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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2018	Feb. 22, 2019	Jun. 29, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	NTLA
Entity Registrant Name	INTELLIA THERAPEUTICS, INC.
Entity Central Index Key	0001652130
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		45,225,345
Entity Public Float			$ 1,108,565,339

Consolidated Balance Sheets - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 58,856,000	$ 340,678,000
Marketable securities	255,203,000	0
Accounts receivable	7,547,000	10,471,000
Prepaid expenses and other current assets	3,371,000	3,681,000
Total current assets	324,977,000	354,830,000
Property and equipment, net	17,061,000	15,272,000
Other assets	5,277,000	6,133,000
Total Assets	347,315,000	376,235,000
Current Liabilities:
Accounts payable	2,708,000	2,172,000
Accrued expenses	10,742,000	7,999,000
Current portion of deferred revenue	27,122,000	21,188,000
Total current liabilities	40,572,000	31,359,000
Deferred revenue, net of current portion	28,810,000	44,111,000
Other long-term liabilities	13,000	168,000
Commitments and contingencies (Note 6)
Stockholders’ Equity:
Common stock, $0.0001 par value; 120,000,000 shares authorized; 45,224,480 and 42,384,623 shares issued and outstanding at December 31, 2018 and 2017, respectively	5,000	4,000
Additional paid-in capital	478,968,000	421,706,000
Accumulated other comprehensive loss	(28,000)
Accumulated deficit	(201,025,000)	(121,113,000)
Total stockholders’ equity	277,920,000	300,597,000
Total Liabilities and Stockholders’ Equity	$ 347,315,000	$ 376,235,000

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	45,224,480	42,384,623
Common stock, shares outstanding	45,224,480	42,384,623

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Collaboration revenue	$ 30,434	$ 26,117	$ 16,479
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses:
Research and development	$ 89,115	$ 67,647	$ 31,840
General and administrative	32,189	28,025	16,798
Total operating expenses	121,304	95,672	48,638
Operating loss	(90,870)	(69,555)	(32,159)
Interest income	5,527	2,012	525
Net loss	$ (85,343)	$ (67,543)	$ (31,634)
Net loss per share, basic and diluted	$ (1.98)	$ (1.88)	$ (1.42)
Weighted average shares outstanding, basic and diluted	43,069	36,006	22,222
Other comprehensive loss:
Unrealized loss on marketable securities	$ (28)
Comprehensive loss	$ (85,371)	$ (67,543)	$ (31,634)

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Accumulated Other Comprehensive Income [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2015	$ (21,201)			$ 735	$ (21,936)
Beginning balance, shares at Dec. 31, 2015		2,558,755
Conversion of convertible preferred stock	88,557	$ 3		88,554
Conversion of convertible preferred stock, shares		23,481,956
Issuance of units/stock	167,139	$ 1		167,138
Issuance of units/stock, shares		9,955,554
Exercise of stock options	2			2
Exercise of stock options, shares		257
Issuance of shares under employee stock purchase plan	259			259
Issuance of shares under employee stock purchase plan, shares		23,209
Equity-based compensation	6,715			6,715
Equity-based compensation, shares		(1,191)
Net loss	(31,634)				(31,634)
Ending balance at Dec. 31, 2016	209,837	$ 4		263,403	(53,570)
Ending balance, shares at Dec. 31, 2016		36,018,540
Issuance of units/stock	141,000			141,000
Issuance of units/stock, shares		6,250,000
Exercise of stock options	1,156			1,156
Exercise of stock options, shares		141,759
Issuance of shares under employee stock purchase plan	825			825
Issuance of shares under employee stock purchase plan, shares		64,786
Equity-based compensation	15,322			15,322
Equity-based compensation, shares		(90,462)
Net loss	(67,543)				(67,543)
Ending balance at Dec. 31, 2017	$ 300,597	$ 4		421,706	(121,113)
Ending balance, shares at Dec. 31, 2017	42,384,623	42,384,623
Retroactive adjustment to beginning accumulated deficit for adoption of ASU 2014-09 at Dec. 31, 2018	$ 5,431				5,431
Issuance of units/stock	28,548	$ 1		28,547
Issuance of units/stock, shares		1,659,300
Exercise of stock options	$ 10,651			10,651
Exercise of stock options, shares	1,142,944	1,142,944
Issuance of shares under employee stock purchase plan	$ 1,018			1,018
Issuance of shares under employee stock purchase plan, shares		68,865
Equity-based compensation	17,046			17,046
Equity-based compensation, shares		(31,252)
Other comprehensive loss	(28)		$ (28)
Net loss	(85,343)				(85,343)
Ending balance at Dec. 31, 2018	$ 277,920	$ 5	$ (28)	$ 478,968	$ (201,025)
Ending balance, shares at Dec. 31, 2018	45,224,480	45,224,480

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
Common Stock [Member]
Units/stock issuance cost	$ 424	$ 3,367

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (85,343)	$ (67,543)	$ (31,634)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	4,464	2,994	1,104
Loss on disposal of property and equipment	75	166	13
Equity-based compensation	17,046	15,322	6,715
Accretion of investment discounts	(676)
Changes in operating assets and liabilities:
Accounts receivable	2,924	(4,017)	(5,454)
Prepaid expenses and other current assets	310	(1,893)	(979)
Accounts payable	232	(488)	1,784
Accrued expenses	2,780	2,394	3,050
Deferred revenue	(3,936)	(12,988)	67,975
Other assets	1,022	902	(6,435)
Other long-term liabilities	(155)	(125)	(30)
Net cash (used in) provided by operating activities	(61,257)	(65,276)	36,109
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(6,358)	(10,091)	(6,165)
Proceeds from sale of property and equipment	131
Purchases of marketable securities	(254,555)
Net cash used in investing activities	(260,782)	(10,091)	(6,165)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments to acquire in-process research and development			(600)
Payment of preferred unit and preferred stock issuance costs			(100)
Proceeds from common stock offering	28,971	141,000	170,507
Proceeds from options exercised	10,652	1,156	2
Issuance of shares through employee stock purchase plan	1,018	825	259
Payment of common stock offering costs	(424)		(2,764)
Net cash provided by financing activities	40,217	142,981	167,304
Net (decrease) increase in cash and cash equivalents	(281,822)	67,614	197,248
Cash and cash equivalents, beginning of period	340,678	273,064	75,816
Cash and cash equivalents, end of period	58,856	340,678	273,064
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Purchases of property and equipment unpaid at period end	$ 1,071	$ 805	3,090
Conversion of convertible preferred stock to common stock			$ 88,557

The Company

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

The Company

1. The Company

Intellia Therapeutics, Inc. (“Intellia” or the “Company”) is a genome editing company focused on developing curative therapeutics utilizing CRISPR/Cas9 technology both in vivo and ex vivo.

The Company was founded and commenced active operations in mid-2014. The Company will require substantial additional capital to fund its research and development. The Company is subject to risks and uncertainties common to early stage companies in the biotechnology industry, including, but not limited to, development by competitors of more advanced or effective therapies, dependence on key executives, protection of and dependence on proprietary technology, compliance with government regulations and ability to secure additional capital to fund operations. Programs currently moving into development will require significant additional research and development efforts, including preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The consolidated financial statements include the accounts of Intellia Therapeutics, Inc. and its wholly owned, controlled subsidiary, Intellia Securities Corp. All intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of the Company’s consolidated financial statements in accordance with accounting principles generally accepted in the United States of America (“U.S.”) requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition and the valuation of common and incentive units for the periods prior to the Company’s stock becoming publicly traded. Estimates are periodically reviewed in light of changes in circumstances, facts and experiences. Actual results may differ materially from management’s estimates, judgments and assumptions.

Fair Value Measurements

The Company classifies fair value-based measurements using a three-level hierarchy that prioritizes the inputs used to measure fair value. This hierarchy requires entities to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of inputs used to measure fair value are as follows: Level 1, quoted market prices in active markets for identical assets or liabilities; Level 2, observable inputs other than quoted market prices included in Level 1, such as quoted market prices for markets that are not active or other inputs that are observable or can be corroborated by observable market data; and Level 3, unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities, including certain pricing models, discounted cash flow methodologies and similar techniques that use significant unobservable inputs.

As of December 31, 2018 and 2017, the Company’s financial instruments included cash and cash equivalents, marketable securities, accounts receivable and accounts payable. As of December 31, 2018 and 2017, the Company’s financial assets recognized at fair value on a recurring basis consisted of the following:

	Fair Value as of December 31, 2018
	Total		Level 1		Level 2		Level 3
	(In thousands)
Cash equivalents	$	45,986	$	45,986	$	-	$	-
Marketable securities		255,203		165,948		89,255		-
Total	$	301,189	$	211,934	$	89,255	$	-

	Fair Value as of December 31, 2017
	Total		Level 1		Level 2		Level 3
	(In thousands)
Cash equivalents	$	330,896	$	330,896	$	-	$	-
Total	$	330,896	$	330,896	$	-	$	-

The Company’s financial assets, which include cash equivalents and marketable securities, have been initially valued at the transaction price, and subsequently revalued at the end of each reporting period, utilizing third-party pricing services or other observable market data. The pricing services utilize industry standard valuation models and observable market inputs to determine value. After completing our validation procedures, we did not adjust or override any fair value measurements provided by the pricing services as of December 31, 2018.

Other financial instruments, including accounts receivable and accounts payable, are carried at cost, which approximate fair value due to the short duration and term to maturity.

Cash Equivalents

The Company considers all highly liquid investments with maturities of three months or less when purchased to be cash equivalents. As of December 31, 2018 and 2017, cash equivalents consisted of interest-bearing money market accounts, commercial paper and U.S. treasury securities.

Marketable Securities

The following table summarizes the Company’s available-for-sale marketable securities as of December 31, 2018 at net book value:

	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(In thousands)
Short-term marketable securities:
U.S. Treasury securities	$	165,959	$	2	$	(13	)	$	165,948
Financial institution debt securities		65,436		1		(17	)		65,420
Corporate debt securities		23,836		-		(1	)		23,835
Total	$	255,231	$	3	$	(31	)	$	255,203

The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. At December 31, 2018, the balance in the Company’s accumulated other comprehensive loss was composed of activity related to the Company’s available-for-sale marketable securities. There were no realized gains or losses in the period ended December 31, 2018, and as a result, the Company did not reclassify any amounts out of accumulated other comprehensive loss during the period. The Company did not have any securities in a material unrealized loss position at December 31, 2018. The Company held no marketable securities at December 31, 2017.

Concentrations of Credit Risk

The Company’s cash, cash equivalents and marketable securities may potentially be subject to concentrations of credit risk. The Company generally maintains balances in various accounts in excess of federally insured limits with financial institutions that management believes to be of high credit quality.

Accounts receivable represent amounts due from collaboration partners. The Company monitors economic conditions to identify facts or circumstances that may indicate that any of its accounts receivable are at risk of collection. As of December 31, 2018 and 2017, the Company’s two collaboration partners, Regeneron Pharmaceuticals, Inc. (“Regeneron”) and Novartis Institutes for BioMedical Research, Inc. (“Novartis”), accounted for all of the Company’s accounts receivable.

Property and Equipment

The Company records property and equipment at cost and recognizes depreciation and amortization using the straight-line method over the following estimated useful lives of the respective assets:

Asset Category		Useful Life
Laboratory equipment		5 years
Office furniture and equipment		5 years
Computer software		3 years
Computer equipment		3 years
Leasehold improvements		5 years or term of respective lease, if shorter

Expenditures for repairs and maintenance of assets are expensed as incurred. Upon retirement or sale, the cost of assets disposed and the corresponding accumulated depreciation are removed from the related accounts and any resulting gain or loss is reflected in the results of operations.

Impairment of Long-Lived Assets

The Company tests long-lived assets to be held and used, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of assets or asset groups may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets.

Evaluation of recoverability of the asset or asset group is based on an estimate of undiscounted future cash flows resulting from the use of the asset or asset group and its eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the asset or asset group, the assets are written down to their estimated fair values. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any material impairment losses on long-lived assets.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences attributable to differences between carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax reporting purposes and for operating loss and tax credit carryforwards. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes.

The Company’s deferred tax assets and liabilities are measured using enacted tax rates expected to apply in the years in which these temporary differences are expected to be recovered or settled. A valuation allowance is recorded to reduce deferred tax assets if it is determined that it is more likely than not that all or a portion of the deferred tax asset will not be realized. The Company considers many factors when assessing the likelihood of future realization of deferred tax assets, including recent earnings results, expectations of future taxable income, carryforward periods available and other relevant factors. The Company records changes in the required valuation allowance in the period that the determination is made.

The Company assesses its income tax positions and records tax benefits for all years subject to examination based upon management’s evaluation of the facts, circumstances and information available as of the reporting date. For those tax positions where it is more likely than not that a tax benefit will be sustained, the Company records the largest amount of tax benefit with a greater than 50 percent likelihood of being realized upon ultimate settlement with a taxing authority having full knowledge of all relevant information. For those income tax positions where it is not more likely than not that a tax benefit will be sustained, the Company does not recognize a tax benefit in the financial statements. The Company records interest and penalties related to uncertain tax positions, if applicable, as a component of income tax expense.

Revenue Recognition

The Company adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606) and its related amendments (collectively known as “ASC 606”) on January 1, 2018 using the modified retrospective method. The reported results for 2018 reflect the application of ASC 606 guidance while the reported results for 2017 and 2016 were prepared under the guidance of ASC 605, Revenue Recognition (“ASC 605” or “legacy GAAP”). The adoption of ASC 606 represents a change in accounting principle that will more closely align revenue recognition with the delivery of the Company’s goods and services and will provide financial statement readers with enhanced disclosures.

At inception, the Company determines whether contracts are within the scope of ASC 606 or other topics. For contracts that are determined to be within the scope of ASC 606, revenue is recognized when a customer obtains control of promised goods or services. The amount of revenue recognized reflects the consideration to which the Company expects to be entitled to receive in exchange for these goods and services. To achieve this core principle, the Company applies the following five steps (i) identify the contract with the customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when or as the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when the Company determines that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration.

Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct and are distinct in the context of the contract. To the extent a contract includes multiple promised goods and services, the Company applies judgment to determine whether promised goods and services are both capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation.

The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing either the expected value method or the most likely amount method, depending on the nature of the variable consideration. Variable consideration is included in the transaction price if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Any estimates, including the effect of the constraint on variable consideration, are evaluated at each reporting period for any changes. Determining the transaction price requires significant judgment, which is discussed in further detail for each of the Company’s collaboration agreements in Note 7. In addition, neither of the Company’s contracts as of December 31, 2018 contained a significant financing component.

If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices. The Company typically determines standalone selling prices using an adjusted market assessment approach model.

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

As of December 31, 2018, the Company’s only revenue recognized is related to collaboration agreements with third parties which are either within the scope of ASC 606, under which the Company licenses certain rights to its product candidates to third parties, or within the scope of ASC 808, if it involves a joint operating activity pursuant to which the Company is an active participant and is exposed to significant risks and rewards with respect to the arrangement. For the collaboration arrangements under the scope of ASC 606, as discussed in further detail in Note 7, the terms of these arrangements typically include payment to the Company of one or more of the following: nonrefundable, upfront fees; development, regulatory, and commercial milestone payments; research and development funding payments; and royalties on the net sales of licensed products. Each of these payments results in collaboration revenues, except for revenues from royalties on the net sales of licensed products, which are classified as royalty revenues. For arrangements within the scope of ASC 808, the terms of these arrangements typically include payments received or made under the cost sharing provisions which are recognized as a component of revenues in the consolidated statements of operations.

Licenses of intellectual property (“IP”): If the license to the Company’s IP is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from consideration allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the licenses. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

Milestone payments: At the inception of each arrangement that includes development milestone payments, the Company evaluates the probability of reaching the milestones and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur in the future, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received and therefore revenue recognized is constrained as management is unable to assert that a reversal of revenue would not be possible. The transaction price is then allocated to each performance obligation on a relative standalone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenues and earnings in the period of adjustment.

Royalties: For arrangements that include sales-based royalties, including milestone payments based on levels of sales, if the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its collaboration agreements.

The Company receives payments from its customers based on billing schedules established in each contract. The Company’s contract liabilities consist of deferred revenue. Upfront payments and fees are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company satisfies its obligations under these arrangements.

The Company also considers the nature and contractual terms of an arrangement and assesses whether the arrangement involves a joint operating activity pursuant to which the Company is an active participant and is exposed to significant risks and rewards with respect to the arrangement. If the Company is an active participant and is exposed to the significant risks and rewards with respect to the arrangement, the Company accounts for the arrangement under ASC 808, Collaborative Arrangements. Based on this consideration, the Company accounts for its Co-Development and Co-Promotion Agreement with Regeneron under ASC 808. Because ASC 808 does not provide recognition and measurement guidance for collaborative arrangements, the Company has analogized to ASC 606. Refer to Note 7 for additional information regarding the Company’s collaboration agreements.

The following table presents changes in the Company’s contract liabilities during the year ended December 31, 2018 (in thousands):

	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
Year Ended December 31, 2018
Contract liabilities:
Deferred revenue	$	59,868	$	19,000	$	(22,936	)	$	55,932

During the year ended December 31, 2018, the Company recognized the following revenues as a result of changes in the contract liability balance (in thousands):

Revenue recognized in the period from:

Year Ended

December 31, 2018

Amounts included in the contract liability at the beginning of the period

22,936

Costs to obtain and fulfill a contract

The Company did not incur any expenses to obtain collaboration agreements and costs to fulfill those contracts do not generate or enhance resources of the Company. As such, no costs to obtain or fulfill a contract have been capitalized in any period.

Research and Development Expenses

Research and development costs are expensed as incurred. Research and development expenses consist of salaries, equity-based compensation and benefits of employees, lab supplies and materials, facilities expenses, overhead expenses, fees paid to subcontractors and contract research organizations and other external expenses.

The Company records payments made for research and development services prior to the services being rendered as prepaid expense on the consolidated balance sheet and expenses them as the services are provided. Contracts for multi-year research and development services are recorded on a straight-line basis over each annual contractual period based on the total contractual fee when the services rendered are expected to be substantially equivalent over the term of the arrangement. The cost of obtaining licenses for certain technology or IP is recorded to research and development expense when incurred if the licensed technology or IP has not yet reached technological feasibility and has no alternative future use.

Equity-Based Compensation

The Company measures employee equity-based compensation based on the grant date fair value of the equity awards using the Black-Scholes option pricing model. Equity-based compensation expense is recognized on a straight-line basis over the requisite service period of the awards and is adjusted for pre-vesting forfeitures in the period in which the forfeitures occur. For equity awards that have a performance condition, the Company recognizes compensation expense based on its assessment of the probability that the performance condition will be achieved.

The Company measures equity awards granted to consultants and non-employees based on the fair value of the award on the date each portion of the award vests, which represents when the Company receives the related goods or services. Compensation expense is recognized over the period during which services are rendered by such consultants and non-employees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of these awards is remeasured using the then-current fair value of that equity award.

The Company classifies equity-based compensation expense in its consolidated statement of operations in the same manner in which the award recipient’s salary and related costs are classified or in which the award recipient’s service payments are classified.

(Loss) Earnings per Share

The Company calculates basic (loss) earnings per share by dividing (loss) income by the weighted average number of common shares outstanding. The Company computes diluted (loss) earnings per share after giving consideration to the dilutive effect of stock options and unvested restricted stock awards that are outstanding during the period, except where such non-participating securities would be anti-dilutive.

Segment Information

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s one business segment is the development of genome editing-based therapies. All of the Company’s assets are held in the U.S. and all of the Company’s revenue has been generated in the U.S.

Recent Accounting Pronouncements

In May 2014, the FASB issued ASC 606, which superseded existing revenue recognition guidance. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The Company adopted ASC 606 effective on January 1, 2018 using the modified retrospective method. Please see the above “Revenue Recognition” section for a discussion of the Company’s updated policies related to revenue recognition and accounting for costs to obtain and fulfill a customer contract.

Impact of Adoption

The Company adopted ASC 606 using the modified retrospective method. The cumulative effect of applying the new guidance to all contracts with customers that were not completed as of January 1, 2018 was recorded as an adjustment to accumulated deficit as of the adoption date. As a result of applying the modified retrospective method to adopt the new guidance, the following adjustments were made to accounts on the consolidated balance sheet as of January 1, 2018:


Consolidated Balance Sheet	January 1, 2018 (in thousands)
	Pre-Adoption			ASC 606 Adjustment			Post-Adoption
Current portion of deferred revenue	$	21,188		$	(2,769	)	$	18,419
Deferred revenue, net of current portion		44,111			(2,662	)		41,449
Accumulated deficit		(121,113	)		5,431			(115,682	)


	Year Ended December 31, 2018
	Impact of changes in accounting policies
	As Reported			Balances without adoption of ASC 606			Effect of Change Higher/(Lower)
Collaboration revenue	$	30,434		$	31,838		$	(1,404	)
Operating loss		(90,870	)		(89,466	)		(1,404	)
Net loss	$	(85,343	)	$	(83,939	)	$	(1,404	)
Net loss per share, basic and diluted	$	(1.98	)	$	(1.95	)	$	(0.03	)

	December 31, 2018
	Impact of changes in accounting policies
	As Reported			Balances without adoption of ASC 606			Effect of Change Higher/(Lower)
Liabilities:
Deferred revenue – current	$	27,122		$	31,149		$	(4,027	)
Deferred revenue – noncurrent		28,810			28,810			-
Stockholders' equity:
Accumulated deficit	$	(201,025	)	$	(205,052	)	$	4,027

In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (“ASC 808”). This update provides clarification on the interaction between Revenue Recognition (“ASC 606”) and Collaborative Arrangements including the alignment of unit of account guidance between the two topics. ASC 808 becomes effective for the Company in the first quarter of fiscal 2021 with early adoption permitted. The Company early adopted this ASU and it did not have a material effect on its consolidated financial statements.

In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”). ASU 2016-02 establishes ASC Topic 842 which amends ASC 840, Leases, by introducing a lessee model that requires balance sheet recognition for most leases and the disclosure of key information about leasing arrangements. Leases will be classified as finance or operating, with classification affecting the pattern and classification of expense recognition in the income statement. Topic 842 was subsequently amended during 2018. The Company will adopt the new standard on January 1, 2019 and use the effective date as its date of initial application. Consequently, financial information will not be updated and the disclosures required under the new standard will not be provided for dates and periods prior to January 1, 2019.

Topic 842 provides several optional practical expedients in transition. The Company expects to elect the package of practical expedients which would allow the Company to not reassess its existing conclusions on lease identification, classification, and initial direct costs. Further, the Company expects to elect the hindsight practical expedient and to utilize the short-term lease exemption for all leases with an original term of 12 months or less, for purposes of applying the recognition and measurement requirements of the new standard. The Company also expects to elect the practical expedient which will allow it to not separate lease and non-lease components for all its leases.

The adoption of the new standard is expected to result in the recognition of additional lease liabilities ranging from $19.0 million to $21.0 million, and right-of-use assets ranging from $21.0 million to $23.0 million as of January 1, 2019. The Company does not expect that the new standard will have a material impact to the Company’s consolidated statement of operations or cash flows. See Note 6 for additional information related to the Company’s lease obligations.

In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, (“ASU 2018-13”). The new standard removes certain disclosures, modifies certain disclosures and adds additional disclosures related to fair value measurement. The new standard will be effective beginning January 1, 2020 and early adoption is permitted. The Company is currently evaluating the potential impact ASU 2018-13 may have on its disclosures upon adoption.

In June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”), which simplifies the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees, with certain exceptions. The new standard will be effective beginning January 1, 2019; the Company does not expect that the new standard will have a material impact to the Company’s consolidated financial statements.

Property and Equipment, Net

12 Months Ended

Dec. 31, 2018

Property Plant And Equipment [Abstract]

Property and Equipment, Net

3. Property and Equipment, Net

Property and equipment, net consisted of the following:

	December 31,
	2018			2017
	(in thousands)
Laboratory equipment	$	22,453		$	16,704
Office furniture and equipment	960			960
Computer equipment	929			845
Leasehold improvements	898			656
Computer software	433			436
Total property and equipment		25,673			19,601
Less: accumulated depreciation and amortization		(8,612	)		(4,329	)
Property and equipment, net	$	17,061		$	15,272

Depreciation and amortization expense was $4.5 million, $3.0 million and $1.1 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Accrued Expenses

12 Months Ended

Dec. 31, 2018

Payables And Accruals [Abstract]

Accrued Expenses

4. Accrued Expenses

Accrued expenses consisted of the following:

	December 31, 2018		December 31, 2017
	(In thousands)
Employee compensation and benefits	$	6,175	$	4,773
Accrued research and development		2,328		1,960
Accrued legal and professional expenses		1,633		587
Accrued other		606		679
Total accrued expenses	$	10,742	$	7,999

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

5. Income Taxes

The Company did not record net income tax benefits for the operating losses incurred during the periods presented due to the uncertainty of realizing a tax benefit from those losses. Accordingly, any benefit recorded related to these deferred tax assets was offset by a valuation allowance reflecting management’s conclusion that realization of those assets was not more likely than not.

A reconciliation of the federal statutory income tax rate and the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2018			2017			2016
Federal statutory income tax rate		(21.0	)%		(34.0	)%		(34.0	)%
State income taxes		(8.6	)		(6.9	)		(6.7	)
Research and development tax credits		(4.7	)		(3.4	)		(2.8	)
Stock-based compensation		(0.6	)		3.6			1.9
Change in U.S. tax rate		-			18.7			-
Change in valuation allowance		34.9			22.0			41.6
Effective income tax rate		-	%		-	%		-	%

The Company’s net deferred tax assets (liabilities) consisted of the following:

	December 31,
	2018			2017
	(in thousands)
Deferred tax assets:
Intangibles, including acquired in-process research and development	$	1,201		$	1,303
Capitalized start-up costs		463			502
Net operating loss carryforwards		34,234			9,406
Research and development credit carryforwards		11,766			5,817
Deferred revenue		12,199			15,913
Equity-based compensation		4,064			3,248
Accruals and allowances		1,359			1,112
Gross deferred tax assets		65,286			37,301
Deferred tax asset valuation allowance		(64,046	)		(35,372	)
Total deferred tax assets		1,240			1,929
Deferred tax liabilities:
Fixed assets		(1,240	)		(1,929	)
Total deferred tax liabilities		(1,240	)		(1,929	)
Net deferred tax asset (liability)	$	-		$	-

As of December 31, 2018, the Company had federal and state net operating loss carryforwards of $128.2 million and $117.0 million, respectively, which begin to expire in 2034. As of December 31, 2018, the Company had federal and state research and development tax credit carryforwards of approximately $7.5 million and $4.8 million, which begin to expire in 2034 and 2030, respectively.

The Company evaluated the expected realizability of its net deferred tax assets and determined that there was significant negative evidence due to its net operating loss position and insufficient positive evidence to support the realizability of these net deferred tax assets. The Company concluded it is more likely than not that its net deferred tax assets would not be realized in the future; therefore, the Company has provided a full valuation allowance against its net deferred tax asset balance as of December 31, 2018 and 2017. The valuation allowance increased by $28.7 million in 2018, $14.8 million in 2017 and $13.1 million in 2016.

Utilization of the net operating loss and research and development credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of net operating loss and research and development credit carryforwards that can be utilized annually to offset future taxable income and tax expense, respectively. The Company has not yet conducted a study to assess whether a change of control, as defined in Section 382, has occurred or whether there have been multiple changes in control since inception.

As of December 31, 2018, the Company had not identified any unrecognized tax benefits. The Company files income tax returns in the U.S. federal tax jurisdiction and Massachusetts and various other state tax jurisdictions. The Company is subject to examination by the Internal Revenue Service and Massachusetts taxing authorities. The returns in these jurisdictions since inception remain open for examination; however, there are currently no pending tax examinations.

On December 22, 2017, the Tax Cuts and Jobs Act (“TCJA”) was enacted. This law substantially amended the Internal Revenue Code and among other things, permanently reduced the U.S. corporate income tax rate from 35 percent to 21 percent. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (“SAB 118”), which allows the recording of provisional amounts during a measurement period not to extend beyond one year of the enactment date. As a result of remeasuring the deferred tax assets and liabilities to the lower tax rate, the net deferred tax assets decreased by $12.6 million, which was offset by a decrease in the valuation allowance.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

6. Commitments and Contingencies

Commitments

Property Leases

In October 2014, the Company entered into an agreement to lease office and laboratory space in Cambridge, Massachusetts under an operating lease agreement with a term through January 2020, with an option to extend the term of the lease for an additional five-year period which the Company plans to execute. Upon the execution of the original lease, the Company provided a $0.3 million security deposit. The Company has recorded this security deposit in other assets on the consolidated balance sheets. In January 2016, the Company entered into a ten-year agreement to lease office and laboratory space in Cambridge, Massachusetts under an operating lease agreement, with an option to terminate the lease at the end of the sixth year and an option to extend the term of the lease for an additional three years. Upon the execution of this lease, the Company provided a $2.2 million security deposit, which has been recorded in other assets on the consolidated balance sheets. In addition, the Company had prepaid $2.2 million in lease payments as of December 31, 2018 under the terms of this lease.

The Company recognizes rent expense, inclusive of escalation charges, on a straight-line basis over the initial term of the lease agreements. The Company recorded rent expense of $6.2 million, $6.0 million and $2.7 million during the years ended December 31, 2018, 2017 and 2016, respectively.

Future minimum lease payments under the Company’s property leases as of December 31, 2018 are as follows:

Year Ending December 31,	(In thousands)
2019	$	5,616
2020		4,963
2021		5,507
2022		3,861
Thereafter		-
	$	19,947

Contingencies

In connection with a July 2014 IP license with Caribou Biosciences, Inc. (“Caribou”), a stockholder who held 5.5 percent of the Company’s common stock at December 31, 2018, the Company gained access to sublicensed IP from various academic and professional institutions. Under these sublicenses, the Company may be obligated to pay development and regulatory milestones of up to $6.4 million, sales-based milestones of up to $20.0 million and up to mid-single-digit royalties on net sales of any products covered by issued patents to these entities in certain circumstances.

Collaborations

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Collaborations

7. Collaborations

To accelerate the development and commercialization of CRISPR/Cas9-based products in multiple therapeutic areas, the Company has formed, and intends to seek other opportunities to form, strategic alliances with collaborators who can augment its leadership in CRISPR/Cas9 therapeutic development.

Novartis Institutes for BioMedical Research, Inc. (“Novartis”)

In December 2014, the Company entered into a strategic collaboration agreement with Novartis (the “Novartis Agreement”) with Novartis primarily focused on the development of new ex vivo CRISPR/Cas9-edited therapies using chimeric antigen receptor T cells (“CAR-T cell”s) and hematopoietic stem cells (“HSC”s).

Agreement Structure. The parties agreed to engage in collaborative research activities using its CRISPR/CAS9 platform to identify and research therapeutic, prophylactic and palliative products and services relating to the following applications: a) ex vivo HSCs and, b) ex vivo CAR-Ts. In addition, in the last two years of the collaboration term, Novartis may engage in research and development of a limited number of in vivo targets using the Company’s platform.

Scope of Collaboration. During the five-year collaboration term parties may research potential therapeutic, prophylactic and palliative ex vivo applications of the CRISPR/Cas9 technology in HSCs and CAR-T cells. Research expenses incurred by the Company in support of the collaboration are reimbursed by Novartis.

HSC Program. The Company and Novartis agreed to conduct research of HSC targets under a research plan agreed upon by both parties. Within the HSC therapeutic space, Novartis may obtain exclusive rights to a limited number of these HSC targets, to be selected by Novartis in a series of selection windows. The Company has the right to choose a limited number of HSC targets for its exclusive development and commercialization per the specified selection schedule. Following these selections by Novartis and the Company, Novartis may obtain rights to research an additional limited number of HSC targets on a non-exclusive basis. Novartis is required to use commercially reasonable efforts to research, develop and commercialize at least one HSC product directed to each of their selected HSC targets.

CAR-T Program. The Company has also agreed to collaborate with Novartis on research activities for CAR-T cell targets. After completion of the activities contemplated by the parties’ CAR-T cell program research plan, Novartis will assume sole responsibility for developing any products that it selects, arising from that research plan and the costs and expenses of developing, manufacturing and commercializing its selected research targets. Novartis is required to use commercially reasonable efforts to research, develop or commercialize at least one CAR-T cell product directed to each of its selected CAR-T cell targets.

In Vivo Program. During the last two years of the five-year collaboration term, Novartis has the option to select a limited number of targets for research, development and commercialization of in vivo therapies using the Company’s CRISPR/Cas9 platform, on a non-exclusive basis. Following Novartis’ selection of each in vivo target, Novartis may offer the Company the right to participate in the research and development of such targets, in which case an in vivo program research plan for such target will be entered into between the Company and Novartis. Novartis is required to use commercially reasonable efforts to research, develop or commercialize at least one in vivo product directed to each of its selected targets. Novartis’ in vivo target selections are subject to certain restrictions, including that the targets, or all targets within a limited number of organs: (i) have not already been reserved by the Company pursuant to its limited right to do so under the agreement; (ii) are not the subject of a collaboration or pending collaboration with a third party; and (iii) are not the subject of ongoing or planned research and development by the Company.

Governance. The parties formed HSC and CAR-T steering committees with responsibility for oversight of these respective research programs and approval of the associated research plans. The HSC steering committee is also responsible for the OSC program. These steering committees in turn are overseen by a joint steering committee. The above steering committees are comprised by an equal number of representatives from each party.

Financial Terms. The Company received an upfront technology access payment from Novartis of $10.0 million in January 2015 and is entitled to additional technology access fees of $20.0 million and quarterly research payments of $1.0 million, or up to $20.0 million in the aggregate, during the five-year research term. To date, the Company has received $15.0 million in technology access fees and $15.0 million in research payments related to these programs. In addition, for each Novartis product under the collaboration (whether HSC or CAR-T, and as of December 2018, OSC), subject to certain conditions, the Company may be eligible to receive (i) up to $30.3 million in development milestones, including for the filing of an investigational new drug (“IND”) application and for the dosing of the first patient in each of Phase IIa, Phase IIb and Phase III clinical trials, (ii) up to $50.0 million in regulatory milestones for the product’s first indication, including regulatory approvals in the U.S. and European Union (“EU”), (iii) up to $50.0 million in regulatory milestones for the product’s second indication, if any, including U.S. and EU regulatory approvals, (iv) royalties on net sales in the mid-single digits, and (v) net sales milestone payments of up to $100.0 million. The Company is also eligible to receive payments for: (i) each additional HSC target selected by Novartis beyond its initial defined allocation, for which it will receive $1.0 million for each target (ii) each in vivo target that Novartis selects as described above, and (iii) any exercise by Novartis of certain license options under the agreement.

Upon completion of the research collaboration term in December 2019, Novartis has the option to internalize the Intellia platform for a $50.0 million fee, which will allow them to select a limited number of additional CRISPR/Cas9 genome editing targets over 5 years. Up to $20.0 million of the internalization fee will be credited towards any milestone payments for any additional post-internalization targets (up to $4.0 million per target).

Equity Investments. Additionally, at the inception of the arrangement at which time the Company was a privately held company, Novartis invested $9.0 million to purchase the Company’s Class A-1 and Class A-2 Preferred Units. The difference between the cash proceeds received from Novartis for the units and the $11.6 million estimated fair value of those units at the date of issuance was determined to be $2.6 million. Accordingly, $2.6 million of the upfront technology access payment was allocated to record the preferred units purchased by Novartis at fair value.

License Grant to Novartis. In the 2014 Novartis Agreement, the Company granted to Novartis a license to its CRISPR/Cas9 platform technology, including a sublicense to certain platform rights licensed from Caribou, that is exclusive in the HSC, CAR-T cell and in vivo fields with respect to each target selected by Novartis pursuant to the agreement and the research plan as long as Novartis continues to use commercially reasonable efforts to research, develop, and commercialize CRISPR-edited products directed to such targets. Upon the expiration of the collaboration term, Novartis shall have the option to access and obtain a non-exclusive license to the Company’s CRISPR/Cas9 platform technology to research, develop and commercialize potential therapeutic, prophylactic and palliative products and services for a limited number of certain approved targets selected by Novartis, exercisable upon written notice to the Company within 30 days after the expiration of the collaboration term. Such approved targets are subject to certain restrictions, including that the targets may not have been already reserved by the Company pursuant to its limited right to do so under the agreement, may not be the subject of an existing out license of the Company’s CRISPR/Cas9 platform to a third party and may not be the subject of ongoing or planned research and development by the Company. This non-exclusive license will have a term of five years commencing upon the completion of the technology transfer by the Company enabling Novartis to practice such licensed rights, and Novartis may not select more than a specified number of approved targets in each year of this license term.

License Grant to Intellia. Novartis granted the Company a non-exclusive license to its intellectual property covering small molecule for HSC expansion and to its LNP platform technology to research, develop and commercialize HSC and in vivo genome editing products, respectively, in the 2014 Novartis Agreement.

Intellectual Property. IP that the Company develops within the collaboration related to the Company’s CRISPR/Cas9 platform will be owned solely by the Company, while all other IP developed within the collaboration, including IP covering products arising from the collaboration, will be jointly owned by the Company and Novartis.

2018 Amendment to the Agreement

In December 2018, the Company entered into an amendment to this agreement with Novartis (the “Amendment”) which expands the scope of the Novartis Agreement to include the ex vivo development of CRISPR/Cas9-based cell therapies using limbal stem cells, a type of ocular stem cell, primarily against gene targets selected by Novartis in exchange for a one-time payment of $10.0 million which the Company received in December 2018. The governance, milestones and royalties associated with any limbal stem cell program will follow those for the HSC programs. As part of the amendment, Intellia rights to Novartis’ lipid nanoparticle (“LNP”) technology were expanded to include use on all genome editing applications in both in vivo and ex vivo settings.

Term and Termination. The collaboration term ends in December 2019. The term of the agreement expires on the later of (i) the expiration of Novartis’ payment obligations under the agreement and (ii) the date of expiration of the last-to-expire of the patent rights licensed to the Company or Novartis under the agreement. Novartis’ royalty payment obligations expire on a country-by-country and product-by-product basis upon the later of (i) the expiration of the last valid claim of the royalty-bearing patents covering such product in such country or (ii) 10 years after the first commercial sale of such product in such country. The Company may terminate the agreement if Novartis or its affiliates institute a patent challenge against its IP rights, and all improvements thereto, licensed to Novartis under the agreement. Novartis may terminate the agreement, without cause, upon 90 days’ written notice to the Company subject to certain conditions, including its payment of any accrued and future obligations as if the collaboration had continued through December 2019. Either party may terminate the agreement in the event of the other party’s uncured material breach or bankruptcy—or insolvency-related events.

Accounting Analysis. The Company has concluded that the Novartis Agreement is subject to ASC 606 and has assessed the Novartis Agreement accordingly. The Company evaluated the promised goods and services under the Novartis Arrangement and determined that the Novartis Arrangement included two performance obligations: (1) a combined performance obligation representing a series of distinct goods and services including the licenses to research, develop and commercialize HSC products and their associated research activities and the licenses to research, develop and commercialize CAR-T cell products and their associated research activities; and (2) the preferred units.

The Company determined that the transaction price was $59.0 million consisting of the following consideration: (1) the upfront technology access payment of $10.0 million; (2) the additional technology access fees of $20.0 million; (3) the Company’s estimate of variable consideration of $20.0 million related to the quarterly research payments; and (4) the payment for the preferred units of $9.0 million. None of the clinical or regulatory milestones were included in the transaction price, as all milestone amounts were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon future regulatory progress and the licensee’s efforts. Any consideration related to sales-based milestones and royalties will be recognized when the related sales occur as they were determined to relate predominantly to the licenses granted to Novartis and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and when events whose outcomes are resolved or other changes in circumstances occur.

The Company first allocated $11.6 million of the transaction price to the preferred units to record the preferred units purchased by Novartis at fair value. The Company then allocated the remaining $47.4 million of the transaction price to the remaining combined performance obligation of the licenses and associated research activities for HSC and CAR-T cell products. Revenue allocated to the combined performance obligation of the licenses and associated research activities for HSC and CAR-T cell products is being recognized on a straight-line basis over a period of five years, which, in management’s judgment, is the best measure of progress towards satisfying the performance obligation and represents the Company’s best estimate of the period of the obligation.

Revenue Recognition - Collaboration Revenue. Through December 31, 2018, excluding amounts allocated to Novartis’ purchase of the Company’s Class A-1 and Class A-2 Preferred Units, the Company had recorded a total of $53.4 million in cash and accounts receivable under the Novartis Arrangement. Through December 31, 2018, the Company has recognized $38.9 million of collaboration revenue, including $10.3 million in the year ended December 31, 2018, $9.3 million in the year ended December 31, 2017, and $7.8 million in year ended December 31, 2016, in the consolidated statements of operations related to this agreement. As of December 31, 2018, there was approximately $18.5 million of the aggregate transaction price remaining to be recognized, which will be recognized through December 2019.

As of each of the periods ended December 31, 2018 and 2017, the Company had accounts receivable of $6.0 million related to this agreement. As of December 31, 2018 and 2017, the Company had deferred revenue of $14.5 million and $11.2 million, respectively, related to this agreement. Amounts for 2018 are reflective of accounting under ASC 606 and amounts for 2017 are reflective of accounting under ASC 605 and therefore may not be comparable.

Regeneron Pharmaceuticals, Inc.

In April 2016, the Company entered into a license and collaboration agreement with Regeneron (the “Regeneron Agreement”).

Agreement Structure. The Regeneron Agreement has two principal components: i) a product development component under which the parties will research, develop and commercialize CRISPR/Cas-based therapeutic products primarily focused on genome editing in the liver, and ii) a technology collaboration component, pursuant to which the Company and Regeneron will engage in research and development activities aimed at discovering and developing novel technologies and improvements to CRISPR/Cas technology to enhance the Company’s genome editing platform. Under this agreement, the Company also may access the Regeneron Genetics Center and proprietary mouse models to be provided by Regeneron for a limited number of the Company’s liver programs.

Scope of Collaboration. Under the terms of the six-year collaboration, Regeneron may obtain exclusive rights for up to 10 targets to be chosen by Regeneron during the collaboration term, subject to a target selection process and various adjustments and limitations set forth in the agreement. Of these 10 total targets, Regeneron may select up to five non-liver targets, while the remaining targets must be focused in the liver. Certain non-liver targets from the Company’s ongoing and planned research at the time, as well as any targets included in another of the Company’s collaborations, are excluded from this collaboration. At the inception of the agreement, Regeneron selected the first of its 10 targets, transthyretin amyloidosis (“ATTR”), which is subject to a Co-Development and Co-Promotion Agreement (“Co/Co”) between the Company and Regeneron, the general terms and conditions for which were outlined within the Regeneron Agreement.

Research Collaboration. Research activities under the collaboration will be governed by evaluation and research and development plans that will outline the parties’ responsibilities under, anticipated timelines of and budgets for, the various programs. The Company will assist Regeneron with the preliminary evaluation of its selected liver targets, and Regeneron will be responsible for preclinical research and conducting clinical development, manufacturing and commercialization of products directed to each of its exclusive targets. The Company may assist, as requested by Regeneron, with the later discovery and research of product candidates directed to any selected target. For each selected target, Regeneron is required to use commercially reasonable efforts to submit regulatory filings necessary to achieve IND acceptance for at least one product directed to each applicable target, and following IND acceptance for at least one product, to develop and commercialize such product.

Reserved Liver Targets. The Company retains the exclusive right to solely develop products via CRISPR genome editing directed against certain specified genetic targets. During the collaboration term and subject to a target selection process, the Company has the right to choose additional liver targets for its own development using commercially reasonable efforts. Certain targets that either the Company or Regeneron select during the term may be subject to further co-development and co-commercialization arrangements at the Company or Regeneron’s option, as applicable, which either can exercise pursuant to defined conditions.

Governance. The parties formed a joint steering committee (“JSC”), which is responsible for setting research objectives and overseeing the general strategies and activities undertaken by the parties under the Regeneron Agreement. Additionally, the parties formed a Joint Development and Commercialization Committee (“JDCC”) to oversee all profit share products under the Co/Co discussed below. The JDCC will have responsibility for overseeing the development, manufacture, regulatory matters, and commercialization (including pricing and reimbursement) of ATTR, as the first profit share product under the collaboration agreement.

Financial Terms. The Company received a nonrefundable upfront payment of $75.0 million. In addition, on Regeneron programs that are not subject to co-development and co-promotion agreements the Company may be eligible to earn, on a per-licensed target basis, (i) up to $25.0 million in development milestones, including for the dosing of the first patient in each of Phase I, Phase II and Phase III clinical trials, (ii) up to $110.0 million in regulatory milestones, including for the acceptance of a regulatory filing in the U.S., and for obtaining regulatory approval in the U.S. and in certain other identified countries,, and (iii) up to $185.0 million in sales-based milestone payments. The Company is also eligible to earn royalties ranging from the high single digits to low teens, in each case, on a per-product basis, which royalties are potentially subject to various reductions and offsets and incorporate the Company’s existing low- to mid-single-digit royalty obligations under a license agreement with Caribou.

Equity Investments. In connection with this collaboration, Regeneron purchased $50.0 million of the Company’s common stock in a private placement under a Stock Purchase Agreement (the “Stock Purchase Agreement”) concurrent with the Company’s initial public offering.

Term and Termination. The collaboration term ends in April 2022, except that Regeneron may make a one-time payment of $25.0 million to extend the term for an additional two-year period. The agreement will continue until the date when no royalty or other payment obligations are due, unless earlier terminated in accordance with the terms of the agreement. Regeneron’s royalty payment obligations expire on a country-by-country and product-by-product basis upon the later of (i) the expiration of the last valid claim of the royalty-bearing patents covering such product in such country, (ii) 12 years from the first commercial sale of such product in such country, or (iii) the expiration of regulatory exclusivity for such product. The Company may terminate the agreement on a target-by-target basis if Regeneron or any of its affiliates institutes a patent challenge against the Company’s CRISPR/Cas or certain other background patent rights. The Company may also terminate the agreement on a target-by-target basis if Regeneron does not proceed with the development of a product directed to a selected target within specified periods of time. Regeneron may terminate the agreement, without cause, upon 180 days written notice to the Company, either in its entirety or on a target-by-target basis, in which event, certain rights in the terminated targets and associated IP revert to the Company, as described in the agreement. Following such termination, the Company may owe Regeneron royalties, in certain circumstances, up to mid-single digits on any terminated targets that the Company subsequently commercializes on a product-by-product basis for a period of 12 years after the first commercial sale of any such products. Either party may terminate the agreement either in its entirety or with respect to the technology collaboration or one or more of the targets selected by Regeneron, in the event of the other party’s uncured material breach.

Co-Development and Co-Promotion Agreement. In July 2018, the Company and Regeneron finalized the form of the Co/Co that will be used as the basis for each Co/Co agreement directed to a target. Simultaneously, the Company and Regeneron executed the Co/Co agreement directed to the first collaboration target, ATTR, for which the Company will be the clinical and commercial Lead Party (see below). As such, Regeneron will be the Participating Party (see below), and will share equally in worldwide development costs and profits as long as it funds half of the defined research and development costs attributable to the ATTR program.

Co-Development and Co-Promotion: Agreement Structure Under the Co/Co Agreement, Regeneron has the right to exercise up to at least five Co/Co options on the Company’s liver targets (other than the Company’s reserved liver targets), while the Company may exercise at least one Co/Co option on Regeneron’s liver targets, the exact number of Co/Co options being subject to certain conditions of the target selection process. Co/Co options must be exercised (or forfeited) once a target reaches a defined preclinical stage. Within 15 days of exercising the Co/Co option, the party exercising the option must pay $1.5 million to the other party as compensation for prior work. The ATTR program was exempted from this payment. One Party will be the “Lead Party” and the other Party the “Participating Party”. The Lead Party shall have control and primary responsibility for the development, manufacturing, regulatory and commercial activities. The Participating Party shall have the right to consult on these activities through its participation on the JDCC and will have the right to co-fund development and commercialization activities in exchange for a share of profits. In general, the parties will share equally in worldwide development costs and profits of any future products. Prior to reaching a specific development milestone, the Participating Party may elect to reduce its share of worldwide development costs and profits by 50.0 percent

Co-Development and Co-Promotion: Termination. Either party may terminate by providing 180 days written notice. If the Company terminates, the product becomes a Regeneron product, and is subject to all future milestone and royalty payment obligations under the Regeneron agreement. If Regeneron terminates and has contributed at least $5 million in development costs, the Company will pay low- to mid- single digit royalties on the net sales of the product, depending on co-funding percentage, stage at termination, if any, and Regeneron IP incorporated into the product.

Accounting Analysis. The Company determined that the Regeneron Agreement is within the scope of ASC 606. The Company evaluated the promised goods and services under the Regeneron Agreement and determined that the Regeneron Agreement included three performance obligations: (1) a combined performance obligation including the licenses to targets and the associated research activities and evaluation plans; (2) a combined performance obligation including the technology collaboration and associated research activities; and (3) the common stock.

The Company also concluded that the ATTR Co/Co meets the definition of a collaborative arrangement per ASC 808, which is outside of the scope of ASC 606. Since ASC 808 does not provide recognition and measurement guidance for collaborative arrangements, the Company has analogized to ASC 606. As such, the Company classifies payments received or made under the cost sharing provisions of the ATTR Co/Co as a component of revenues in the consolidated statements of operations.

Under the Regeneron Agreement, the Company determined that the transaction price was $125.0 million, consisting of the following consideration: (1) the nonrefundable upfront payment of $75.0 million; and (2) the payment for the common stock of $50.0 million. None of the clinical or regulatory milestones were included in the transaction price, as all milestone amounts were fully constrained. As part its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future regulatory progress and the licensee’s efforts. Any consideration related to sales-based milestones and royalties will be recognized when the related sales occur as they were determined to relate predominantly to the licenses granted to Regeneron and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and when events whose outcome are resolved or other changes in circumstances occur.

The Company first allocated $50.0 million of the transaction price to the common stock. The common stock was sold at its standalone selling price and the Company concluded that the total discount inherent in the arrangement is entirely attributable to the combined performance obligation including the licenses to targets and associated research activities and evaluation plans and the combined performance obligation including the technology collaboration and associated research activities. As such, the remaining $75.0 million of the transaction price was allocated to the combined performance obligation including the licenses to targets and associated research activities and evaluation plans and the combined performance obligation including the technology collaboration and associated research activities on a relative standalone selling price basis. The Company estimated the standalone selling price of each combined performance obligation by taking into consideration internal estimates of research and development personnel needed to perform the research and development services, estimates of expected cash outflows to third parties for services and supplies, selling prices of comparable transactions and typical gross profit margins. As a result of this evaluation, the Company allocated $63.8 million to the combined performance obligation including the licenses to targets and associated research activities and evaluation plans and $11.2 million to the combined performance obligation including the technology collaboration and associated research activities. The $63.8 million allocated to the combined performance obligation including the licenses to targets and associated research activities and evaluation plans is being recognized on a straight-line basis over the six-year performance period of the arrangement, which, in management’s judgment, is the best measure of progress towards satisfying the performance obligation and represents the Company’s best estimate of the period of the obligation. The $11.2 million allocated to the combined performance obligation including the technology collaboration and associated research activities is being recognized on a straight-line basis over a period beginning with the inception of the technology collaboration in September 2016 through the end of the arrangement, which, in management’s judgment, is the best measure of progress towards satisfying the performance obligation and represents the Company’s best estimate of the period of the obligation.

Revenue Recognition – Collaboration Revenue. Through December 31, 2018, excluding the amounts allocated to Regeneron’s purchase of common stock, the Company recorded a $75.0 million upfront payment and $12.1 million for research and development services under the Regeneron Arrangement. Through December 31, 2018, the Company has recognized $45.6 million, including $20.1 million, $16.8 million and $8.7 million of collaboration revenue in the years ended December 31, 2018, 2017 and 2016, respectively, in the consolidated statements of operations related to this arrangement. This includes $7.5 million, $4.1 million, and $0.5 million representing payments due from Regeneron pursuant to the ATTR Co/Co, which is accounted for under ASC 808. As of December 31, 2018, there was approximately $41.4 million of the aggregate transaction price remaining to be recognized, which will be recognized ratably through April 2022. As of December 31, 2018 and 2017, the Company had deferred revenue of $41.4 million and $54.1 million, respectively, and accounts receivable of $1.5 million and $4.5 million, respectively, related to this arrangement.

Equity-Based Compensation

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity-Based Compensation

8. Equity-Based Compensation

Equity-based compensation expense is classified in the consolidated statements of operations as follows:

	Year Ended December 31,
	2018		2017		2016
	(In thousands)
Research and development	$	8,994	$	7,280	$	4,083
General and administrative		8,052		8,042		2,632
Total	$	17,046	$	15,322	$	6,715

Restricted Stock

Restricted stock is measured at fair value based on the quoted price of the Company’s common stock.

The following table summarizes the Company’s restricted stock activity for the year ended December 31, 2018:

	Number of Shares			Weighted Average Grant Date Fair Value per Share
Unvested restricted stock as of December 31, 2017		479,822		$	0.90
Granted		86,250			22.98
Vested		(411,372	)		0.83
Cancelled		(45,627	)		8.31
Unvested restricted stock as of December 31, 2018		109,073		$	15.53

As of December 31, 2018, there was $1.4 million of unrecognized equity-based compensation expense related to restricted stock that is expected to vest. These costs are expected to be recognized over a weighted average remaining vesting period of 1.6 years.

Stock Options

The weighted average grant date fair value of options, estimated as of the grant date using the Black-Scholes option pricing model, was $15.05 per option for options granted during the year ended December 31, 2018, $12.43 per option for options granted during the year ended December 31, 2017 and $6.48 per option for options granted during the year ended December 31, 2016. Key assumptions used to apply this pricing model were as follows:

	Year Ended December 31,
	2018			2017			2016
Risk-free interest rate		2.7	%		2.0	%		1.3	%
Expected life of options	6.0 years			6.0 years			6.0 years
Expected volatility of underlying stock		87.1	%		93.9	%		88.0	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

The following is a summary of stock option activity for the year ended December 31, 2018:

	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(In years)		(In thousands)
Outstanding at December 31, 2017		4,705,448		$	12.09
Granted		2,128,126			20.38
Exercised		(1,142,944	)		9.32
Forfeited		(652,967	)		16.59
Outstanding at December 31, 2018		5,037,663		$	15.63		8.38	$	8,940
Exercisable at December 31, 2018		1,736,487		$	11.42		7.34	$	6,360

As of December 31, 2018, there was $38.2 million of unrecognized compensation cost related to stock options that are expected to vest. These costs are expected to be recognized over a weighted average remaining vesting period of 2.9 years.

Loss Per Share

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Loss Per Share

9. Loss Per Share

Basic and diluted loss per share was calculated as follows:

	Year Ended December 31,
	2018			2017			2016
	(In thousands)
Net loss	$	(85,343	)	$	(67,543	)	$	(31,634	)
Weighted average shares outstanding, basic and diluted		43,069			36,006			22,222
Net loss per share, basic and diluted	$	(1.98	)	$	(1.88	)	$	(1.42	)

The following common stock equivalents were excluded from the calculation of diluted loss per share in 2018, 2017 and 2016 because their inclusion would have been anti-dilutive:

	Year Ended December 31,
	2018		2017		2016
	(In thousands)
Unvested restricted stock		109		480		1,362
Stock options		5,038		4,705		3,040
		5,147		5,185		4,402

Stockholders’ Equity

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Stockholders’ Equity

10. Stockholders’ Equity

On May 11, 2016, the Company completed an initial public offering (“IPO”) of its common stock, which resulted in the sale of 6,900,000 shares, including all additional shares available to cover over-allotments, at a price of $18.00 per share. The Company received net proceeds before expenses from the IPO of $115.5 million after deducting underwriting discounts and commissions paid by the Company. In preparation for the IPO, the Company’s board of directors and stockholders approved a one-for-1.7 reverse stock split of the Company’s common stock effective April 25, 2016. All share and per share amounts in the consolidated financial statements and notes thereto have been retroactively adjusted, where necessary, to give effect to this reverse stock split. In connection with the closing of the IPO, all of the Company’s outstanding convertible preferred stock automatically converted to common stock at a one-for-0.6465903 ratio as of May 11, 2016, resulting in an additional 23,481,956 shares of common stock of the Company becoming outstanding. In addition, the Company issued a total of 3,055,554 shares of common stock for $55.0 million in two separate, concurrent private placements upon the closing of the IPO.

On November 1, 2017, the Company entered into an underwriting agreement related to a public offering of 6,250,000 shares of the Company’s common stock, par value $0.0001 per share. The offering closed on November 6th and the Company received net proceeds of $141.0 million, after deducting underwriting discounts.

On October 12, 2018, the Company filed a Registration Statement on Form S-3 (the “Shelf”) with the SEC in relation to the registration of common stock, preferred stock, warrants and/or units of any combination thereof (collectively, the “Securities”). The Company also simultaneously entered into an Open Market Sale Agreement (the “Sales Agreement”) with Jefferies LLC, (the “Sales Agent”), to provide for the offering, issuance and sale by the Company of up to an aggregate amount of $100.0 million of its common stock from time to time in “at-the-market” offerings under the Shelf and subject to the limitations thereof. On November 15, 2018, the Company issued 1,659,300 shares of its common stock in accordance with the Sales Agreement for net proceeds of $29.0 million, after payment of cash commissions of 3.0 percent of the gross proceeds to the Sales Agent. Additionally, the Company incurred approximately $0.4 million related to legal, accounting and other fees in connection with the Sales Agreement and subsequent sale.

The Company classifies stock that is redeemable in circumstances outside of the Company’s control outside of permanent equity. The Company recorded convertible preferred stock at fair value upon issuance, net of any issuance costs or discounts. No accretion was recognized as the contingent events that could give rise to redemption were not deemed probable. The preferred stock outstanding at December 31, 2015 was automatically converted to common stock in connection with the closing of the IPO.

Related Party Transactions

12 Months Ended

Dec. 31, 2018

Related Party Transactions

11. Related Party Transactions

Caribou Biosciences

In July 2014, the Company licensed from Caribou certain IP and entered into an arrangement under which Caribou provided research and development services. In addition, under the license agreement the Company agreed to pay 30 percent of Caribou’s patent prosecution, filing and maintenance costs under its IP license agreement with Caribou. Caribou owned 5.5 percent of the Company’s voting interests as of December 31, 2018.

On October 17, 2018, the Company initiated an arbitration proceeding with JAMS against Caribou asserting that Caribou is violating the terms and conditions of the license agreement, as well as other contractual and legal rights, by using and seeking to license to third parties two patent families relating to specific structural or chemical modifications of guide RNAs, that were purportedly invented or controlled by Caribou, in the Company’s exclusive human therapeutic field. Caribou has asserted that the two families of IP are outside the scope of the license agreement. In accordance with the Caribou License, the Company has submitted a demand for arbitration seeking a declaration that the disputed IP is included within the scope of the Company’s license under the Caribou License, an award of compensatory, consequential and punitive damages based on Caribou’s conduct, and an injunction prohibiting Caribou from licensing or using this IP in the Company’s exclusive human therapeutics field, among other claims. The arbitration will take place in San Francisco, California.

The Company recognized general and administrative expense of $0.9 million, $0.5 million and $0.9 million during the years ended December 31, 2018, 2017 and 2016 related to the Company’s obligation to pay 30.0 percent of Caribou’s patent defense costs. Additionally, during the year ended December 31, 2016 the Company recognized research and development expense of $1.3 million related to license and service agreements entered into with Caribou.

Novartis Institutes for Biomedical Research

In connection with its entry into the collaboration and license agreement and related equity transactions with Novartis, in 2015 the Company issued Novartis capital stock, and in May 2016, Novartis acquired 277,777 shares of the Company’s common stock in a private placement transaction concurrent with the Company’s IPO. As a result of these capital stock transactions, Novartis collectively owned 9.6 percent of the Company’s voting interests as of December 31, 2018. Refer to Note 7 for additional information regarding this collaboration agreement.

The Company recognized collaboration revenue of $10.3 million, $9.3 million and $7.8 million in the years ended December 31, 2018, 2017 and 2016, respectively, related to this agreement. As of each of the periods ended December 31, 2018 and 2017, the Company had recorded accounts receivable of $6.0 million related to this collaboration. As of the periods ended December 31, 2018 and 2017, the Company had deferred revenue of $14.5 million and $11.2 million, respectively, related to this collaboration.

401(k) Plan

12 Months Ended

Dec. 31, 2018

Defined Benefit Pension Plans And Defined Benefit Postretirement Plans Disclosure [Abstract]

401(k) Plan

12. 401(k) Plan

In 2015, the Company established the Intellia Therapeutics, Inc. 401(k) Plan (the “401(k) Plan”) for its employees, which is designed to be qualified under Section 401(k) of the Internal Revenue Code. Eligible employees are permitted to contribute to the 401(k) Plan within statutory and 401(k) Plan limits. During 2018, the Company began to make matching contributions of 50 percent of the first 6 percent of employee contributions. The Company made matching contributions of $0.6 million for the year ended December 31, 2018.

Unaudited Quarterly Results

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Unaudited Quarterly Results

13. Unaudited Quarterly Results

The results of operations on a quarterly basis for the years ended December 31, 2018 and 2017 are set forth below:

	March 31, 2018			June 30, 2018			September 30, 2018			December 31, 2018
	(Amounts in thousands except per share data)
Collaboration revenue	$	7,469		$	7,677		$	7,408		$	7,880
Operating expenses:
Research and development		22,493			23,467			23,237			19,918
General and administrative		7,406			7,805			8,270			8,708
Total operating expenses		29,899			31,272			31,507			28,626
Operating loss		(22,430	)		(23,595	)		(24,099	)		(20,746	)
Interest income		1,074			1,376			1,397			1,680
Net loss	$	(21,356	)	$	(22,219	)	$	(22,702	)	$	(19,066	)
Net loss per share, basic and diluted	$	(0.51	)	$	(0.52	)	$	(0.53	)	$	(0.43	)
Weighted average shares outstanding, basic and diluted		42,043			42,836			43,161			44,215

	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
	(Amounts in thousands except per share data)
Collaboration revenue	$	6,215		$	5,917		$	7,317		$	6,668
Operating expenses:
Research and development		13,431			15,565			17,481			21,170
General and administrative		5,732			6,369			5,711			10,213
Total operating expenses		19,163			21,934			23,192			31,383
Operating loss		(12,948	)		(16,017	)		(15,875	)		(24,715	)
Interest income		317			424			519			752
Net loss	$	(12,631	)	$	(15,593	)	$	(15,356	)	$	(23,963	)
Net loss per share, basic and diluted	$	(0.36	)	$	(0.45	)	$	(0.44	)	$	(0.61	)
Weighted average shares outstanding, basic and diluted		34,723			34,916			35,189			39,155

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Fair Value Measurements

	Fair Value as of December 31, 2018
	Total		Level 1		Level 2		Level 3
	(In thousands)
Cash equivalents	$	45,986	$	45,986	$	-	$	-
Marketable securities		255,203		165,948		89,255		-
Total	$	301,189	$	211,934	$	89,255	$	-

	Fair Value as of December 31, 2017
	Total		Level 1		Level 2		Level 3
	(In thousands)
Cash equivalents	$	330,896	$	330,896	$	-	$	-
Total	$	330,896	$	330,896	$	-	$	-

Other financial instruments, including accounts receivable and accounts payable, are carried at cost, which approximate fair value due to the short duration and term to maturity.

Cash Equivalents

Marketable Securities

The following table summarizes the Company’s available-for-sale marketable securities as of December 31, 2018 at net book value:

	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(In thousands)
Short-term marketable securities:
U.S. Treasury securities	$	165,959	$	2	$	(13	)	$	165,948
Financial institution debt securities		65,436		1		(17	)		65,420
Corporate debt securities		23,836		-		(1	)		23,835
Total	$	255,231	$	3	$	(31	)	$	255,203

Concentrations of Credit Risk

Property and Equipment

The Company records property and equipment at cost and recognizes depreciation and amortization using the straight-line method over the following estimated useful lives of the respective assets:

Asset Category		Useful Life
Laboratory equipment		5 years
Office furniture and equipment		5 years
Computer software		3 years
Computer equipment		3 years
Leasehold improvements		5 years or term of respective lease, if shorter

Impairment of Long-Lived Assets

Income Taxes

Revenue Recognition

The following table presents changes in the Company’s contract liabilities during the year ended December 31, 2018 (in thousands):

	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
Year Ended December 31, 2018
Contract liabilities:
Deferred revenue	$	59,868	$	19,000	$	(22,936	)	$	55,932

During the year ended December 31, 2018, the Company recognized the following revenues as a result of changes in the contract liability balance (in thousands):

Revenue recognized in the period from:

Year Ended

December 31, 2018

Amounts included in the contract liability at the beginning of the period

22,936

Costs to obtain and fulfill a contract

Research and Development Expenses

Equity-Based Compensation

(Loss) Earnings per Share

Segment Information

Recent Accounting Pronouncements

Impact of Adoption


Consolidated Balance Sheet	January 1, 2018 (in thousands)
	Pre-Adoption			ASC 606 Adjustment			Post-Adoption
Current portion of deferred revenue	$	21,188		$	(2,769	)	$	18,419
Deferred revenue, net of current portion		44,111			(2,662	)		41,449
Accumulated deficit		(121,113	)		5,431			(115,682	)


	Year Ended December 31, 2018
	Impact of changes in accounting policies
	As Reported			Balances without adoption of ASC 606			Effect of Change Higher/(Lower)
Collaboration revenue	$	30,434		$	31,838		$	(1,404	)
Operating loss		(90,870	)		(89,466	)		(1,404	)
Net loss	$	(85,343	)	$	(83,939	)	$	(1,404	)
Net loss per share, basic and diluted	$	(1.98	)	$	(1.95	)	$	(0.03	)

	December 31, 2018
	Impact of changes in accounting policies
	As Reported			Balances without adoption of ASC 606			Effect of Change Higher/(Lower)
Liabilities:
Deferred revenue – current	$	27,122		$	31,149		$	(4,027	)
Deferred revenue – noncurrent		28,810			28,810			-
Stockholders' equity:
Accumulated deficit	$	(201,025	)	$	(205,052	)	$	4,027

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Financial Assets Recognized at Fair Value on Recurring Basis

As of December 31, 2018 and 2017, the Company’s financial assets recognized at fair value on a recurring basis consisted of the following:

	Fair Value as of December 31, 2018
	Total		Level 1		Level 2		Level 3
	(In thousands)
Cash equivalents	$	45,986	$	45,986	$	-	$	-
Marketable securities		255,203		165,948		89,255		-
Total	$	301,189	$	211,934	$	89,255	$	-

	Fair Value as of December 31, 2017
	Total		Level 1		Level 2		Level 3
	(In thousands)
Cash equivalents	$	330,896	$	330,896	$	-	$	-
Total	$	330,896	$	330,896	$	-	$	-

Summary of Available-for-sale Marketable Securities

The following table summarizes the Company’s available-for-sale marketable securities as of December 31, 2018 at net book value:

	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(In thousands)
Short-term marketable securities:
U.S. Treasury securities	$	165,959	$	2	$	(13	)	$	165,948
Financial institution debt securities		65,436		1		(17	)		65,420
Corporate debt securities		23,836		-		(1	)		23,835
Total	$	255,231	$	3	$	(31	)	$	255,203

Summary of Property and Equipment at Cost and Recognizes Depreciation and Amortization Using the Straight-Line Method Over Estimated Useful Lives

The Company records property and equipment at cost and recognizes depreciation and amortization using the straight-line method over the following estimated useful lives of the respective assets:

Asset Category		Useful Life
Laboratory equipment		5 years
Office furniture and equipment		5 years
Computer software		3 years
Computer equipment		3 years
Leasehold improvements		5 years or term of respective lease, if shorter

Summary of Changes in Contract Liabilities

The following table presents changes in the Company’s contract liabilities during the year ended December 31, 2018 (in thousands):

	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
Year Ended December 31, 2018
Contract liabilities:
Deferred revenue	$	59,868	$	19,000	$	(22,936	)	$	55,932

Summary of Revenues Recognized Resulting From Changes in Contract Liability Balance

During the year ended December 31, 2018, the Company recognized the following revenues as a result of changes in the contract liability balance (in thousands):

Revenue recognized in the period from:

Year Ended

December 31, 2018

Amounts included in the contract liability at the beginning of the period

22,936

Schedule of Adjustments to Consolidated Balance Sheet Due to Adoption of New Guidance

As a result of applying the modified retrospective method to adopt the new guidance, the following adjustments were made to accounts on the consolidated balance sheet as of January 1, 2018:


Consolidated Balance Sheet	January 1, 2018 (in thousands)
	Pre-Adoption			ASC 606 Adjustment			Post-Adoption
Current portion of deferred revenue	$	21,188		$	(2,769	)	$	18,419
Deferred revenue, net of current portion		44,111			(2,662	)		41,449
Accumulated deficit		(121,113	)		5,431			(115,682	)

Summary of Impact of Adoption to Consolidated Statement of Operations and Balance Sheet


	Year Ended December 31, 2018
	Impact of changes in accounting policies
	As Reported			Balances without adoption of ASC 606			Effect of Change Higher/(Lower)
Collaboration revenue	$	30,434		$	31,838		$	(1,404	)
Operating loss		(90,870	)		(89,466	)		(1,404	)
Net loss	$	(85,343	)	$	(83,939	)	$	(1,404	)
Net loss per share, basic and diluted	$	(1.98	)	$	(1.95	)	$	(0.03	)

	December 31, 2018
	Impact of changes in accounting policies
	As Reported			Balances without adoption of ASC 606			Effect of Change Higher/(Lower)
Liabilities:
Deferred revenue – current	$	27,122		$	31,149		$	(4,027	)
Deferred revenue – noncurrent		28,810			28,810			-
Stockholders' equity:
Accumulated deficit	$	(201,025	)	$	(205,052	)	$	4,027

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2018

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment, net consisted of the following:

	December 31,
	2018			2017
	(in thousands)
Laboratory equipment	$	22,453		$	16,704
Office furniture and equipment	960			960
Computer equipment	929			845
Leasehold improvements	898			656
Computer software	433			436
Total property and equipment		25,673			19,601
Less: accumulated depreciation and amortization		(8,612	)		(4,329	)
Property and equipment, net	$	17,061		$	15,272

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2018

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following:

	December 31, 2018		December 31, 2017
	(In thousands)
Employee compensation and benefits	$	6,175	$	4,773
Accrued research and development		2,328		1,960
Accrued legal and professional expenses		1,633		587
Accrued other		606		679
Total accrued expenses	$	10,742	$	7,999

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of the Federal Statutory Income Tax Rate and the Company's Effective Income Tax Rate

A reconciliation of the federal statutory income tax rate and the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2018			2017			2016
Federal statutory income tax rate		(21.0	)%		(34.0	)%		(34.0	)%
State income taxes		(8.6	)		(6.9	)		(6.7	)
Research and development tax credits		(4.7	)		(3.4	)		(2.8	)
Stock-based compensation		(0.6	)		3.6			1.9
Change in U.S. tax rate		-			18.7			-
Change in valuation allowance		34.9			22.0			41.6
Effective income tax rate		-	%		-	%		-	%

Summary of Company's Net Deferred Tax Assets (Liabilities)

The Company’s net deferred tax assets (liabilities) consisted of the following:

	December 31,
	2018			2017
	(in thousands)
Deferred tax assets:
Intangibles, including acquired in-process research and development	$	1,201		$	1,303
Capitalized start-up costs		463			502
Net operating loss carryforwards		34,234			9,406
Research and development credit carryforwards		11,766			5,817
Deferred revenue		12,199			15,913
Equity-based compensation		4,064			3,248
Accruals and allowances		1,359			1,112
Gross deferred tax assets		65,286			37,301
Deferred tax asset valuation allowance		(64,046	)		(35,372	)
Total deferred tax assets		1,240			1,929
Deferred tax liabilities:
Fixed assets		(1,240	)		(1,929	)
Total deferred tax liabilities		(1,240	)		(1,929	)
Net deferred tax asset (liability)	$	-		$	-

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments

Future minimum lease payments under the Company’s property leases as of December 31, 2018 are as follows:

Year Ending December 31,	(In thousands)
2019	$	5,616
2020		4,963
2021		5,507
2022		3,861
Thereafter		-
	$	19,947

Equity-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Equity-Based Compensation Expense

Equity-based compensation expense is classified in the consolidated statements of operations as follows:

	Year Ended December 31,
	2018		2017		2016
	(In thousands)
Research and development	$	8,994	$	7,280	$	4,083
General and administrative		8,052		8,042		2,632
Total	$	17,046	$	15,322	$	6,715

Summary of Restricted Stock Activity

The following table summarizes the Company’s restricted stock activity for the year ended December 31, 2018:

	Number of Shares			Weighted Average Grant Date Fair Value per Share
Unvested restricted stock as of December 31, 2017		479,822		$	0.90
Granted		86,250			22.98
Vested		(411,372	)		0.83
Cancelled		(45,627	)		8.31
Unvested restricted stock as of December 31, 2018		109,073		$	15.53

Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted

Key assumptions used to apply this pricing model were as follows:

	Year Ended December 31,
	2018			2017			2016
Risk-free interest rate		2.7	%		2.0	%		1.3	%
Expected life of options	6.0 years			6.0 years			6.0 years
Expected volatility of underlying stock		87.1	%		93.9	%		88.0	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

Summary of Stock Option Activity

The following is a summary of stock option activity for the year ended December 31, 2018:

	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(In years)		(In thousands)
Outstanding at December 31, 2017		4,705,448		$	12.09
Granted		2,128,126			20.38
Exercised		(1,142,944	)		9.32
Forfeited		(652,967	)		16.59
Outstanding at December 31, 2018		5,037,663		$	15.63		8.38	$	8,940
Exercisable at December 31, 2018		1,736,487		$	11.42		7.34	$	6,360

Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Net Loss Per Share

Basic and diluted loss per share was calculated as follows:

	Year Ended December 31,
	2018			2017			2016
	(In thousands)
Net loss	$	(85,343	)	$	(67,543	)	$	(31,634	)
Weighted average shares outstanding, basic and diluted		43,069			36,006			22,222
Net loss per share, basic and diluted	$	(1.98	)	$	(1.88	)	$	(1.42	)

Potential Dilutive Securities Excluded from Computation of Diluted Net Loss Per Common Share

The following common stock equivalents were excluded from the calculation of diluted loss per share in 2018, 2017 and 2016 because their inclusion would have been anti-dilutive:

	Year Ended December 31,
	2018		2017		2016
	(In thousands)
Unvested restricted stock		109		480		1,362
Stock options		5,038		4,705		3,040
		5,147		5,185		4,402

Unaudited Quarterly Results (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Schedule of Results of Operations on Quarterly Basis

The results of operations on a quarterly basis for the years ended December 31, 2018 and 2017 are set forth below:

	March 31, 2018			June 30, 2018			September 30, 2018			December 31, 2018
	(Amounts in thousands except per share data)
Collaboration revenue	$	7,469		$	7,677		$	7,408		$	7,880
Operating expenses:
Research and development		22,493			23,467			23,237			19,918
General and administrative		7,406			7,805			8,270			8,708
Total operating expenses		29,899			31,272			31,507			28,626
Operating loss		(22,430	)		(23,595	)		(24,099	)		(20,746	)
Interest income		1,074			1,376			1,397			1,680
Net loss	$	(21,356	)	$	(22,219	)	$	(22,702	)	$	(19,066	)
Net loss per share, basic and diluted	$	(0.51	)	$	(0.52	)	$	(0.53	)	$	(0.43	)
Weighted average shares outstanding, basic and diluted		42,043			42,836			43,161			44,215

	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
	(Amounts in thousands except per share data)
Collaboration revenue	$	6,215		$	5,917		$	7,317		$	6,668
Operating expenses:
Research and development		13,431			15,565			17,481			21,170
General and administrative		5,732			6,369			5,711			10,213
Total operating expenses		19,163			21,934			23,192			31,383
Operating loss		(12,948	)		(16,017	)		(15,875	)		(24,715	)
Interest income		317			424			519			752
Net loss	$	(12,631	)	$	(15,593	)	$	(15,356	)	$	(23,963	)
Net loss per share, basic and diluted	$	(0.36	)	$	(0.45	)	$	(0.44	)	$	(0.61	)
Weighted average shares outstanding, basic and diluted		34,723			34,916			35,189			39,155

Summary of Significant Accounting Policies - Summary of Financial Assets Recognized at Fair Value on Recurring Basis (Detail) - Fair Value on Recurring Basis [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 45,986	$ 330,896
Marketable securities	255,203
Total	301,189	330,896
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	45,986	330,896
Marketable securities	165,948
Total	211,934	$ 330,896
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	89,255
Total	$ 89,255

Summary of Significant Accounting Policies - Summary of Available -for-sale Marketable Securities (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Marketable Securities [Line Items]
Amortized Cost	$ 255,231
Gross Unrealized Gains	3
Gross Unrealized Losses	(31)
Estimated Fair Value	255,203
U.S. Treasury Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	165,959
Gross Unrealized Gains	2
Gross Unrealized Losses	(13)
Estimated Fair Value	165,948
Financial Institution Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	65,436
Gross Unrealized Gains	1
Gross Unrealized Losses	(17)
Estimated Fair Value	65,420
Corporate Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	23,836
Gross Unrealized Losses	(1)
Estimated Fair Value	$ 23,835

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) Segment	Jan. 01, 2019 USD ($)	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Realized loss on marketable securities	$ 0
Marketable securities	$ 255,203,000		$ 0
Percentage of likelihood of realization required to record tax benefit	50.00%
Expenses incurred to obtain collaboration agreements and costs to fulfill contracts	$ 0
Costs to obtain or fulfill contract capitalized	$ 0
Number of reportable segment \| Segment	1
Maximum [Member] \| ASU 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Maximum lease term	12 months
Maximum [Member] \| ASU 2016-02 [Member] \| Subsequent Event [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating lease, liability		$ 21,000,000
Operating lease, right-of-use asset		23,000,000
Minimum [Member] \| ASU 2016-02 [Member] \| Subsequent Event [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating lease, liability		19,000,000
Operating lease, right-of-use asset		$ 21,000,000

Summary of Significant Accounting Policies - Summary of Property and Equipment at Cost and Recognizes Depreciation and Amortization Using the Straight-Line Method Over Estimated Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2018
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Office Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Computer Software [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years or term of respective lease, if shorter

Summary of Significant Accounting Policies - Summary of Changes in Contract Liabilities (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Contract liabilities:
Deferred revenue, Balance at Beginning of Period	$ 59,868
Deferred revenue, Additions	19,000
Deferred revenue, Deductions	(22,936)
Deferred revenue, Balance at End of Period	$ 55,932

Summary of Significant Accounting Policies - Summary of Revenues Recognized Resulting From Changes in Contract Liability Balance (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Revenue From Contract With Customer [Abstract]
Amounts included in the contract liability at the beginning of the period	$ 22,936

Summary of Significant Accounting Policies - Schedule of Adjustments to Consolidated Balance Sheet Due to Adoption of New Guidance (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Item Effected [Line Items]
Current portion of deferred revenue	$ 27,122		$ 21,188
Deferred revenue, net of current portion	28,810		44,111
Accumulated deficit	(201,025)		$ (121,113)
Accounting Standards Update (“ASU”) No. 2014-09 [Member]
Item Effected [Line Items]
Current portion of deferred revenue		$ 18,419
Deferred revenue, net of current portion		41,449
Accumulated deficit		(115,682)
Accounting Standards Update (“ASU”) No. 2014-09 [Member] \| ASC 606 Adjustment [Member]
Item Effected [Line Items]
Current portion of deferred revenue	(4,027)	(2,769)
Deferred revenue, net of current portion		(2,662)
Accumulated deficit	$ 4,027	$ 5,431

Summary of Significant Accounting Policies - Summary of Impact of Adoption to Consolidated Statement of Operations and Balance Sheet (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue	$ 7,880	$ 7,408	$ 7,677	$ 7,469	$ 6,668	$ 7,317	$ 5,917	$ 6,215	$ 30,434	$ 26,117	$ 16,479
Type of Revenue [Extensible List]									us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating loss	(20,746)	(24,099)	(23,595)	(22,430)	(24,715)	(15,875)	(16,017)	(12,948)	$ (90,870)	$ (69,555)	$ (32,159)
Net loss	$ (19,066)	$ (22,702)	$ (22,219)	$ (21,356)	$ (23,963)	$ (15,356)	$ (15,593)	$ (12,631)	$ (85,343)	$ (67,543)	$ (31,634)
Net loss per share, basic and diluted	$ (0.43)	$ (0.53)	$ (0.52)	$ (0.51)	$ (0.61)	$ (0.44)	$ (0.45)	$ (0.36)	$ (1.98)	$ (1.88)	$ (1.42)
Liabilities:
Deferred revenue – current	$ 27,122				$ 21,188				$ 27,122	$ 21,188
Deferred revenue – noncurrent	28,810				44,111				28,810	44,111
Stockholders’ Equity:
Accumulated deficit	(201,025)				$ (121,113)				(201,025)	$ (121,113)
Accounting Standards Update (“ASU”) No. 2014-09 [Member]
Liabilities:
Deferred revenue – current												$ 18,419
Deferred revenue – noncurrent												41,449
Stockholders’ Equity:
Accumulated deficit												(115,682)
Accounting Standards Update (“ASU”) No. 2014-09 [Member] \| Balances without Adoption of ASC 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue									$ 31,838
Type of Revenue [Extensible List]									us-gaap:LicenseAndServiceMember
Operating loss									$ (89,466)
Net loss									$ (83,939)
Net loss per share, basic and diluted									$ (1.95)
Liabilities:
Deferred revenue – current	31,149								$ 31,149
Deferred revenue – noncurrent	28,810								28,810
Stockholders’ Equity:
Accumulated deficit	(205,052)								(205,052)
Accounting Standards Update (“ASU”) No. 2014-09 [Member] \| Effect of Change Higher/(Lower) [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue									$ (1,404)
Type of Revenue [Extensible List]									us-gaap:LicenseAndServiceMember
Operating loss									$ (1,404)
Net loss									$ (1,404)
Net loss per share, basic and diluted									$ (0.03)
Liabilities:
Deferred revenue – current	(4,027)								$ (4,027)			(2,769)
Deferred revenue – noncurrent												(2,662)
Stockholders’ Equity:
Accumulated deficit	$ 4,027								$ 4,027			$ 5,431

Property and Equipment, net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 25,673	$ 19,601
Less: accumulated depreciation and amortization	(8,612)	(4,329)
Property and equipment, net	17,061	15,272
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	22,453	16,704
Office Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	960	960
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	929	845
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	898	656
Computer Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 433	$ 436

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 4,464	$ 2,994	$ 1,104

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Employee compensation and benefits	$ 6,175	$ 4,773
Accrued research and development	2,328	1,960
Accrued legal and professional expenses	1,633	587
Accrued other	606	679
Total accrued expenses	$ 10,742	$ 7,999

Income Taxes - Schedule of Reconciliation of the Federal Statutory Income Tax Rate and the Company's Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(21.00%)	(34.00%)	(34.00%)
State income taxes	(8.60%)	(6.90%)	(6.70%)
Research and development tax credits	(4.70%)	(3.40%)	(2.80%)
Stock-based compensation	(0.60%)	3.60%	1.90%
Change in U.S. tax rate		18.70%
Change in valuation allowance	34.90%	22.00%	41.60%

Income Taxes - Summary of Company's Net Deferred Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Intangibles, including acquired in-process research and development	$ 1,201	$ 1,303
Capitalized start-up costs	463	502
Net operating loss carryforwards	34,234	9,406
Research and development credit carryforwards	11,766	5,817
Deferred revenue	12,199	15,913
Equity-based compensation	4,064	3,248
Accruals and allowances	1,359	1,112
Gross deferred tax assets	65,286	37,301
Deferred tax asset valuation allowance	(64,046)	(35,372)
Total deferred tax assets	1,240	1,929
Deferred tax liabilities:
Fixed assets	(1,240)	(1,929)
Total deferred tax liabilities	$ (1,240)	$ (1,929)

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Benefit [Line Items]
Net operating loss carryforwards, federal	$ 128,200,000
Net operating loss carryforwards, state	$ 117,000,000
Net operating loss carryforwards, expiration year	2034
Net operating loss carryforwards, expiration date description	Begin to expire in 2034
Research and development tax credit	$ 11,766,000	$ 5,817,000
Research and development tax credits, expiration date description	Begin to expire in 2034 and 2029
Increase in valuation allowance	$ 28,700,000	$ 14,800,000	$ 13,100,000
Unrecognized tax benefits	$ 0
U.S. corporate income tax rate	21.00%	34.00%	34.00%
Provisional amount for decrease in net deferred tax assets offset by decrease in valuation allowance due to remeasurement		$ 12,600,000
Maximum [Member]
Income Tax Benefit [Line Items]
U.S. corporate income tax rate		35.00%
Measurement period		1 year
Federal [Member]
Income Tax Benefit [Line Items]
Research and development tax credit	$ 7,500,000
Research and development tax credits, expiration year	2034
State [Member]
Income Tax Benefit [Line Items]
Research and development tax credit	$ 4,800,000
Research and development tax credits, expiration year	2030

Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Jan. 31, 2016	Oct. 31, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Caribou [Member]
Operating Leased Assets [Line Items]
Percentage of shares owned			5.50%
Caribou [Member] \| Maximum [Member] \| Development And Regulatory Milestones [Member]
Operating Leased Assets [Line Items]
Milestone payments			$ 6,400,000
Caribou [Member] \| Maximum [Member] \| Sales Based Milestones [Member]
Operating Leased Assets [Line Items]
Milestone payments			20,000,000
Property Leases [Member]
Operating Leased Assets [Line Items]
Rent expense			6,200,000	$ 6,000,000	$ 2,700,000
Property Leases [Member] \| Cambridge, Massachusetts [Member]
Operating Leased Assets [Line Items]
Operating lease security deposit	$ 2,200,000	$ 300,000
Capital lease obligation additional period of term of leases in years	3 years	5 years
Operating lease arrangement term	10 years
Number of lease years before optional extension and early termination can be exercised	6 years
Prepaid lease payments			$ 2,200,000

Commitments and Contingencies - Schedule of Future Minimum Lease Payments (Detail) - Property Leases [Member] $ in Thousands	Dec. 31, 2018 USD ($)
Operating Leased Assets [Line Items]
2019	$ 5,616
2020	4,963
2021	5,507
2022	3,861
Total future minimum lease payments	$ 19,947

Collaborations - Additional Information (Detail)	1 Months Ended			3 Months Ended								12 Months Ended				33 Months Ended	48 Months Ended
Collaborations - Additional Information (Detail)	Jul. 31, 2018 USD ($) shares	Apr. 30, 2016 USD ($)	Jan. 31, 2015 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) PerformanceObligation	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue				$ 7,880,000	$ 7,408,000	$ 7,677,000	$ 7,469,000	$ 6,668,000	$ 7,317,000	$ 5,917,000	$ 6,215,000		$ 30,434,000	$ 26,117,000	$ 16,479,000
Deferred revenue				55,932,000				59,868,000					55,932,000	59,868,000		$ 55,932,000	$ 55,932,000
Novartis [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional payments received on each target													1,000,000
Estimated fair value of units			$ 11,600,000
Difference between cash proceeds received and estimated fair value of preferred units			2,600,000
Novartis [Member] \| Scenario, Forecast [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Period allowed for editing limited number of platform targets												5 years
Novartis [Member] \| Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development based milestone payments under agreement			30,300,000
Regulatory based milestone payments for first indication			50,000,000
Regulatory based milestone payments for second indication			50,000,000
Sales based milestone payments under agreement			100,000,000
Novartis [Member] \| Maximum [Member] \| Scenario, Forecast [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Internalization fee milestone payment												$ 20,000,000
Milestone payment for additional post-internalization targets												4,000,000
Novartis [Member] \| Novartis Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred Revenue Additions			10,000,000
Technology access fees			20,000,000	15,000,000									15,000,000			15,000,000	15,000,000
Quarterly research payments			$ 1,000,000
Research Payments				15,000,000									15,000,000			15,000,000	15,000,000
Research term			5 years
One time collaboration payment				10,000,000									$ 10,000,000			10,000,000	10,000,000
Termination period of agreement													90 days
Novartis [Member] \| Novartis Agreement [Member] \| Scenario, Forecast [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Internalization fee												$ 50,000,000
Novartis [Member] \| Novartis Agreement [Member] \| Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total research funding			$ 20,000,000
Novartis [Member] \| Unit Purchase Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from issuance of preferred stock			$ 9,000,000
Novartis [Member] \| Novartis Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred Revenue Additions													$ 10,000,000				53,400,000
Technology access fees				20,000,000									20,000,000			20,000,000	20,000,000
Quarterly research payments				20,000,000									20,000,000			20,000,000	20,000,000
Proceeds from issuance of preferred stock													$ 9,000,000
Number of performance obligations \| PerformanceObligation													2
Transaction price													$ 59,000,000
Transaction price allocated to preferred units purchased at fair value													11,600,000
Collaboration revenue													10,300,000	9,300,000	7,800,000		38,900,000
Aggregate transaction price remaining to be recognized				18,500,000									$ 18,500,000			18,500,000	18,500,000
Aggregate transaction price remaining to be recognized, period													through December 2019
Accounts receivable				6,000,000				6,000,000					$ 6,000,000	6,000,000		6,000,000	6,000,000
Deferred revenue				14,500,000				11,200,000					14,500,000	11,200,000		14,500,000	14,500,000
Novartis [Member] \| Novartis Arrangement [Member] \| HSC and CAR-T Cell Products [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Remaining transaction price allocated to combined performance obligation of licenses and associated research activities													$ 47,400,000
Combined performance obligation of licenses and associated research activities, revenue recognition period													5 years
Regeneron Pharmaceuticals Inc. [Member] \| Regeneron Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred Revenue Additions		$ 75,000,000											$ 75,000,000
One time collaboration payment		$ 25,000,000
Termination period of agreement		180 days
Number of performance obligations \| PerformanceObligation													3
Transaction price													$ 125,000,000
Purchase of common stock through private placement													50,000,000
Collaboration term extension period		2 years
Royalty payment obligation expiration period		12 years
Transaction price allocated to common stock													50,000,000
Remaining transaction price allocated to combined performance obligation													75,000,000
Amount allocated to licenses to targets and associated research activities and evaluation plans													63,800,000
Amount allocated to technology collaboration and associated research activities													$ 11,200,000
Licenses to targets and associated research activities and evaluation plans performance period													6 years
Regeneron Pharmaceuticals Inc. [Member] \| Regeneron Agreement [Member] \| Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development based milestone payments under agreement		$ 25,000,000
Sales based milestone payments under agreement		185,000,000
Regulatory based milestone payments under agreement		110,000,000
Regeneron Pharmaceuticals Inc. [Member] \| Stock Purchase Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Purchase of common stock through private placement		$ 50,000,000
Regeneron Pharmaceuticals Inc. [Member] \| Co-Development and Co-Promotion Agreement Member [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Termination period of agreement	180 days
Compensation for prior work	$ 1,500,000
Payment of royalty percentage on net product sales	50.00%
Regeneron Pharmaceuticals Inc. [Member] \| Co-Development and Co-Promotion Agreement Member [Member] \| Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Options exercisable, number of shares exercisable \| shares	5
Collaborative arrangement obligation to be fund in development costs	$ 5,000,000
Regeneron Pharmaceuticals Inc. [Member] \| Regeneron Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred Revenue Additions																75,000,000
Collaboration revenue													$ 20,100,000	16,800,000	8,700,000	45,600,000
Aggregate transaction price remaining to be recognized				41,400,000									$ 41,400,000			41,400,000	41,400,000
Aggregate transaction price remaining to be recognized, period													through April 2022
Deferred revenue				41,400,000				54,100,000					$ 41,400,000	54,100,000		41,400,000	41,400,000
Due from related party				7,500,000				4,100,000					7,500,000	4,100,000	$ 500,000	7,500,000	7,500,000
Accounts receivable				$ 1,500,000				$ 4,500,000					$ 1,500,000	$ 4,500,000		1,500,000	$ 1,500,000
Regeneron Pharmaceuticals Inc. [Member] \| Regeneron Arrangement \| Research and Development Services [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue																$ 12,100,000

Equity-Based Compensation - Schedule of Equity-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	$ 17,046	$ 15,322	$ 6,715
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	8,994	7,280	4,083
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	$ 8,052	$ 8,042	$ 2,632

Equity-Based Compensation - Summary of Restricted Stock Activity (Detail)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Unvested, Beginning balance \| shares	479,822
Number of Shares, Granted \| shares	86,250
Number of Shares, Vested \| shares	(411,372)
Number of Shares, Cancelled \| shares	(45,627)
Number of Shares, Unvested, Ending balance \| shares	109,073
Weighted Average Grant Date Fair Value per Share, Unvested, Beginning balance \| $ / shares	$ 0.90
Weighted Average Grant Date Fair Value per Share, Granted \| $ / shares	22.98
Weighted Average Grant Date Fair Value per Share, Vested \| $ / shares	0.83
Weighted Average Grant Date Fair Value per Share, Cancelled \| $ / shares	8.31
Weighted Average Grant Date Fair Value per Share, Unvested, Ending balance \| $ / shares	$ 15.53

Equity-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized equity-based compensation expense related to restricted stock	$ 1.4
Weighted average grant date fair value per share	$ 15.05	$ 12.43	$ 6.48
Unrecognized compensation cost related to stock options	$ 38.2
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of unrecognized compensation costs	1 year 7 months 6 days
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of unrecognized compensation costs	2 years 10 months 24 days

Equity-Based Compensation - Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	2.70%	2.00%	1.30%
Expected life of options	6 years	6 years	6 years
Expected volatility of underlying stock	87.10%	93.90%	88.00%
Expected dividend yield	0.00%	0.00%	0.00%

Equity-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding, Beginning Balance \| shares	4,705,448
Number of options, Granted \| shares	2,128,126
Number of options, Exercised \| shares	(1,142,944)
Number of options, Forfeited \| shares	(652,967)
Number of Options, Outstanding, Ending Balance \| shares	5,037,663
Number of Options, Exercisable \| shares	1,736,487
Weighted Average Exercise Price per Share, Outstanding, Beginning Balance \| $ / shares	$ 12.09
Weighted Average Exercise Price per Share, Granted \| $ / shares	20.38
Weighted Average Exercise Price per Share, Exercised \| $ / shares	9.32
Weighted Average Exercise Price per Share, Forfeited \| $ / shares	16.59
Weighted Average Exercise Price per Share, Outstanding, Ending Balance \| $ / shares	15.63
Weighted Average Exercise Price per Share, Exercisable \| $ / shares	$ 11.42
Weighted Average Remaining Contractual Term, Outstanding	8 years 4 months 17 days
Weighted Average Remaining Contractual Term, Exercisable	7 years 4 months 2 days
Aggregate Intrinsic Value, Outstanding \| $	$ 8,940
Aggregate Intrinsic Value, Exercisable \| $	$ 6,360

Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net loss	$ (19,066)	$ (22,702)	$ (22,219)	$ (21,356)	$ (23,963)	$ (15,356)	$ (15,593)	$ (12,631)	$ (85,343)	$ (67,543)	$ (31,634)
Weighted average shares outstanding, basic and diluted	44,215	43,161	42,836	42,043	39,155	35,189	34,916	34,723	43,069	36,006	22,222
Net loss per share, basic and diluted	$ (0.43)	$ (0.53)	$ (0.52)	$ (0.51)	$ (0.61)	$ (0.44)	$ (0.45)	$ (0.36)	$ (1.98)	$ (1.88)	$ (1.42)

- Definition

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

+ References + Details

Loss Per Share - Potential Dilutive Securities Excluded from Computation of Diluted Net Loss Per Common Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	5,147	5,185	4,402
Unvested Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	109	480	1,362
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	5,038	4,705	3,040

Stockholders' Equity - Additional Information (Detail)							12 Months Ended
Stockholders' Equity - Additional Information (Detail)	Nov. 15, 2018 USD ($) shares	Oct. 12, 2018 USD ($)	Nov. 06, 2017 USD ($)	Nov. 01, 2017 $ / shares shares	May 11, 2016 USD ($) $ / shares shares	Apr. 25, 2016	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)
Class Of Stock [Line Items]
Number of common stock issued upon conversion of value							$ 28,548,000	$ 141,000,000	$ 167,139,000
Common stock par value per share \| $ / shares							$ 0.0001	$ 0.0001
Proceeds from common stock offering							$ 28,971,000	$ 141,000,000	$ 170,507,000
Accretion amount recognized							$ 0
Sales Agreement [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares \| shares	1,659,300
Proceeds from common stock offering	$ 29,000,000
Percentage of gross proceeds from common stock as sales agent cash commission		3.00%
Sales Agreement [Member] \| General and Administrative [Member]
Class Of Stock [Line Items]
Legal accounting and other fees	$ 400,000
Sales Agreement [Member] \| Maximum [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering		$ 100,000,000
IPO [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares \| shares					6,900,000
Common stock price per share \| $ / shares					$ 18.00
Proceeds from issuance initial public offering					$ 115,500,000
Reverse stock split ratio of common stock						0.588
Reverse stock split description							one-for-1.7 reverse stock split
Effective date of reverse stock split							Apr. 25, 2016
Convertible preferred stock conversion ratio							one-for-0.6465903
Conversion of convertible preferred stock into common stock \| shares					23,481,956
Private Placement [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares \| shares					3,055,554
Number of common stock issued upon conversion of value					$ 55,000,000
Public Offering [Member] \| Underwriting Agreement [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares \| shares				6,250,000
Common stock par value per share \| $ / shares				$ 0.0001
Proceeds from common stock offering			$ 141,000,000

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended								12 Months Ended
	May 31, 2016	Jul. 31, 2014	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
General and administrative expenses			$ 8,708	$ 8,270	$ 7,805	$ 7,406	$ 10,213	$ 5,711	$ 6,369	$ 5,732	$ 32,189	$ 28,025	$ 16,798
Research and development expense related to license and service agreements with related party			19,918	23,237	23,467	22,493	21,170	17,481	15,565	13,431	89,115	67,647	31,840
Collaboration revenue			7,880	$ 7,408	$ 7,677	$ 7,469	6,668	$ 7,317	$ 5,917	$ 6,215	30,434	26,117	$ 16,479
Deferred revenue			$ 55,932				59,868				$ 55,932	$ 59,868
Caribou [Member]
Related Party Transaction [Line Items]
Percentage of related party obligation		30.00%									30.00%	30.00%	30.00%
Percentage of shares owned			5.50%								5.50%
General and administrative expenses											$ 900	$ 500	$ 900
Research and development expense related to license and service agreements with related party													1,300
Novartis [Member] \| Collaborative Arrangement
Related Party Transaction [Line Items]
Percentage of shares owned			9.60%								9.60%
Common stock, shares acquired	277,777
Collaboration revenue											$ 10,300	9,300	$ 7,800
Accounts receivable			$ 6,000				6,000				6,000	6,000
Deferred revenue			$ 14,500				$ 11,200				$ 14,500	$ 11,200

401(k) Plan - Additional Information (Detail) - 401(k) plan [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution of employee contribution, percent	50.00%
Employer matching contribution, percent	6.00%
Employer discretionary contribution amount	$ 0.6

Unaudited Quarterly Results - Schedule of Results of Operations on Quarterly Basis (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Data [Abstract]
Collaboration revenue	$ 7,880	$ 7,408	$ 7,677	$ 7,469	$ 6,668	$ 7,317	$ 5,917	$ 6,215	$ 30,434	$ 26,117	$ 16,479
Operating expenses:
Research and development	19,918	23,237	23,467	22,493	21,170	17,481	15,565	13,431	89,115	67,647	31,840
General and administrative	8,708	8,270	7,805	7,406	10,213	5,711	6,369	5,732	32,189	28,025	16,798
Total operating expenses	28,626	31,507	31,272	29,899	31,383	23,192	21,934	19,163	121,304	95,672	48,638
Operating loss	(20,746)	(24,099)	(23,595)	(22,430)	(24,715)	(15,875)	(16,017)	(12,948)	(90,870)	(69,555)	(32,159)
Interest income	1,680	1,397	1,376	1,074	752	519	424	317	5,527	2,012	525
Net loss	$ (19,066)	$ (22,702)	$ (22,219)	$ (21,356)	$ (23,963)	$ (15,356)	$ (15,593)	$ (12,631)	$ (85,343)	$ (67,543)	$ (31,634)
Net loss per share, basic and diluted	$ (0.43)	$ (0.53)	$ (0.52)	$ (0.51)	$ (0.61)	$ (0.44)	$ (0.45)	$ (0.36)	$ (1.98)	$ (1.88)	$ (1.42)
Weighted average shares outstanding, basic and diluted	44,215	43,161	42,836	42,043	39,155	35,189	34,916	34,723	43,069	36,006	22,222