASU 2018-02”), which allows companies to make a one-time reclassification of the stranded tax effects (as defined by ASU 2018-02) from accumulated other comprehensive income to retained earnings as a result of the tax legislation enacted in December 2017, commonly known as the “Tax Cuts and Jobs Act.” The Company adopted ASU 2018-02 effective as of January 1, 2019 and applied it prospectively. The adoption did not have an impact on the Company’s consolidated financial statements.

January 2019 Follow-On Underwri

January 2019 Follow-On Underwritten Public Offering	9 Months Ended
	Sep. 30, 2019
Follow On Underwritten Public Offering [Abstract]
January 2019 Follow-on Underwritten Public Offering	3. JANUARY 2019 FOLLOW-ON UNDERWRITTEN PUBLIC OFFERING On January 28, 2019, the Company closed a follow-on underwritten public offering of 3,950,000 ordinary shares for gross proceeds of $150.1 million, and on February 26, 2019, the Company closed on the sale of an additional 592,500 ordinary shares pursuant to the underwriters’ option (on the same terms and conditions as the initial closing) for gross proceeds of an additional $22.5 million (collectively, the “January 2019 Offering”). The net proceeds to the Company from the January 2019 Offering were $161.8 million, after deducting underwriting discounts and commissions and offering expenses.

Share-Based Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-Based Compensation	4 . SHARE-BASED COMPENSATION The Wave Life Sciences Ltd. 2014 Equity Incentive Plan, as amended (the “2014 Plan”), authorizes the board of directors or a committee of the board of directors to, among other things, grant non-qualified share options, restricted awards, which includes restricted shares and time-based and performance-based restricted share units (“RSUs”) to eligible employees and directors of the Company. Options generally vest over periods of one to four years, and any options that are forfeited or cancelled are available to be granted again. The contractual life of options is generally five or ten years from the grant date. RSUs are either time-based or performance-based. Time-based RSUs generally vest over a period of one or four years. Performance-based RSUs vest upon the achievement of certain milestones. Any RSUs that are forfeited are available to be granted again. During the nine months ended September 30, 2019, the Company granted 163,200 options to employees and non-employee directors and 1,542,780 RSUs to employees. Of the RSUs granted, 543,840 were time-based RSUs and 998,940 were performance-based RSUs. Vesting of these performance-based RSUs is contingent on the occurrence of certain regulatory and commercial milestones. As of September 30, 2019, 1,081,569 ordinary shares remained available for future grant under the 2014 Plan.

Collaboration Agreements

Collaboration Agreements	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration Agreements	5. COLLABORATION AGREEMENTS Pfizer Collaboration and Equity Agreements In May 2016, the Company entered into a Research, License and Option Agreement (as amended in November 2017, the “Pfizer Collaboration Agreement”) with Pfizer Inc. (“Pfizer”). Pursuant to the terms of the Pfizer Collaboration Agreement, the Company and Pfizer agreed to collaborate on the discovery, development and commercialization of stereopure oligonucleotide therapeutics for up to five programs (the “Pfizer Programs”), each directed at a genetically-defined hepatic target selected by Pfizer (the “Pfizer Collaboration”). The Company received $10.0 million as an upfront license fee under the Pfizer Collaboration Agreement. Subject to option exercises by Pfizer, the Company may earn potential research, development and commercial milestone payments, plus royalties, tiered up to low double-digits, on sales of any products that may result from the Pfizer Collaboration. None of the payments under the Pfizer Collaboration Agreement are refundable. Simultaneously with the entry into the Pfizer Collaboration Agreement, the Company entered into a Share Purchase Agreement (the “Pfizer Equity Agreement,” and together with the Pfizer Collaboration Agreement, the “Pfizer Agreements”) with C.P. Pharmaceuticals International C.V., an affiliate of Pfizer (the “Pfizer Affiliate”). Pursuant to the terms of the Pfizer Equity Agreement, the Pfizer Affiliate purchased 1,875,000 of the Company’s ordinary shares (the “Shares”) at a purchase price of $16.00 per share, for an aggregate purchase price of $30.0 million. The Company did not incur any material costs in connection with the issuance of the Shares. Under the Pfizer Collaboration Agreement, the parties agreed to collaborate during a four-year research term. During the research term, the Company is responsible to use its commercially reasonable efforts to advance up to five programs through to the selection of clinical candidates. At that stage, Pfizer may elect to license any of these Pfizer Programs exclusively and obtain exclusive rights to undertake the clinical development of the resulting clinical candidates into products and the potential commercialization of any such products thereafter. In addition, the Company received a non-exclusive, royalty-bearing sublicensable license to use Pfizer’s hepatic targeting technology in any of the Company’s own hepatic programs that are outside the scope of the Pfizer Collaboration (the “Wave Programs”). If the Company uses this technology on the Wave Programs, Pfizer is eligible to receive potential development and commercial milestone payments from the Company. Pfizer is also eligible to receive tiered royalties on sales of any products that include Pfizer’s hepatic targeting technology. The stated term of the Pfizer Collaboration Agreement commenced on May 5, 2016 and terminates on the date of the last to expire payment obligation with respect to each Pfizer Program and, with respect to each Wave Program, expires on a program-by-program basis accordingly. Pfizer may terminate its rights related to a Pfizer Program under the Pfizer Collaboration Agreement at its own convenience upon 90 days’ notice to the Company. The Company may also terminate its rights related to a Wave Program at its own convenience upon 90 days’ notice to Pfizer. The Pfizer Collaboration Agreement may also be terminated by either party in the event of an uncured material breach of the Pfizer Collaboration Agreement by the other party. Pfizer nominated two hepatic targets upon entry into the Pfizer Collaboration in May 2016. The Pfizer Collaboration Agreement provides Pfizer with options to nominate up to three additional programs by making nomination milestone payments. Pfizer nominated the third, fourth and fifth hepatic targets in August 2016, March 2018 and April 2018, respectively. The Pfizer Collaboration is managed by a joint steering committee in which both parties are represented equally, which will oversee the scientific progression of each Pfizer Program up to the clinical candidate stage. During the four-year research term and for a period of two years thereafter, the Company has agreed to work exclusively with Pfizer with respect to using any of the Company’s stereopure oligonucleotide technology that is specific for the applicable hepatic target which is the basis of any Pfizer Program. Within a specified period after receiving a data package for a candidate under each nominated program, Pfizer may exercise an option to obtain a license to develop, manufacture and commercialize the program candidate by paying an exercise price per program. The Company assessed this arrangement in accordance with ASC 606 and concluded that the contract counterparty, Pfizer, is a customer. The Company identified the following promises under the arrangement: (1) the non-exclusive, royalty-free research and development license; (2) the research and development services for Programs 1 and 2; (3) the program nomination options for Programs 3, 4 and 5; (4) the research and development services associated with Programs 3, 4 and 5; (5) the options to obtain a license to develop, manufacture and commercialize Programs 1 and 2; and (6) the options to obtain a license to develop, manufacture and commercialize Programs 3, 4 and 5. The research and development services for each of Programs 1 and 2 were determined to not be distinct from the research and development license and should be combined into a single performance obligation for each program. The promises under the Pfizer Collaboration Agreement relate primarily to the research and development required by the Company for each of the programs nominated by Pfizer. Additionally, the Company determined that the program nomination options for Programs 3, 4 and 5 were priced at a discount and, as such, provide material rights to Pfizer, representing three separate performance obligations. The research and development services associated with Programs 3, 4 and 5 and the options to obtain a license to develop, manufacture and commercialize Programs 3, 4 and 5 are subject to Pfizer’s exercise of the program nomination options for such programs and therefore do not represent performance obligations at the outset of the arrangement. The options to obtain a license to develop, manufacture and commercialize Programs 1 and 2 do not represent material rights; as such, they are not representative of performance obligations at the outset of the arrangement. Based on these assessments, the Company identified five performance obligations in the Pfizer Collaboration Agreement: (1) research and development services and license for Program 1; (2) research and development services and license for Program 2; (3) material right provided for the option to nominate Program 3; (4) material right provided for the option to nominate Program 4; and (5) material right provided for the option to nominate Program 5. At the outset of the arrangement, the transaction price included only the $10.0 million up-front consideration received. The Company determined that the Pfizer Collaboration Agreement did not contain a significant financing component. The program nomination option exercise fees for research and development services associated with Programs 3, 4 and 5 that may be received are excluded from the transaction price until each customer option is exercised. The potential milestone payments were excluded from the transaction price, as all milestone amounts were fully constrained at the inception of the Pfizer Collaboration Agreement. The exercise fees for the options to obtain a license to develop, manufacture and commercialize Programs 3, 4 and 5 that may be received are excluded from the transaction price until each customer option is exercised. The Company will reevaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, will adjust its estimate of the transaction price. During the year ended December 31, 2017 , it became probable that a significant reversal of cumulative revenue would not occur for a developmental milestone under the Pfizer Collaboration Agreement. At such time, the associated consideration was added to the estimated transaction price and allocated to the existing performance obligations, and the Company recognized a cumulative catch-up to revenue for this developmental milestone, representing the amount that would have been recognized had the milestone payment been included in the transaction price from the outset of the arrangement. The remainder will be recognized in the same manner as the remaining, unrecognized transaction price over the remaining period until each performance obligation is satisfied. Revenue associated with the performance obligations relating to Programs 1 and 2 is being recognized as revenue as the research and development services are provided using an input method, according to the full-time employee (“FTE”) hours incurred on each program and the FTE hours expected to be incurred in the future to satisfy the performance obligation. The transfer of control occurs over time and, in management’s judgment, this input method is the best measure of progress towards satisfying the performance obligation. The amount allocated to the three material rights will be recognized as the underlying research and development services are provided commencing from the date that Pfizer exercises each respective option, or immediately as each option expires unexercised. The amounts received that have not yet been recognized as revenue are recorded in deferred revenue on the Company’s consolidated balance sheet. Pfizer nominated the third, fourth and fifth hepatic targets in August 2016, March 2018 and April 2018, respectively. Upon each exercise, the Company allocated the transaction price amount allocated to the material right at inception of the arrangement plus the program nomination option exercise fee paid by Pfizer at the time of exercising the option to a new performance obligation, which will be recognized as revenue as the research and development services are provided using the same method as the performance obligations relating to Programs 1 and 2. Through September 30, 2019, the Company had recognized revenue of $15.8 million as collaboration revenue in the Company’s consolidated statements of operations and comprehensive loss under the Pfizer Collaboration Agreement. During the three and nine months ended September 30, 2019, the Company recognized revenue of $1.3 million and $6.0 million, respectively, under the Pfizer Collaboration Agreement. During the three and nine months ended September 30, 2018, the Company recognized revenue of $1.0 million and $3.9 million, respectively, under the Pfizer Collaboration Agreement. The aggregate amount of the transaction price allocated to the Company’s partially unsatisfied performance obligations and recorded in deferred revenue at September 30, 2019 is $2.7 million, all of which is included in current liabilities. The Company expects to recognize this amount according to FTE hours incurred, over the remaining research term, which is seven months as of September 30, 2019. Takeda Collaboration and Equity Agreements In February 2018, Wave USA and Wave UK entered into a global strategic collaboration (the “Takeda Collaboration”) with Takeda Pharmaceutical Company Limited (“Takeda”), pursuant to which Wave USA, Wave UK and Takeda agreed to collaborate on the research, development and commercialization of oligonucleotide therapeutics for disorders of the Central Nervous System (“CNS”). The Takeda Collaboration provides Wave with at least $230.0 million in committed cash and Takeda with the option to co-develop and co-commercialize Wave’s CNS development programs in (1) Huntington’s disease (“HD”); (2) amyotrophic lateral sclerosis (“ALS”) and frontotemporal dementia (“FTD”); and (3) Wave’s discovery-stage program targeting ATXN3 Simultaneously with Wave USA and Wave UK’s entry into the collaboration and license agreement with Takeda (the “Takeda Collaboration Agreement”), the Company entered into a share purchase agreement with Takeda (the “Takeda Equity Agreement,” and together with the Takeda Collaboration Agreement, the “Takeda Agreements”) pursuant to which it agreed to sell to Takeda 1,096,892 of its ordinary shares at a purchase price of $54.70 per share. In April 2018, the Company closed the Takeda Equity Agreement and received aggregate cash proceeds of $60.0 million. The Company did not incur any material costs in connection with the issuance of shares. With respect to Category 1 Programs, Wave will be responsible for researching and developing products and companion diagnostics for Category 1 Programs through completion of the first proof of mechanism study for such products. Takeda will have an exclusive option for each target and all associated products and companion diagnostics for such target, which it may exercise at any time through completion of the proof of mechanism study. If Takeda exercises this option, Wave will receive an opt-in payment and will lead manufacturing and joint clinical co-development activities and Takeda will lead joint co-commercial activities in the United States and all commercial activities outside of the United States. Global costs and potential profits will be shared 50:50 and Wave will be eligible to receive development and commercial milestone payments. In addition to its 50% profit share, Wave is eligible to receive option exercise fees and development and commercial milestone payments for each of the Category 1 Programs. With respect to Category 2 Programs, Wave has granted Takeda the right to exclusively license multiple preclinical programs during a four-year research term (subject to limited extension for programs that were initiated prior to the expiration of the research term, in accordance with the Takeda Collaboration Agreement) (“Category 2 Research Term”). During that term, the parties may collaborate on preclinical programs for up to six targets at any one time. Wave will be responsible for researching and preclinically developing products and companion diagnostics directed to the agreed upon targets through completion of Investigational New Drug application (“IND“)-enabling studies in the first major market country. Thereafter, Takeda will have an exclusive worldwide license to develop and commercialize products and companion diagnostics directed to such targets, subject to Wave’s retained rights to lead manufacturing activities for products directed to such targets. Takeda will fund Wave’s research and preclinical activities in the amount of $60.0 million during the research term and will reimburse Wave for any collaboration-budgeted research and preclinical expenses incurred by Wave that exceed that amount. Wave is also eligible to receive tiered high single-digit to mid-teen royalties on Takeda’s global commercial sales of products from each Category 2 Program. Under the Takeda Collaboration Agreement, each party grants to the other party specific intellectual property licenses to enable the other party to perform its obligations and exercise its rights under the Takeda Collaboration Agreement, including license grants to enable each party to conduct research, development and commercialization activities pursuant to the terms of the Takeda Collaboration Agreement. The term of the Takeda Collaboration Agreement commenced on April 2, 2018 and, unless terminated earlier, will continue until the date on which: (i) with respect to each Category 1 Program target for which Takeda does not exercise its option, the expiration or termination of the development program with respect to such target; (ii) with respect to each Category 1 Program target for which Takeda exercises its option, the date on which neither party is researching, developing or manufacturing any products or companion diagnostics directed to such target; or (iii) with respect to each Category 2 Program target, the date on which royalties are no longer payable with respect to products directed to such target. Takeda may terminate the Takeda Collaboration Agreement for convenience on 180 days’ notice, in its entirety or on a target-by-target basis. Subject to certain exceptions, each party has the right to terminate the Takeda Collaboration Agreement on a target-by-target basis if the other party, or a third party related to such party, challenges the patentability, enforceability or validity of any patents within the licensed technology that cover any product or companion diagnostic that is subject to the Takeda Collaboration Agreement. In the event of any material breach of the Takeda Collaboration Agreement by a party, subject to cure rights, the other party may terminate the Takeda Collaboration Agreement in its entirety if the breach relates to all targets or on a target-by-target basis if the breach relates to a specific target. In the event that Takeda and its affiliates cease development, manufacturing and commercialization activities with respect to compounds or products subject to the Takeda Collaboration Agreement and directed to a particular target, Wave may terminate the Takeda Collaboration Agreement with respect to such target. Either party may terminate the Takeda Collaboration Agreement for the other party’s insolvency. In certain termination circumstances, Wave would receive a license from Takeda to continue researching, developing and manufacturing certain products, and companion diagnostics. The Company assessed this arrangement in accordance with ASC 606 and concluded that the contract counterparty, Takeda, is a customer for Category 1 Programs prior to Takeda exercising its option, and for Category 2 Programs during the Category 2 Research Term. The Company identified the following material promises under the arrangement: (1) the non-exclusive, royalty-free research and development license for each Category 1 Program; (2) the research and development services for each Category 1 Program through completion of the first proof of mechanism study; (3) the exclusive option to license, co-develop and co-commercialize each Category 1 Program; (4) the right to exclusively license the Category 2 Programs; and (5) the research and preclinical development services of the Category 2 Programs through completion of IND-enabling studies. The research and development services for each Category 1 Program were determined to not be distinct from the research and development license and should therefore be combined into a single performance obligation for each Category 1 Program. The research and preclinical development services for the Category 2 Programs were determined to not be distinct from the exclusive licenses for the Category 2 Programs and should therefore be combined into a single performance obligation. Additionally, the Company determined that the exclusive option for each Category 1 Program was priced at a discount, and, as such, provide material rights to Takeda, representing three separate performance obligations. Based on these assessments, the Company identified seven performance obligations in the Takeda Collaboration Agreement: (1) research and development services through completion of the first proof of mechanism and non-exclusive research and development license for HD; (2) research and development services through completion of the first proof of mechanism and non-exclusive research and development license for ALS and FTD; (3) research and development services through completion of the first proof of mechanism and non-exclusive research and development license for SCA3; (4) the material right provided for the exclusive option to license, co-develop and co-commercialize HD; (5) the material right provided for the exclusive option to license, co-develop and co-commercialize ALS and FTD; (6) the material right provided for the exclusive option to license, co-develop and co-commercialize SCA3; and (7) the research and preclinical development services and right to exclusively license the Category 2 Programs. At the outset of the arrangement, the transaction price included the $110.0 million upfront consideration received and the $60.0 million of committed research and preclinical funding for the Category 2 Programs. The Company determined that the Takeda Collaboration Agreement did not contain a significant financing component. The option exercise fees to license, co-develop and co-commercialize each Category 1 Program that may be received are excluded from the transaction price until each customer option is exercised. The potential milestone payments were excluded from the transaction price, as all milestone amounts were fully constrained at the inception of the Takeda Collaboration Agreement. The Company will reevaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, if necessary, will adjust its estimate of the transaction price. Revenue associated with the research and development services for each Category 1 Program performance obligation is being recognized as the research and development services are provided using an input method, according to the costs incurred on each Category 1 Program and the total costs expected to be incurred to satisfy each Category 1 Program performance obligation. Revenue associated with the research and preclinical development services for the Category 2 Programs performance obligation is being recognized as the research and preclinical development services are provided using an input method, according to the costs incurred on Category 2 Programs and the total costs expected to be incurred to satisfy the performance obligation. The transfer of control for these performance obligations occurs over time and, in management’s judgment, this input method is the best measure of progress towards satisfying the performance obligations. The amount allocated to the material right for each Category 1 Program option will be recognized on the date that Takeda exercises each respective option, or immediately as each option expires unexercised. The amounts received that have not yet been recognized as revenue are recorded in deferred revenue on the Company’s consolidated balance sheet. Through September 30, 2019, the Company had recognized revenue of $17.2 million as collaboration revenue in the Company’s consolidated statements of operations and comprehensive loss under the Takeda Collaboration Agreement. During the three and nine months ended September 30, 2019, the Company recognized revenue of $1.6 million and $7.6 million, respectively, in the Company’s consolidated statements of operations and comprehensive loss under the Takeda Collaboration Agreement. During the three and nine months ended September 30, 2018, the Company recognized revenue of $3.5 million and $6.9 million, respectively, in the Company’s consolidated statements of operations and comprehensive loss under the Takeda Collaboration Agreement. The aggregate amount of the transaction price allocated to the Company’s unsatisfied and partially unsatisfied performance obligations and recorded in deferred revenue at September 30, 2019 is $152.8 million, of which $93.6 million is included in current liabilities. The Company expects to recognize revenue for the portion of the deferred revenue that relates to the research and development services for each Category 1 Program and the Category 2 Programs as costs are incurred, over the remaining research term. The Company expects to recognize revenue for the portion of the deferred revenue that relates to the material right for each Category 1 Program option upon Takeda’s exercise of such option, or immediately as each option expires unexercised. The aggregate amount of the transaction price included in accounts receivable at September 30, 2019 is $50.0 million, of which $20.0 million is included in current assets.

Net Loss Per Ordinary Share

Net Loss Per Ordinary Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Loss Per Ordinary Share	6. NET LOSS PER ORDINARY SHARE The Company applies the two-class method to calculate its basic and diluted net loss per share attributable to ordinary shareholders, as its Series A preferred shares are participating securities. The two-class method is an earnings allocation formula that treats a participating security as having rights to earnings that otherwise would have been available to ordinary shareholders. Basic loss per share is computed by dividing net loss attributable to ordinary shareholders by the weighted-average number of ordinary shares. The Company’s potentially dilutive shares, which include outstanding share options to purchase ordinary shares, RSUs and Series A preferred shares, are considered to be ordinary share equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. The following ordinary share equivalents, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to ordinary shareholders for the periods indicated because including them would have had an anti-dilutive effect: As of September 30, 2019 2018 Options to purchase ordinary shares 3,902,994 3,912,336 RSUs 1,744,177 408,534 Series A preferred shares 3,901,348 3,901,348 Additionally, for the periods presented, the two-class method does not impact the net loss per ordinary share as the Company was in a net loss position for each of the periods presented and holders of Series A preferred shares d o not participate in losses.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	7. INCOME TAXES During the three months ended September 30, 2019 and 2018, the Company recorded no income tax provision . During the nine months ended September 30, 2019 and 2018, the Company recorded no income tax provision and an income tax provision of $0.2 million, respectively. The income tax provision recorded during the nine months ended September 30, 2018 was due to return-to-provision adjustments related to the filing of Wave Japan’s 2017 tax return . The Company maintained a full valuation allowance for the three and nine months ended September 30, 2019 and 2018 in all jurisdictions due to uncertainty regarding future taxable income. The Company’s reserves related to taxes and its accounting for uncertain tax positions are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is more-likely-than-not to be realized following resolution of any potential contingencies present related to the tax benefit.

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases	8. LEASES The Company enters into lease arrangements for its facilities. A summary of the arrangements is as follows: Operating Leases On September 26, 2016, and as amended on December 31, 2016, the Company entered into a 10 year and 9 month lease, which includes two successive five year renewal options, for its facility in Lexington, Massachusetts, which the Company uses primarily for its current good manufacturing practices (“cGMP”) manufacturing, as well as for additional laboratory and office space. Throughout the term of the lease, the Company is responsible for paying certain costs and expenses, in addition to the rent, as specified in the lease, including a proportionate share of applicable taxes, operating expenses and utilities. As required under the terms of the lease agreement, the Company has placed restricted cash of $2.6 million in a separate bank account at September 30, 2019 and December 31, 2018. As of December 31, 2018, the Company has received the $11.4 million of tenant improvement allowances to which it was entitled under the lease for the Lexington, Massachusetts facility. In applying the ASC 842 transition guidance, the Company utilized the operating classification and recorded a lease liability and a right-of-use asset on the ASC 842 effective date, with the lease incentive obligation being de-recognized and serving to reduce the right-of-use asset. In April 2015, the Company entered into a lease agreement for an office and laboratory facility in Cambridge, Massachusetts, which commenced in October 2015 with a term of 7.5 years and a five-year renewal option to extend the lease. As required under the terms of the lease agreement, the Company has placed restricted cash of $1.0 million in a separate bank account at September 30, 2019 and December 31, 2018. In applying the ASC 842 transition guidance, the Company classified this lease as an operating lease and recorded a right-of-use asset and lease liability on the effective date. The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the nine months ended September 30, 2019: For the Nine Months Ended September 30, 2019 (in thousands) Lease cost Operating lease cost $ 3,354 Total lease cost $ 3,354 Other information Operating cash flows used for operating leases $ 4,233 Operating lease liabilities arising from obtaining right-of-use assets $ — Weighted average remaining lease term 7.5 years Weighted average discount rate 8.5 % Future minimum lease payments under the Company’s non-cancelable operating leases as of September 30, 2019, are as follows: As of September 30, 2019 (in thousands) 2019 $ 1,442 2020 5,846 2021 6,021 2022 6,201 2023 5,236 Thereafter 20,927 Total lease payments $ 45,673 Less: imputed interest (12,376 ) Total operating lease liabilities $ 33,297

Geographic Data

Geographic Data	9 Months Ended
	Sep. 30, 2019
Geographic Data [Abstract]
Geographic Data	9. GEOGRAPHIC DATA Substantially all of the Company’s long-lived assets were located in the United States as of September 30, 2019 and December 31, 2018.

Related Parties

Related Parties	9 Months Ended
	Sep. 30, 2019
Related Party Transactions [Abstract]
Related Parties	10. RELATED PARTIES The Company had the following related party transaction for the periods presented in the accompanying consolidated financial statements, which has not otherwise been discussed in these notes to the consolidated financial statements: • In 2012, the Company entered into a consulting agreement for scientific advisory services with Dr. Gregory L. Verdine, one of the Company’s founders and a member of the Company’s board of directors. The consulting agreement does not have a specific term and may be terminated by either party upon 14 days

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Unaudited Interim Financial Data	Unaudited Interim Financial Data The accompanying interim consolidated balance sheet as of September 30, 2019, the related interim consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2019 and 2018, the consolidated statements of Series A preferred shares and shareholders’ equity for the three months ended March 31, June 30, and September 30, 2019 and 2018, the consolidated statements of cash flows for the nine months ended September 30, 2019 and 2018, and the related interim information contained within the notes to the consolidated financial statements have been prepared in accordance with the rules and regulations of the SEC for interim financial information. Accordingly, they do not include all of the information and the notes required by U.S. GAAP for complete financial statements. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2019 and 2018 are unaudited. In the opinion of management, the unaudited interim consolidated financial statements reflect all adjustments, consisting of normal and recurring adjustments, necessary for the fair presentation of the Company’s financial position and results of operations for the three and nine months ended September 30, 2019 and 2018 . The results of operations for the interim periods are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or any other interim period or future year or period.
Principles of Consolidation	Principles of Consolidation The Company’s consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Leases	Leases Effective January 1, 2019, the Company adopted the new leases standard, ASC 842, using the required modified retrospective approach and utilizing the effective date as its date of initial application, for which prior periods are presented in accordance with the previous guidance in ASC 840, Leases (“ASC 840”). The adoption of this standard resulted in the recognition of operating lease liabilities and right-of-use assets of $35.4 million and $19.7 million, respectively, as well as the derecognition of the deferred rent and lease incentive obligation balances which reduced the right-of-use asset on the Company’s balance sheet as of January 1, 2019 relating to its leases for its corporate headquarters in Cambridge, Massachusetts and for its manufacturing, laboratory and office facility in Lexington, Massachusetts. The adoption of the standard did not have a material effect on the Company’s consolidated statements of operation and comprehensive loss or consolidated statements of cash flows. 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. Most 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 has elected not to recognize on the balance sheet leases with terms of 12 months or less. 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 the lease. The Company monitors its plans to renew its leases on a quarterly basis. Operating lease liabilities and their corresponding right-of-use assets are 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, 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. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rates. In accordance with ASC 842, components of a lease should be split into three categories: lease components (e.g., land, building, etc.), non-lease components (e.g., common area maintenance, consumables, etc.), and non-components (e.g., property taxes, insurance, etc.). The fixed and in-substance fixed contract consideration (including any consideration related to non-components) must be allocated based on the respective relative fair values to the lease components and non-lease components. Although separation of lease and non-lease components is required, certain expedients are available. Entities may elect the practical expedient to not separate lease and non-lease components by class of underlying asset. Rather, entities would account for each lease component and the related non-lease component together as a single component. For new and amended leases beginning in 2019 and after, the Company has elected to account for the lease and non-lease components for leases for classes of all underlying assets and allocate all of the contract consideration to the lease component only.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements The recently issued accounting pronouncements described in the Company’s audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the 2018 Annual Report on Form 10-K, have had no material changes during the nine months ended September 30, 2019. Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”), which was further clarified when the FASB issued ASU No. 2018-10, Codification Improvements to Topic 842, Leases (“ASU 2018-10”), ASU No. 2018-11, Leases (Topic 842)—Targeted Improvements (“ASU 2018-11”), and ASU No. 2019-01, Codification Improvements to Topic 842, Leases (“ASU 2019-01”). The adoption of ASC 842, in accordance with ASU 2016-02, ASU 2018-10, ASU 2018-11, and ASU 2019-01, requires a lessee to recognize assets and liabilities on the balance sheet for operating leases and change many key definitions, including the definition of a lease. The update includes a short-term lease exception for leases with a term of 12 months or less, in which a lessee can make an accounting policy election not to recognize lease assets and lease liabilities. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases, using classification criteria that are substantially similar to the previous guidance. For lessees, the recognition, measurement, and presentation of expenses and cash flows arising from a lease have not significantly changed from previous U.S. GAAP. Lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The modified retrospective approach includes a number of optional practical expedients that entities may elect to apply, as well as transition guidance specific to nonstandard leasing transactions. As further described above, the Company adopted ASC 842 on January 1, 2019 using a cumulative-effect adjustment on the effective date of the standard, for which comparative periods are presented in accordance with the previous guidance in ASC 840. In adopting ASC 842, the Company elected to utilize the available package of practical expedients permitted under the transition guidance within the new standard, which does not require the reassessment of the following: i) whether existing or expired arrangements are or contain a lease, ii) the lease classification of existing or expired leases, and iii) whether previous initial direct costs would qualify for capitalization under the new lease standard. Additionally, the Company made an accounting policy election to not recognize on the balance sheet leases with a term of 12 months or less. In February 2018, the FASB issued ASU No. 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (“ASU 2018-02”), which allows companies to make a one-time reclassification of the stranded tax effects (as defined by ASU 2018-02) from accumulated other comprehensive income to retained earnings as a result of the tax legislation enacted in December 2017, commonly known as the “Tax Cuts and Jobs Act.” The Company adopted ASU 2018-02 effective as of January 1, 2019 and applied it prospectively. The adoption did not have an impact on the Company’s consolidated financial statements.

Net Loss Per Ordinary Share (Ta

Net Loss Per Ordinary Share (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Anti-Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Ordinary Share	The following ordinary share equivalents, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to ordinary shareholders for the periods indicated because including them would have had an anti-dilutive effect: As of September 30, 2019 2018 Options to purchase ordinary shares 3,902,994 3,912,336 RSUs 1,744,177 408,534 Series A preferred shares 3,901,348 3,901,348

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Schedule of Lease Costs Recognized and Other Information Pertaining to Operating Leases	The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the nine months ended September 30, 2019: For the Nine Months Ended September 30, 2019 (in thousands) Lease cost Operating lease cost $ 3,354 Total lease cost $ 3,354 Other information Operating cash flows used for operating leases $ 4,233 Operating lease liabilities arising from obtaining right-of-use assets $ — Weighted average remaining lease term 7.5 years Weighted average discount rate 8.5 %
Schedule of Future Minimum Rental Payments for Operating Leases Under Topic 842	Future minimum lease payments under the Company’s non-cancelable operating leases as of September 30, 2019, are as follows: As of September 30, 2019 (in thousands) 2019 $ 1,442 2020 5,846 2021 6,021 2022 6,201 2023 5,236 Thereafter 20,927 Total lease payments $ 45,673 Less: imputed interest (12,376 ) Total operating lease liabilities $ 33,297

Significant Accounting Polici_3

Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019
Accounting Policies [Abstract]
Operating lease, liability	$ 33,297	$ 35,400
Operating lease, right-of-use asset	$ 18,527	$ 19,700

January 2019 Follow-On Underw_2

January 2019 Follow-On Underwritten Public Offering - Additional Information (Detail) - USD ($) $ in Thousands	Feb. 26, 2019	Jan. 28, 2019	Feb. 26, 2019	Sep. 30, 2019	Sep. 30, 2018
Follow On Underwritten Public Offering [Line Items]
Net proceeds from sale of ordinary shares				$ 161,792	$ 60,000
Follow-On Underwritten Public Offering [Member]
Follow On Underwritten Public Offering [Line Items]
Shares issued under equity agreement	592,500	3,950,000
Gross proceeds from sale of ordinary shares	$ 22,500	$ 150,100
Net proceeds from sale of ordinary shares			$ 161,800

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2019shares
Time-based RSUs [Member]
Share-based Compensation Arrangement By Share-based Payment Award [Line Items]
Shares granted to employees	543,840
Performance Based RSUs [Member]
Share-based Compensation Arrangement By Share-based Payment Award [Line Items]
Shares granted to employees	998,940
Options [Member]
Share-based Compensation Arrangement By Share-based Payment Award [Line Items]
Options granted to employees and non-employee directors	163,200
RSUs to Employees [Member}
Share-based Compensation Arrangement By Share-based Payment Award [Line Items]
Shares granted to employees	1,542,780
2014 Plan [Member]
Share-based Compensation Arrangement By Share-based Payment Award [Line Items]
Ordinary shares available for future grant	1,081,569
2014 Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement By Share-based Payment Award [Line Items]
Vesting period	1 year
Contractual life of options	5 years
2014 Plan [Member] | Minimum [Member] | Time-based RSUs [Member]
Share-based Compensation Arrangement By Share-based Payment Award [Line Items]
Vesting period	1 year
2014 Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement By Share-based Payment Award [Line Items]
Vesting period	4 years
Contractual life of options	10 years
2014 Plan [Member] | Maximum [Member] | Time-based RSUs [Member]
Share-based Compensation Arrangement By Share-based Payment Award [Line Items]
Vesting period	4 years

Collaboration Agreements - Addi

Collaboration Agreements - Additional Information (Detail)	Apr. 02, 2018	May 05, 2016USD ($)	Apr. 30, 2018USD ($)Target$ / sharesshares	Feb. 28, 2018USD ($)	May 31, 2016USD ($)Program$ / sharesshares	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Equity investment aggregate purchase price							$ 7,000	$ 161,785,000		$ 60,000,000
Proceeds from issuance of ordinary shares, net of offering costs											$ 161,792,000	$ 60,000,000
Collaboration revenue recognized						$ 2,929,000			$ 4,493,000		13,583,000	10,794,000
Collaboration and license agreement, deferred revenue current						96,322,000					$ 96,322,000		$ 96,322,000	$ 96,322,000	$ 100,945,000
Pfizer Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of research programs, counterparty nomination | Program					5
Research term, description											Under the Pfizer Collaboration Agreement, the parties agreed to collaborate during a four-year research term. During the research term, the Company is responsible to use its commercially reasonable efforts to advance up to five programs through to the selection of clinical candidates. At that stage, Pfizer may elect to license any of these Pfizer Programs exclusively and obtain exclusive rights to undertake the clinical development of the resulting clinical candidates into products and the potential commercialization of any such products thereafter.
Collaboration agreement, additional period after research program		2 years
Up-front consideration received		$ 10,000,000
Revenue recognized						1,300,000			1,000,000		$ 6,000,000	3,900,000		15,800,000
Collaboration and license agreement, deferred revenue						2,700,000					$ 2,700,000		2,700,000	2,700,000
Remaining research term											7 months
Takeda [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front consideration received			$ 110,000,000
Research, License and Option Agreement [Member] | Pfizer Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment under collaboration agreement					$ 10,000,000
Collaboration agreement refundable					$ 0
Shares issued under equity agreement | shares					1,875,000
Equity investment aggregate purchase price					$ 30,000,000
Purchase price per share | $ / shares					$ 16
Collaborative agreement research term					4 years
Collaboration agreement termination period		90 days
Collaboration And License Agreement [Member] | Category One Programs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of global costs and potential profits sharing ratio			50.00%
Collaboration And License Agreement [Member] | Takeda [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment under collaboration agreement			$ 110,000,000
Collaboration agreement termination period	180 days
Collaboration and license agreement, deferred revenue						152,800,000					$ 152,800,000		152,800,000	152,800,000
Collaboration and license agreement month and year			2018-02
Fund receivable for research and preclinical activities			$ 60,000,000
Research term under collaboration and license agreement			4 years
Collaboration agreement commencement date	Apr. 2, 2018
Collaboration revenue recognized						1,600,000			$ 3,500,000		7,600,000	$ 6,900,000	17,200,000
Collaboration and license agreement, deferred revenue current						93,600,000					93,600,000		93,600,000	93,600,000
Collaboration and license agreement, accounts receivable						50,000,000					50,000,000		50,000,000	50,000,000
Collaboration and license agreement, accounts receivable current						$ 20,000,000					$ 20,000,000		$ 20,000,000	$ 20,000,000
Collaboration And License Agreement [Member] | Takeda [Member] | Category One Programs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of global costs and potential profits sharing ratio			50.00%
Collaboration And License Agreement [Member] | Takeda [Member] | Category Two Programs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Fund receivable for research and preclinical activities			$ 60,000,000
Research term under collaboration and license agreement			4 years
Maximum targets for preclinical programs | Target			6
Option to reach maximum targets for preclinical programs											any one time
Collaboration And License Agreement [Member] | Takeda [Member] | Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement, committed cash				$ 230,000,000
Collaboration and Share Purchase Agreements [Member] | Takeda [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued under equity agreement | shares			1,096,892
Purchase price per share | $ / shares			$ 54.70
Proceeds from issuance of ordinary shares, net of offering costs			$ 60,000,000
Equity investment agreement official closure month and year			2018-04

Net Loss Per Ordinary Share - A

Net Loss Per Ordinary Share - Anti-Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Ordinary Share (Detail) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Options to Purchase Ordinary Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from calculation of diluted net loss per share	3,902,994	3,912,336
RSUs [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from calculation of diluted net loss per share	1,744,177	408,534
Series A Preferred Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from calculation of diluted net loss per share	3,901,348	3,901,348

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income tax benefit (provision)	$ 0	$ 0	$ 0	$ (172,000)

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($)	9 Months Ended	27 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 26, 2016	Apr. 30, 2015
Operating Leased Assets [Line Items]
Restricted cash	$ 3,643,000	$ 3,625,000
Lexington, Massachusetts [Member]
Operating Leased Assets [Line Items]
Lease agreement term			10 years 9 months
Renewal options	10 year and 9 month lease, which includes two successive five year renewal options
Restricted cash	$ 2,600,000	2,600,000
Lease renewal term			5 years
Tenant improvement allowances received		11,400,000
Cambridge, Massachusetts [Member]
Operating Leased Assets [Line Items]
Lease agreement term				7 years 6 months
Restricted cash	$ 1,000,000	$ 1,000,000
Lease renewal term				5 years
Lease option to extend description	five-year renewal option to extend the lease
Option to extend the lease	true

Leases - Summary of Lease Costs

Leases - Summary of Lease Costs Recognized and Other Inforation Pertaining to the Operating Leases (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2019USD ($)
Lease cost
Operating lease cost	$ 3,354
Total lease cost	3,354
Other information
Operating cash flows used for operating leases	$ 4,233
Weighted average remaining lease term	7 years 6 months
Weighted average discount rate	8.50%

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Lease Payments Under 842 (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019
Operating Lease Liabilities, Payments Due [Abstract]
2019	$ 1,442
2020	5,846
2021	6,021
2022	6,201
2023	5,236
Thereafter	20,927
Total lease payments	45,673
Less: imputed interest	(12,376)
Total operating lease liabilities	$ 33,297	$ 35,400

Related Parties - Additional In

Related Parties - Additional Information (Detail) - Scientific Advisor [Member] - Consulting Agreement [Member] $ in Thousands	9 Months Ended
	Sep. 30, 2019USD ($)
Related Party Transaction [Line Items]
Consulting agreement termination notice period	14 days
Consulting service expenses	$ 13