Intellia Therapeutics (NTLA) 10-K 26 Feb 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 19, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
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	Yes
Entity Current Reporting Status	No
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Interactive Data Current	Yes
Entity File Number	001-37766
Entity Tax Identification Number	36-4785571
Entity Address, Address Line One	40 Erie Street
Entity Address, Address Line Two	Suite 130
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	857
Local Phone Number	285-6200
Entity Incorporation, State or Country Code	DE
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Document Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		67,726,345
Entity Public Float			$ 1,182,698,098
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Part III of this Annual Report on Form 10-K incorporates by reference certain information from the registrant’s definitive Proxy Statement for its 2021 annual meeting of shareholders, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year end of December 31, 2020. Except with respect to information specifically incorporated by reference in this Form 10-K, the Proxy Statement is not deemed to be filed as part of this Form 10-K.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents	$ 160,020	$ 57,226
Marketable securities	437,351	222,500
Accounts receivable	2,130	4,620
Prepaid expenses and other current assets	17,016	5,135
Total current assets	616,517	289,481
Marketable securities - noncurrent		4,746
Property and equipment, net	15,943	17,996
Operating lease right-of-use assets	39,114	19,137
Other assets	4,748	2,920
Total Assets	676,322	334,280
Current Liabilities:
Accounts payable	10,460	3,941
Accrued expenses	25,554	13,273
Current portion of operating lease liability	5,696	5,745
Current portion of deferred revenue	22,544	12,674
Total current liabilities	64,254	35,633
Deferred revenue, net of current portion	51,387	16,136
Long-term operating lease liability	33,609	12,630
Commitments and contingencies (Note 8)
Stockholders’ Equity:
Common stock, $0.0001 par value; 120,000,000 shares authorized; 66,234,056 and 50,198,044 shares issued and outstanding at December 31, 2020 and 2019, respectively	7	5
Additional paid-in capital	962,173	570,493
Accumulated other comprehensive income	1	261
Accumulated deficit	(435,109)	(300,878)
Total stockholders’ equity	527,072	269,881
Total Liabilities and Stockholders’ Equity	$ 676,322	$ 334,280

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
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	66,234,056	66,234,056
Common stock, shares outstanding	50,198,044	50,198,044

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Collaboration revenue	$ 57,994	$ 43,103	$ 30,434
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses:
Research and development	$ 150,408	$ 108,413	$ 89,115
General and administrative	44,169	41,058	32,189
Total operating expenses	194,577	149,471	121,304
Operating loss	(136,583)	(106,368)	(90,870)
Interest income	2,352	6,835	5,527
Net loss	$ (134,231)	$ (99,533)	$ (85,343)
Net loss per share, basic and diluted	$ (2.40)	$ (2.11)	$ (1.98)
Weighted average shares outstanding, basic and diluted	55,987	47,247	43,069
Other comprehensive (loss) income:
Unrealized (loss) gain on marketable securities	$ (260)	$ 289	$ (28)
Comprehensive loss	$ (134,491)	$ (99,244)	$ (85,371)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Parenthetical) - Follow-on Offering [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
At The Market Offerings
Stock issuance cost	$ 151	$ 363	$ 424
Follow On Public Offering
Stock issuance cost	$ 669

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Follow On Public Offering	At The Market Offerings	Regeneron [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Follow-on Offering [Member]	Follow-on Offering [Member]Follow On Public Offering	Follow-on Offering [Member]At The Market Offerings	Follow-on Offering [Member]Regeneron [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member]Follow On Public Offering	Additional Paid-In Capital [Member]At The Market Offerings	Additional Paid-In Capital [Member]Regeneron [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member]Cumulative Effect, Period of Adoption, Adjustment [Member]
Beginning balance at Dec. 31, 2017	$ 300,597					$ 4				$ 421,706					$ (121,113)
Beginning balance (ASU 2014-09 [Member]) at Dec. 31, 2017					$ 5,431											$ 5,431
Beginning balance, shares at Dec. 31, 2017						42,384,623
Issuance of common stock			$ 28,548					$ 1				$ 28,547
Issuance of common stock, shares								1,659,300
Exercise of stock options	10,651									10,651
Exercise of stock options, shares						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 income (loss)	(28)													$ (28)
Net loss	(85,343)														(85,343)
Ending balance at Dec. 31, 2018	277,920					$ 5				478,968				(28)	(201,025)
Ending balance (ASC 842 [Member]) at Dec. 31, 2018					$ (320)											$ (320)
Ending balance, shares at Dec. 31, 2018						45,224,480
Issuance of common stock			72,256									72,256
Issuance of common stock, shares								4,518,579
Exercise of stock options	3,086									3,086
Exercise of stock options, shares						364,404
Issuance of shares under employee stock purchase plan	1,092									1,092
Issuance of shares under employee stock purchase plan, shares						90,581
Equity-based compensation	15,091									15,091
Other comprehensive income (loss)	289													289
Net loss	(99,533)														(99,533)
Ending balance at Dec. 31, 2019	$ 269,881					$ 5				570,493				261	(300,878)
Ending balance, shares at Dec. 31, 2019	50,198,044					50,198,044
Issuance of common stock		$ 296,607	$ 49,461	$ 12,580			$ 2				$ 296,605	$ 49,461	$ 12,580
Issuance of common stock, shares							11,815,069	2,270,161	925,218
Exercise of stock options	$ 11,574									11,574
Exercise of stock options, shares	840,824					840,824
Vesting of restricted stock units, shares						82,829
Issuance of shares under employee stock purchase plan	$ 1,557									1,557
Issuance of shares under employee stock purchase plan, shares						101,911
Equity-based compensation	19,903									19,903
Other comprehensive income (loss)	(260)													(260)
Net loss	(134,231)														(134,231)
Ending balance at Dec. 31, 2020	$ 527,072					$ 7				$ 962,173				$ 1	$ (435,109)
Ending balance, shares at Dec. 31, 2020	50,198,044					66,234,056

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended			80 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (134,231)	$ (99,533)	$ (85,343)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	6,311	5,587	4,464
Loss on disposal of property and equipment	35	1	75
Equity-based compensation	19,903	15,091	17,046
Accretion of investment premiums (discounts)	538	(3,725)	(676)
Changes in operating assets and liabilities:
Accounts receivable	2,490	2,927	2,924
Prepaid expenses and other current assets	(9,206)	(1,763)	310
Operating right-of-use assets	6,457	5,728
Other assets	83	153	1,022
Accounts payable	5,060	1,880	232
Accrued expenses	13,031	2,310	2,780
Deferred revenue	45,121	(27,122)	(3,936)
Operating lease liabilities	(5,504)	(4,774)
Other long-term liabilities			(155)
Net cash used in operating activities	(49,912)	(103,240)	(61,257)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(3,585)	(6,794)	(6,358)
Proceeds from sale of property and equipment			131
Purchases of marketable securities	(473,702)	(297,030)	(254,555)
Maturities of marketable securities	262,800	329,000
Net cash (used in) provided by investing activities	(214,487)	25,176	(260,782)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock				$ 1,117,600
Proceeds from options exercised	11,574	3,086	10,652
Issuance of shares through employee stock purchase plan	1,557	1,092	1,018
Net cash provided by financing activities	371,779	76,434	40,217
Net increase (decrease) in cash, cash equivalents and restricted cash equivalents	107,380	(1,630)	(281,822)
Cash, cash equivalents and restricted cash equivalents, beginning of period	57,226	58,856	340,678
Cash, cash equivalents and restricted cash equivalents, end of period	164,606	57,226	58,856	164,606
Reconciliation of cash, cash equivalents and restricted cash equivalents to consolidated balance sheet:
Cash and cash equivalents	160,020	57,226	58,856	160,020
Restricted cash equivalents, included in prepaids and other current assets and other assets	4,586			4,586
Cash, cash equivalents and restricted cash equivalents, end of period	164,606	57,226	58,856	164,606
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Purchases of property and equipment unpaid at period end	1,508	800	1,071
Right-of-use assets acquired under operating leases	26,432	2,554
Regeneron [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	12,580
Follow On Public Offering
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	296,607			438,300
At The Market Offerings
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	$ 49,461	$ 72,256	$ 28,547	$ 151,200

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) (Unaudited) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Follow On Public Offering
Net of issuance costs	$ 0.7	$ 0.7	$ 0.7
At The Market Offerings
Net of issuance costs	$ 0.2	$ 0.2	$ 0.2

The Company

The Company	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
The Company	1. Intellia Therapeutics, Inc. (“Intellia” or the “Company”) is a leading clinical-stage genome editing company, focused on developing proprietary, potentially curative CRISPR/Cas9-based therapeutics. CRISPR/Cas9, an acronym for C lustered, R egularly I nterspaced S hort P alindromic R epeats (“CRISPR”)/CRISPR associated 9 (“Cas9”), is a technology for genome editing, the process of altering selected sequences of genomic deoxyribonucleic acid (“DNA”). transform medicine by both producing therapeutics that permanently edit and/or correct disease-associated genes in the human body with a single treatment course, and creating enhanced engineered cells therapies. The Company’s combination of deep scientific, technical and clinical development experience, and proprietary innovations in genome editing and delivery technologies, along with its intellectual property (“IP”) portfolio, puts it in a position to unlock broad therapeutic applications of the CRISPR/Cas9 technology and create new classes of therapeutic products. 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 in development or 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. Liquidity Since its inception through December 31, 2020, the Company has raised an aggregate of $1,117.6 million to fund its operations, of which $272.6 million was through its collaboration agreements, $170.5 million was from its initial public offering (“IPO”) and concurrent private placements, $438.3 million was from follow-on public offerings, $151.2

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. 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. Comprehensive loss is comprised of net loss and gain/loss on marketable securities. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates, judgments and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates in these consolidated financial statements have been made in connection with the calculation of revenues, research and development expenses and equity-based compensation expense. The Company bases its estimates on historical experience and various other assumptions that management believes to be reasonable under the circumstances at the time such estimates are made. Actual results could differ from those estimates. The Company periodically reviews its estimates in light of changes in circumstances, facts and experience. The extent of the impact of the coronavirus disease 19 (“COVID-19”) pandemic on the Company’s operational and financial performance will depend on certain developments, including the length and severity of this pandemic, as well as its effect on our employees, collaborators and vendors, all of which are uncertain and cannot be predicted. The Company cannot reasonably estimate the extent to which the disruption may materially impact its consolidated results of operations or financial position. The effects of material revisions in estimates are reflected in the consolidated financial statements prospectively from the date of the change in estimate. Fair Value Measurements The Company’s financial instruments include cash equivalents, marketable securities, accounts receivable, accounts payable and accrued expenses. Certain of the Company’s financial assets, including 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 . Refer to Note 4 for further information regarding the Company’s fair value measurements. Other financial instruments, including accounts receivable, accounts payable and accrued expenses, 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, 2020 and 2019, cash equivalents consisted of interest-bearing money market accounts. Restricted Cash Equivalents The Company has restricted cash equivalents made up of money market funds held in collateral accounts that are restricted to secure a letter of credit in accordance with the lease for 281 Albany Street that the Company entered into in March of 2020 (see Note 10). The letter of credit, in the amount of $1.9 million, is required to be maintained throughout the term of the lease, which is ten years. These restricted cash equivalents are long-term in nature and are included in “Other Assets” in the Company’s consolidated balance sheet. The Company also has funds received from certain grants that are restricted as to their use and are therefore classified as restricted cash equivalents . These funds amounted to approximately $2.7 million as of December 31, 2020 and are included in “Prepaid Expenses and Other Current Assets” in the Company’s consolidated balance sheet as it is expected that they will be used within the next twelve months. Marketable Securities The Company’s marketable securities are accounted for as available-for-sale and recorded at fair value with the related unrealized gains and losses included in accumulated other comprehensive income (loss), a component of stockholders’ equity. Refer to Note 3 for further information regarding the Company’s marketable securities. 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, 2020, the Company’s collaboration partner, Regeneron, accounted for all of the Company’s accounts receivable. As of December 31, 2019, the Company’s two collaboration partners, 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% 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 Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) 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 9. In addition, none of the Company’s contracts as of December 31, 2020 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. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. As of December 31, 2020, 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, Collaborative Arrangements Licenses of intellectual property: 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. 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 probable. 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 or upon the achievement of milestones 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 . 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, allocated 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 stock-based compensation expense using the accelerated attribution method, based on its assessment of the probability that the performance condition will be achieved. The Company classifies equity-based compensation expense in its consolidated statement of operations and comprehensive loss 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 net (loss) income for each respective period by the weighted average number of common shares outstanding for each respective period. The Company computes diluted (loss) earnings per share after giving consideration to the dilutive effect of stock options and unvested restricted stock that are outstanding during the period, except where such 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 – Adopted In August 2018, the Financial Accounting Standards Board (“FASB”) ASU Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement . In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). The standard changes how credit losses are measured for most financial assets and certain other instruments. For trade and other receivables, the standard requires the use of a new forward-looking “expected credit loss” model that generally will result in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. With certain exceptions, the guidance is applied using a modified retrospective approach by reflecting adjustments through a cumulative-effect impact to retained earnings as of the beginning of the fiscal year of adoption. The Company adopted ASU 2016-13 on January 1, 2020. The adoption did not have a material effect on the Company’s consolidated financial statements as of and for the year ended December 3 1 , 2020 . Recent Accounting Pronouncements – Issued but not yet adopted In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes . .

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Marketable Securities	3. Marketable Securities The following table summarizes the Company’s available-for-sale marketable securities as of December 31, 2020 and 2019 at net book value: December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (In thousands) Marketable securities: U.S. Treasury and other government securities $ 245,666 $ 13 $ (11 ) $ 245,668 Financial institution debt securities 138,445 6 (8 ) 138,443 Corporate debt securities 41,765 3 (2 ) 41,766 Other asset-backed securities 11,474 1 (1 ) 11,474 Total $ 437,350 $ 23 $ (22 ) $ 437,351 December 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (In thousands) Marketable securities: U.S. Treasury securities $ 159,361 $ 142 $ (1 ) $ 159,502 Financial institution debt securities 40,173 105 - 40,278 Corporate debt securities 18,966 1 - 18,967 Other asset-backed securities 8,485 14 - 8,499 Total $ 226,985 $ 262 $ (1 ) $ 227,246 The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. At December 31, 2020 and 2019, the balance in the Company’s accumulated other comprehensive income was composed of activity related to the Company’s available-for-sale marketable securities. There were no material realized gains or losses in the years ended December 31, 2020, 2019 or 2018. The Company did not reclassify any amounts out of accumulated other comprehensive income The Company's available-for-sale securities that are classified as short - term marketable securities in the consolidated balance sheet mature within one year or less as of the balance sheet date. Available-for-sale securities that are classified as noncurrent in the consolidated balance sheet are those that mature after one year but within five years from the balance sheet date and that the Company does not inten d to dispose of within the next twelve months . At December 31, 20 20 and 201 9 , the Company did no t hold any investments that matured beyond five years of the balance sheet date .

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. 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, 2020 and 2019, the Company’s financial assets recognized at fair value on a recurring basis consisted of the following: Fair Value as of December 31, 2020 Total Level 1 Level 2 Level 3 (In thousands) Cash equivalents and restricted cash equivalents $ 163,805 $ 163,805 $ - $ - Marketable securities: U.S. Treasury and other government securities 245,668 241,664 4,004 - Financial institution debt securities 138,443 - 138,443 - Corporate debt securities 41,766 - 41,766 - Other asset-backed securities 11,474 - 11,474 - Total marketable securities 437,351 241,664 195,687 - Total $ 601,156 $ 405,469 $ 195,687 $ - Fair Value as of December 31, 2019 Total Level 1 Level 2 Level 3 (In thousands) Cash equivalents $ 46,917 $ 46,917 $ - $ - Marketable securities: U.S. Treasury securities 159,502 159,502 - - Financial institution debt securities 40,278 - 40,278 - Corporate debt securities 18,967 - 18,967 - Other asset-backed securities 8,499 - 8,499 - Total marketable securities 227,246 159,502 67,744 - Total $ 274,163 $ 206,419 $ 67,744 $ - Certain of the Company’s financial assets, including 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 its validation procedures, the Company did not adjust or override any fair value measurements provided by the pricing services as of December 31, 2020 or

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property and Equipment, Net	5 . Property and Equipment, Net Property and equipment, net consisted of the following: December 31, 2020 2019 (In thousands) Laboratory equipment $ 30,438 $ 27,199 Office furniture and equipment 1,181 1,121 Computer equipment 1,076 1,051 Leasehold improvements 1,520 1,474 Computer software 1,059 1,019 Total property and equipment 35,274 31,864 Less: accumulated depreciation and amortization (19,331 ) (13,868 ) Property and equipment, net $ 15,943 $ 17,996 Depreciation and amortization expense was $6.3 million, $5.6 million and $4.5 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued Expenses	6 . Accrued Expenses Accrued expenses consisted of the following: December 31, 2020 2019 (In thousands) Employee compensation and benefits $ 10,920 $ 6,311 Accrued research and development 11,008 4,208 Accrued legal and professional expenses 1,876 1,563 Accrued other 1,750 1,191 Total accrued expenses $ 25,554 $ 13,273

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	7 . 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, 2020 2019 2018 Federal statutory income tax rate (21.0 )% (21.0 )% (21.0 )% State income taxes (7.4 ) (8.9 ) (8.6 ) Research and development tax credits (1.8 ) (5.1 ) (4.7 ) Stock-based compensation (1.3 ) 1.2 (0.6 ) Change in valuation allowance 31.5 33.8 34.9 Effective income tax rate - % - % - % The Company’s net deferred tax assets (liabilities) consisted of the following: December 31, 2020 2019 (in thousands) Deferred tax assets: Intangibles, including acquired in-process research and development $ 981 $ 1,091 Capitalized start-up costs 378 421 Net operating loss carryforwards 101,807 63,245 Research and development credit carryforwards 23,166 19,417 Operating lease liability 10,713 5,008 Deferred revenue 4,680 7,843 Equity-based compensation 8,574 7,092 Accruals and allowances 2,200 1,245 Gross deferred tax assets 152,499 105,362 Deferred tax asset valuation allowance (140,868 ) (98,513 ) Total deferred tax assets 11,631 6,849 Deferred tax liabilities: Fixed assets (970 ) (1,633 ) Operating lease right-of-use assets (10,661 ) (5,216 ) Total deferred tax liabilities (11,631 ) (6,849 ) Net deferred tax asset (liability) $ - $ - As of December 31, 2020 and 2019, the Company had federal net operating loss carryforwards of $ 372.5 Approximately $37.2 million of the federal net operating losses generated prior to 2018 will begin to expire in 2034, unless previously utilized. Losses incurred prior to 2018 will generally be deductible to the extent of the lesser of a corporation’s net operating loss carryover or 100% of a corporation’s taxable income and be available for twenty years from the period the loss was generated. The federal net operating losses generated after 2017 of approximately $335.3 million will be carried over indefinitely, but will generally limit the net operating loss deduction to the lesser of the net operating loss carryforward or 80% of a corporation’s taxable income (subject to Section 382 of the Internal Revenue Code of 1986, as amended). Also there will be no carryback for losses incurred after 2017. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act, or the CARES Act, was enacted in the United States. The CARES Act temporarily removes the 80% limit for taxable years beginning before 2021 to allow an net operating loss carryforward to fully offset an organization’s income. The CARES Act allows a five-year As of December 31, 2020 and 2019, the Company also had state net operating loss carryforwards of $ 373.1 As of December 31, 2020 and 2019, the Company had federal tax credit carryforwards of approximately $15.0 million and $12.6 million, respectively, which begin to expire in 2034. As of December 31, 2020 and 2019, the Company had state research and development and other credit carryforwards of approximately $10.3 million and $ 8.7 in 2029 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, 20 20 and 201 9 . The valuation allowance increased by $ million in 20 20 , $ 34.5 million in 201 9 and $ million in 201 8 . 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, due to the significant cost and complexity associated with such a study. Any limitation may result in expiration of a portion of the net operating loss carryforward or research credit carryforward before utilization. A full valuation allowance has been provided against the Company’s net operating loss and tax credit carryforwards and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the balance sheet or statement of operations if an adjustment is required. As of December 31, 2020, 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 state taxing authorities for tax year 2017 through present. The returns in these jurisdictions since inception remain open for examination; however, there are currently no pending tax examinations. The Company will recognize interest and/or penalties related to uncertain tax benefits in income tax expense if they arise.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8 . Commitments and Contingencies Caribou Arbitration On October 17, 2018, the Company initiated an arbitration proceeding against Caribou Biosciences, Inc. (“Caribou”) asserting that Caribou violated the terms and conditions of a license agreement the Company entered into with them in July 2014 related to certain IP (the “Caribou License”), as well as other contractual and legal obligations to the Company, by using and seeking to license to third parties two patent families relating to specific structural or chemical modifications of guide RNAs (“gRNAs”), that were purportedly invented or controlled by Caribou, in the Company’s exclusive human therapeutic field, before an agreed-upon cutoff date of January 30, 2018. On September 26, 2019, the Company announced that the arbitration panel issued an interim award concluding that both the structural and chemical gRNA modification technologies were exclusively licensed to the Company by Caribou pursuant to the Caribou License. Nevertheless, the arbitration panel, solely with respect to the clinically modified gRNAs, stated that it will declare that Caribou has an equitable “leaseback”, which it described as exclusive, perpetual and worldwide (the “Caribou Award”). The Caribou Award does not include the structural guide modifications IP also at issue in the arbitration, any other IP exclusively licensed or sublicensed by Caribou to the Company under the Caribou License (including but not limited to the foundational CRISPR/Cas9 IP co-owned by the Regents of the University of California, University of Vienna and Dr. Emmanuelle Charpentier), or any other of the Company’s IP. On February 6, 2020, the panel clarified that the Caribou Award is limited to a particular on-going Caribou program, which seeks to develop a chimeric antigen receptor T (“CAR-T”) product directed at CD19. As instructed by the panel, the parties have been negotiating the terms of the Caribou Award, including Caribou’s future payments to the Company. If the negotiations are unsuccessful, the leaseback terms could be adjudicated in additional arbitration proceedings. Upon, and subject to the terms of, a final award, which will follow further arbitration or legal proceedings and potential additional negotiations between the parties, Caribou could be able to use the modified gRNAs at issue for CAR-T cell human therapeutics directed at CD19. Either the Company or Caribou may challenge the arbitration panel’s decisions under limited circumstances. Although the interim award has no effect on the Company’s rights or current programs nor on Caribou’s obligations under the Caribou License, the potential implications and impact the interim award may have cannot be predicted. License Agreement s The Company is party to license agreements, which include contingent payments. These payments will become payable if and when certain development, regulatory and commercial milestones are achieved. As of December 31, 2020, the satisfaction and timing of the contingent payments is uncertain and not reasonably estimable.

Collaborations

Collaborations	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaborations	9 . 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. As of December 31, 2020, the Company’s accounts receivable and contract liabilities were related to the Company’s collaboration with Regeneron. As of December 31, 2019, the Company’s accounts receivable and contract liabilities were related to the Company’s collaborations with Regeneron and Novartis. The following table presents changes in the Company’s accounts receivable and contract liabilities during the years ended December 31, 2020 and 2019 (in thousands): Balance at Beginning of Period Additions Deductions Balance at End of Period Year Ended December 31, 2020 Accounts receivable $ 4,620 $ 103,116 $ (105,606 ) $ 2,130 Contract liabilities: Deferred revenue $ 28,810 $ 87,477 $ (42,356 ) $ 73,931 Balance at Beginning of Period Additions Deductions Balance at End of Period Year Ended December 31, 2019 Accounts receivable $ 7,547 $ 15,999 $ (18,926 ) $ 4,620 Contract liabilities: Deferred revenue $ 55,932 $ 4,000 $ (31,122 ) $ 28,810 During the years ended December 31, 2020 and 2019, 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, 2020 Year Ended December 31, 2019 Amounts included in the contract liability at the beginning of the period $ 11,571 $ 27,122 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. Regeneron Pharmaceuticals, Inc. In April 2016, the Company entered into a license and collaboration agreement with Regeneron (the “2016 Regeneron Agreement”). The 2016 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-related 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. On May 30, 2020, the Company entered into (i) a mendment n o. 1 (the “ 2020 Regeneron Amendment”) to the 2016 Regeneron Agreement, (ii) c o- d evelopment and c o- f unding ag reements for the treatment of h emophilia A and h emophilia B (the “Hemophilia Co/Co ”) agreements and (iii) a s tock p urchase a greement (the “ 2020 Stock Purchase Agreement”). 2016 Regeneron Agreement: Scope. Under the initial six-year term of the 2016 Regeneron Agreement , Regeneron obtained exclusive rights for up to ten targets (the “Regeneron Target Cap”) to be chosen by Regeneron during the Technology Collaboration Term, as defined in the 2016 Regeneron Agreement, subject to a target selection process and various adjustments and limitations set forth in the 2016 Regeneron Agreement. Of these ten total targets, Regeneron may select up to five non-liver targets, while the remaining targets must be focused in the liver. The Company retains the exclusive right to solely develop certain in vivo products directed against specified genetic targets as well as certain non-liver targets from the Company’s ongoing and planned research activities. 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 collaboration term may be subject to co-development and co-promotion (“Co/Co”) agreements at the Company or Regeneron’s option. Regeneron has the option to enter into Co/Co agreements for up to five liver targets (other than the Company’s reserved liver targets) and the Company has the option to enter into one Intellia Independent Co/Co Option (as defined in the 2016 Regeneron Agreement). At the inception of the 2016 Regeneron Agreement, Regeneron selected the first of its ten targets, transthyretin amyloidosis (“ATTR”), which is subject to a Co/Co agreement between the Company and Regeneron (the “ATTR Co/Co”). The general terms and conditions for the ATTR Co/Co were outlined within the 2016 Regeneron Agreement. In addition, the Company granted Regeneron a non-exclusive, worldwide license, pursuant to which the Company and Regeneron will engage in research related activities aimed at discovering and developing novel technologies and improvements to CRISPR/Cas technology to enhance the Company’s genome editing platform. 2016 Regeneron Agreement: Financial Terms. In connection with the 2016 Regeneron Agreement, the Company received a nonrefundable upfront payment of $75.0 million. In addition, on Regeneron programs that are not subject to Co/Co 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. In connection with the 2016 Regeneron Agreement, Regeneron purchased $50.0 million of the Company’s common stock in a private placement under a stock purchase agreement concurrent with the Company’s IPO. 2020 Regeneron Amendment: Scope The 2020 Regeneron Amendment, among other things, (i) extends the Technology Collaboration Term until April 11, 2024, which Regeneron could extend for two additional years upon notice and a $30.0 million nonrefundable payment to the Company, (ii) increases the Regeneron Target Cap from ten to fifteen (with the additional five targets focused only in the liver) and (iii) allows for a second Intellia Independent Co/Co Option. The Company also granted a non-exclusive license to Regeneron under certain CRISPR/Cas platform IP for the commercialization of up to ten ex vivo edited CRISPR Products (as defined in the 2020 Regeneron Amendment) made using certain cell types, subject to certain limitations on Regeneron’s activities in T cells. The ex vivo license does not include access to the Company’s IP directed to its ex vivo targets, programs, or cell engineering processes. This non-exclusive license is subject to royalty obligations such that the Company is eligible to earn royalties on ex vivo edited CRISPR Products ranging from the high-single digits to low teens, in each case, on a per-product basis, subject to various reductions and offsets and the Company’s existing royalty obligations to Caribou. The Company transferred the license to develop the Factor VIII target for the treatment of hemophilia A to Regeneron. In addition, a target that was previously a Regeneron evaluation target was transferred back to the Company as an Intellia reserved liver target with certain reserved rights for Regeneron. In connection with the 2020 Regeneron Amendment, the Company and Regeneron also entered into the Hemophilia Co/Co agreements, which are directed to Factor VIII and Factor IX for the treatment of hemophilia A and hemophilia B. Factor VIII and Factor IX do not count toward the Regeneron Target Cap. Under the Hemophilia Co/Co agreements, which are substantially based upon the terms and conditions as outlined under the 2016 Regeneron Agreement, the Company and Regeneron will collaborate to research, develop, manufacture, and commercialize CRISPR Products for the treatment of hemophilia A and hemophilia B, for which Regeneron will be the Lead Party (as discussed below). Further, worldwide development costs and profits of any future products will be split between the Company and Regeneron, 35 % and 65 %, respectively, subject to certain deductions. 2020 Regeneron Amendment: Financial Terms. As part of the consideration for the 2020 Regeneron Amendment, Regeneron paid the Company an upfront payment of $70.0 million, which included the $25.0 million fee to extend the Technology Collaboration Term to April 2024. The potential future milestones and royalties remain unchanged from the 2016 Regeneron Agreement. In addition, on May 30, 2020, the Company and Regeneron entered into the 2020 Stock Purchase Agreement. Under the 2020 Stock Purchase Agreement, the Company sold to Regeneron 925,218 shares of its common stock, par value $0.0001 per share, for aggregate cash consideration of $30.0 million, or $32.42 per share (the “Equity Transaction”), representing a 100% premium over the volume-weighted average trading price of the Company’s common stock during the 30-day period prior to the closing of the Equity Transaction. Under the 2020 Stock Purchase Agreement, Regeneron will not dispose of any shares of common stock it beneficially owns in the Company until the termination of the Technology Collaboration Term. Research Collaboration. Research activities under the 2016 Regeneron Agreement and the 2020 Regeneron Amendment (collectively the “Amended Agreements”) 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 targets, and Regeneron will be responsible for preclinical research, conducting clinical development and manufacturing and commercialization of CRISPR Products directed to each of its exclusive selected 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 investigational new drug (“IND”), or other regulatory acceptance for at least one product directed to each applicable target and, following IND or other regulatory acceptance, to develop and commercialize at least one such product. Governance. Pursuant to the 2016 Regeneron Agreement, the parties formed a joint steering committee, which is responsible for setting research objectives and overseeing the general strategies and research and development activities undertaken by the parties. Term and Termination . Under the Amended Agreements, the Technology Collaboration Term ends in April 2024, except that Regeneron may make a one-time payment of $30.0 million to extend the Technology Collaboration Term for an additional two-year Co-Development and Co-Promotion Agreements. In July 2018, the Company and Regeneron finalized the form of the Co/Co agreement that will be used as the basis for each Co/Co agreement directed to a target. Simultaneously, the Company and Regeneron executed the ATTR Co/Co agreement, for which the Company is the clinical and commercial Lead Party and Regeneron is the Participating Party (each, as defined in the Co/Co agreements, as applicable, and described below). In May 2020, the Company and Regeneron executed the Hemophilia Co/Co agreements, for which Regeneron is the clinical and commercial Lead Party and the Company is the Participating Party . Co-Development and Co-Promotion: Agreement Structure. Under the 2016 Regeneron Agreement, Regeneron had the right to exercise at least four options, after ATTR, to enter into a Co/Co agreement for the Company’s liver targets (other than the Company’s reserved liver targets), while the Company had the opportunity to exercise at least one option to enter into a Co/Co agreement for Regeneron’s liver targets, the exact number of options being subject to certain conditions of the target selection process. In connection with the 2020 Regeneron Amendment, the Company received one additional option to enter into a Co/Co agreement, while Regeneron’s number of Co/Co options remained the same. Each option to enter into a Co/Co agreement must be exercised (or forfeited) once a target reaches a defined preclinical stage. One party will be the “Lead Party” and the other party the “Participating Party”. The Lead Party will have control and primary responsibility for the development, manufacturing, regulatory and commercial activities. The Participating Party will have the right to consult on these activities through its participation on the joint development and commercialization committees and will have the right to co-fund development and commercialization activities in exchange for a share of profits. In general, under each Co/Co agreement, 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%. Pursuant to the ATTR Co/Co, on December 13, 2019, Regeneron informed the Company that it would exercise its rights under the ATTR Co/Co agreement to modify its share of worldwide development costs and profits from 50% to 25%, which became effective in mid-June 2020. As noted above, in connection with the 2020 Regeneron Amendment, the Company and Regeneron entered into two Hemophilia Co/Co agreements. Under the Hemophilia Co/Co agreements, which are substantially based upon the Company and Regeneron’s previously agreed-upon form of Co/Co agreement, but do not count toward Regeneron’s total number of Co/Co options, the Company and Regeneron will collaborate to research, develop, manufacture, and commercialize CRISPR Products for the treatment of hemophilia A and hemophilia B. Regeneron will be the clinical and commercial lead for such activities. Co-Development and Co-Promotion: Governance. The parties formed j oint development and commercialization committees to oversee all profit share products under the Co/Co agreements as discussed below. The committees are responsible for overseeing the development, manufacture, regulatory matters, and commercialization (including pricing and reimbursement) efforts under the ATTR Co/Co and the Hemophilia Co/Co agreements. Co-Development and Co-Promotion: Termination. Either party may terminate a particular Co/Co agreement by providing 180 days written notice. If the Company terminates, the product subject to the Co/Co agreement becomes a Regeneron product, and is subject to all future milestone and royalty payment obligations under the 2016 Regeneron Agreement. If Regeneron terminates and has contributed at least $5.0 million in development costs under the particular Co/Co agreement, 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 and, if any, Regeneron IP incorporated into the relevant product. 2016 Regeneron Agreement: Accounting Analysis. The Company determined that the 2016 Regeneron Agreement is within the scope of ASU 2014-09, and its related amendments (collectively known as “ASC 606”). The Company evaluated the promised goods and services under the 2016 Regeneron Agreement and determined that it included three performance obligations: (i) a combined performance obligation including the licenses to targets and the associated research activities and evaluation plans; (ii) a combined performance obligation including the technology collaboration and associated research activities; and (iii) the common stock. Under the 2016 Regeneron Agreement, the Company determined that the transaction price was $125.0 million, consisting of the following consideration: (i) the nonrefundable upfront payment of $75.0 million; and (ii) the payment of 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 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 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 first allocated $50.0 million of the transaction price to the common stock. . using a time elapsed inputs method as this method provides the most faithful depiction of the entity’s performance in transferring control of the goods and services promised to Regeneron using a time elapsed inputs method as this method provides the most faithful depiction of the entity’s performance in transferring control of the goods and services promised to Regeneron . 2020 Regeneron Amendment: Accounting Analysis. The Company concluded that the accounting for the 2020 Regeneron Amendment is within the scope of ASC 606. The Company evaluated the promised goods and services under the 2020 Regeneron Amendment and determined that it included three performance obligations: (i) a combined performance obligation including the licenses to targets and the associated research activities and evaluation plans; (ii) a combined performance obligation including the technology collaboration and associated research activities; and (iii) the transfer of the license to develop the Factor VIII target for hemophilia A. The 2020 Regeneron Amendment represents a contract modification. The modification of the license to targets and the associated research activities and evaluation plans and the license to the technology collaboration and associated research activities are accounted for as if they were part of the original agreement and therefore form part of a performance obligation that was partially satisfied at the date of modification. The Company therefore recorded a cumulative catch-up adjustment of $8.4 million on the modification date. The Company accounted for the distinct performance obligation – specifically the obligation to transfer the license to develop the Factor VIII target for hemophilia A - as if it were a separate component of the modified contract. The transaction price of the 2020 Regeneron Amendment was determined to be $110.9 million, which is comprised of the $23.5 million remaining consideration from the 2016 Regeneron Agreement transferred at the inception of the arrangement, the $70.0 million upfront payment received upon the execution of the 2020 Regeneron Amendment and $17.4 million on the sale of shares under the 2020 Stock Purchase Agreement. The Company applied equity accounting guidance to measure the $12.6 million fair value recorded in the consolidated statement of stockholders’ equity upon issuance of the shares. All variable consideration will be fully constrained, until such point where the constraints can be lifted, at which point the Company will allocate the consideration to the performance obligations in the arrangement accordingly. The $110.9 million transaction price was allocated to the performance obligations including the licenses to targets and associated research activities and evaluation plans, the combined performance obligation including the technology collaboration and associated research activities and the transfer of the license to develop the Factor VIII target for hemophilia A, on a relative standalone selling price basis. The Company estimated the standalone selling price of the transfer of the license to develop the Factor VIII target for hemophilia A using the adjusted market assessment approach, whereby the Company estimated the market in which it sells goods or services and estimated the price that a customer in that market would be willing to pay for those goods or services. The Company estimated the standalone selling price of the combined performance obligation of the technology collaboration and associated research activities by taking into consideration internal estimates of research and development personnel needed to perform the research and development services. The estimated standalone selling price of the combined performance obligation, including the licenses to targets and the associated research activities and evaluation plans, was determined using selling prices of comparable transactions. As a result of this evaluation, the Company allocated $91.9 million to the combined performance obligation including the licenses to targets and associated research activities and evaluation plans, $3.7 million to the combined performance obligation including the technology collaboration and associated research activities, and $15.3 million to the transfer of the license to develop the Factor VIII target for hemophilia A. The $91.9 million allocated to the combined performance obligation, including the licenses to targets and associated research activities and evaluation plans, as well as the $3.7 million allocated to the combined performance obligation, including the technology collaboration and associated research activities, are being recognized using a time elapsed inputs method over the remaining period of the collaboration which, in management’s judgment, is the best measure of progress towards satisfying the performance obligation as this method provides the most faithful depiction of the entity’s performance in transferring control of the goods and services promised to Regeneron and represents the Company’s best estimate of the period of the obligation. The Company will re-evaluate the measure of progress in each reporting period and when events whose outcome are resolved or other changes in circumstances occur. The $15.3 million allocated to the transfer of the license to develop the Factor VIII target for hemophilia A was recognized when the Company transferred control of the hemophilia A target during the third quarter of 2020. Co/Co Agreements: Accounting Analysis. The Company concluded that the ATTR Co/Co and Hemophilia Co/Co agreements meet 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 cumulative amounts paid or received under the cost sharing provisions of the ATTR Co/Co and the Hemophilia Co/Co agreements as a component of revenues in the consolidated statements of operations and comprehensive loss, to the extent that this does not result in a cumulative “negative revenue” amount, in which case the cumulative shortfall would be reclassified as an expense. Revenue Recognition: Collaboration Revenue. Through December 31, 2020, excluding the amounts allocated to Regeneron’s purchase of the Company’s common stock, the Company recorded $145.0 million in upfront payments under the Amended Agreements and $34.8 million primarily for research and development services under the ATTR Co/Co agreement. Through December 31, 2020, the Company has recognized $123.2 million of collaboration revenue under all arrangements, including $53.0 million, $24.6 million and $20.1 million of collaboration revenue in the years ended December 31, 2020, 2019 and 2018, respectively, in the consolidated statements of operations and comprehensive loss . This includes $ million, $ 12.0 million, and $ 7.5 million primarily representing payments due from Regeneron pursuant to the ATTR Co/Co agreement . As of December 31, 2020, there was approximately $73.9 million of the aggregate transaction price of the Amended Agreements remaining to be recognized, which the Company expects to be recognized during the research term through April 2024. As of December 31, 2020 and 2019, the Company had accounts receivable of $2.1 million and $3.6 million, respectively, and deferred revenue of $73.9 million and $28.8 million, respectively, related to the Amended Agreements. Novartis Institutes for BioMedical Research, Inc. In December 2014, the Company entered into a strategic collaboration agreement with Novartis (the “2014 Novartis Agreement”), primarily focused on the research of new ex vivo Revenue Recognition – Collaboration Revenue. Through December 31, 2020, 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 $62.4 million in cash under the 2014 Novartis Agreement and the Novartis Amendment. Through December 31, 2020, the Company recognized $62.4 million of collaboration revenue. No revenue was recognized during the year ended December 31, 2020 related to the 2014 Novartis Agreement and the Novartis Amendment. The Company recognized $18.5 million and $10.3 million during the years ended December 31, 2019 and 2018, in the consolidated statements of operations and comprehensive loss, related to the 2014 Novartis Agreement and the Novartis Amendment. As of December 31, 2019, the aggregate transaction price had been recognized in full. Revenue Recognition – Milestone . During the year ended December 31, 2020, the U.S. Food and Drug Administration (“FDA”) accepted the IND application submitted by Novartis for a CRISPR/Cas9-based engineered cell therapy for the treatment of sickle cell disease. As a result of meeting this milestone, the Company recognized $5.0 million as collaboration revenue within the consolidated statement of operations and comprehensive loss. No other milestones under the 2014 Novartis Agreement and the Novartis Amendment were achieved during the years ended December 31, 2020, 2019 or 2018. The Company is eligible to receive additional downstream success-based milestones and royalties. As of December 31, 2020, the Company had no accounts receivable related to the 2014 Novartis Agreement and the Novartis Amendment. As of December 31, 2019, the Company had accounts receivable of $1.0 million related to the 2014 Novartis Agreement and the Novartis Amendment. As of December 31, 2020 and 2019, the Company had no deferred revenue related to the 2014 Novartis Agreement and the Novartis Amendment.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	1 0 . Leases In October 2014, the Company entered into an agreement to lease office and laboratory space at 130 Brookline Street (the “130 Brookline Lease”) 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 January 2025 In March 2020, the Company entered into a second amendment to the 130 Brookline Lease (the “130 Brookline Lease Second Amendment”). The 130 Brookline Lease Second Amendment amends certain terms of the Company’s existing lease, dated October 21, 2014, as amended on April 5, 2019. The 130 Brookline Lease Second Amendment extends the term of the 130 Brookline Lease by approximately six years through January 31, 2031. This extended term is included as part of the lease liability and right-of-use asset at December 31, 2020. The 130 Brookline Lease Second Amendment also provides an option to extend the lease for two consecutive five-year terms. The option for these further extensions is not included as part of the lease liability and right-of-use asset at December 31, 2020, as it is not reasonably certain that it will be exercised. In the first quarter of 2020, the Company increased the right-of-use asset and liability related to this lease by approximately $ 7.3 million related to the 130 Brookline Lease Second Amendment. In March 2019, the Company entered into a separate agreement to sublease additional office and laboratory space at 130 Brookline Street in Cambridge, Massachusetts under an operating sublease agreement with a term through April 2021, with two options to extend the agreement by one year each, for a total option period of up to two years. Upon commencement of the lease in April 2019, the Company recognized a right-of-use asset and lease liability of approximately $1.3 million. In September 2020, the Company amended the lease to extend the term until October 2021. An adjustment of $0.4 million to the right-of-use asset and lease liability was recorded upon the execution of the amendment. In January 2016, the Company entered into a ten-year 18.5 In March 2020, the Company entered into an agreement to lease approximately 39,000 square feet of office and laboratory space at 281 Albany Street in Cambridge, Massachusetts under an operating lease agreement (the “281 Albany Lease”). The Company’s obligation to pay rent will start on the date that is six months after the commencement date or the date on which the Company occupies the premises, whichever occurs earlier (the “Rent Commencement Date”). The initial term of the 281 Albany Lease is ten years following the Rent Commencement Date. As of December 31, 2020 the Company determined, in accordance with ASC 842, Leases Throughout the term of its leases, the Company is responsible for paying certain costs and expenses, in addition to the rent, as specified in the lease, including a proportionate share of applicable taxes, operating expenses and utilities. The variable portion of these costs are expensed as incurred and are disclosed as variable lease cost. The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the years ended December 31, 2020 and 2019: Year Ended December 31, 2020 2019 (In thousands) Lease cost Operating lease cost $ 8,447 $ 7,431 Short-term lease cost 56 53 Variable lease cost 2,918 2,218 Total lease cost $ 11,421 $ 9,702 Year Ended December 31, 2020 2019 (In thousands) Other information Operating cash flows used for operating leases $ 7,495 $ 6,476 Operating lease liabilities arising from obtaining right-of-use assets 26,432 2,554 As Of December 31, 2020 2019 Lease term and discount rate Weighted average remaining lease term 6.7 years 3.0 years Weighted average discount rate 5.80% 9.00% The table below reconciles the undiscounted cash flows for each of the next five years and total of the remaining years to the operating lease liabilities recorded in the consolidated balance sheet as of December 31, 2020: Future Operating Lease Payments Year Ending December 31, (in thousands) 2021 $ 7,803 2022 6,604 2023 6,744 2024 6,934 2025 7,322 Thereafter 13,631 Total lease payments $ 49,038 Less: imputed interest (9,733 ) Total operating lease liabilities at December 31, 2020 $ 39,305

Equity-Based Compensation

Equity-Based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity-Based Compensation	1 1 . Equity-Based Compensation In April 2016, the Company adopted the Amended and Restated 2015 Stock Option and Incentive Plan (the “2015 Plan”). The 2015 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock awards, restricted stock units (“RSUs”) and other stock-based awards. Recipients of incentive stock options and non-qualified stock options are eligible to purchase shares of the Company’s common stock at an exercise price equal to the fair value of such stock on the grant date. Stock options granted under the 2015 Plan generally vest 25% on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years, unless they contain specific performance-based vesting provisions. The maximum term of stock options granted under the 2015 Plan is ten years. As of December 31, 2020, there were 2,006,412 shares available for future issuance. The number of shares reserved for issuance under the 2015 Plan shall be cumulatively increased by four percent of the number of shares of stock issued and outstanding on the immediately preceding December 31 or such lesser number of shares of stock as determined by the board of directors . Equity-based compensation expense is classified in the consolidated statements of operations and comprehensive loss as follows: Year Ended December 31, 2020 2019 2018 (In thousands) Research and development $ 10,202 $ 6,986 $ 8,994 General and administrative 9,701 8,105 8,052 Total $ 19,903 $ 15,091 $ 17,046 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, 2020: Number of Shares Weighted Average Grant Date Fair Value per Share Unvested restricted stock as of December 31, 2019 71,875 $ 22.88 Granted 260,336 21.70 Vested (82,829 ) 17.31 Cancelled (55,446 ) 21.82 Unvested restricted stock as of December 31, 2020 193,936 $ 23.98 The weighted average grant date fair value of the 71,875 shares of restricted stock granted in 2018 and outstanding at December 31, 2019 was $22.88. These were all performance-based RSUs that would vest upon obtaining certain scientific and regulatory milestones through 20 . During the year ended December 31, 2020, 4 of these RSUs were cancelled as the performance criteria had not been met as of the milestone measurement date. There were no RSUs granted during the year ended December 31, 2019. During the year ended December 31, 2020, 2 of these RSUs vested as the performance criteria had been met as of the milestone measurement date. There was no unrecognized equity-based compensation expense related to these performance-based RSUs as of December 31, 2020. In January 2020, the Company granted 181,020 RSUs to certain non-executive employees that include a performance condition in addition to a service condition. These RSUs vest over a period of three years and are subject to accelerated vesting based on the Company’s programs achieving certain development milestones before December 1, 2022. The fair value of the RSUs at date of grant was $15.05. During the year ended December 31, 2020, the Company achieved one of its development milestones and 58,870 of these RSUs vested. This acceleration resulted in approximately $0.3 million in additional expense during the year ended December 31, 2020. In December 2020, the Company granted 79,316 36.89 As of December 31, 2020, there was $3.8 million of unrecognized equity-based compensation expense related to RSUs that are expected to vest. These costs are expected to be recognized over a weighted average remaining vesting period of 2.6 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 $9.07 per option for options granted during the year ended December 31, 2020, $9.21 per option for options granted during the year ended December 31, 201 9 and $ per option for options granted during the year ended December 31, 201 8 . The total intrinsic value (the amount by which the fair market value exceeded the exercise price) of stock options exercised during the year ended December 31, 20 20 , 201 9 and 201 8 was $ 20.3 million, $ 2.3 million, and $ million, respectively. The we ighted average assumptions used to apply this pricing model were as follows: Year Ended December 31, 2020 2019 2018 Risk-free interest rate 0.8 % 2.1 % 2.7 % Expected life of options 6.0 years 6.0 years 6.0 years Expected volatility of underlying stock 67.8 % 68.1 % 87.1 % Expected dividend yield 0.0 % 0.0 % 0.0 % Risk-free Interest Rate. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant with maturities approximately equal to the option’s expected term. Expected Dividend Yield. The expected dividend yield assumption is based on the fact that the Company has never paid cash dividends and has no present intention to pay cash dividends. Expected Volatility. The expected volatility was derived from a blend of average historical stock volatilities of several unrelated public companies within the Company’s industry and the Company’s historical volatility, both over a period equivalent to the expected term of the stock option grants. Expected Term. The expected term represents the period that stock option awards are expected to be outstanding. For option grants that are considered to be “plain vanilla,” the Company determines the expected term using the simplified method. The simplified method deems the term to be the average of the time-to-vesting and the contractual life of the options. The Company uses the simplified method because it does not have sufficient historical option exercise data to provide a reasonable basis upon which to estimate the expected term. The Company uses the market closing price of its common stock as reported on the Nasdaq Global Select Market to determine the fair value of the shares of common stock underlying stock options. The following is a summary of stock option activity for the year ended December 31, 2020: 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, 2019 5,365,971 $ 15.67 Granted 2,975,465 15.04 Exercised (840,824 ) 13.77 Forfeited (523,172 ) 18.41 Outstanding at December 31, 2020 6,977,440 $ 15.43 7.86 $ 271,940 Exercisable at December 31, 2020 2,950,493 $ 15.22 6.59 $ 115,608 As of December 31, 2020, there was $33.7 million of unrecognized compensation cost related to stock options that have not yet vested. These costs are expected to be recognized over a weighted average remaining vesting period of 2.5 years. Of the stock options outstanding as of December 31, 2020 and 2019, 77,916 and 213,750, respectively, were performance-based stock options that vest upon obtaining certain scientific, financial and regulatory milestones through 2020. During the year ended December 31, 2020, 47,916 of these performance-based options vested as the performance criteria had been met as of the milestone measurement date. During the year ended December 31, 2020 125,834 of these performance-based options were forfeited as the performance criteria had not been met as of the milestone measurement date. At December 31, 2019, 188,750 performance-based options

Loss Per Share

Loss Per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Loss Per Share	1 2 . Loss Per Share Basic and diluted loss per share was calculated as follows: Year Ended December 31, 2020 2019 2018 (In thousands) Net loss $ (134,231 ) $ (99,533 ) $ (85,343 ) Weighted average shares outstanding, basic and diluted 55,987 47,247 43,069 Net loss per share, basic and diluted $ (2.40 ) $ (2.11 ) $ (1.98 ) The following common stock equivalents were excluded from the calculation of diluted loss per share in 2020, 2019 and 2018 because their inclusion would have been anti-dilutive: Year Ended December 31, 2020 2019 2018 (In thousands) Unvested restricted stock 194 72 109 Stock options 6,977 5,366 5,038 7,171 5,438 5,147

Stockholders_ Equity

Stockholders’ Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Stockholders’ Equity	1 3 . Stockholders’ Equity Follow-on Offerings On June 1, 2020, the Company entered into an underwriting agreement related to a public offering of 6,301,370 shares of its common stock, par value $0.0001 per share, including the exercise in full by the underwriters of their option to purchase an additional 821,917 shares, at the public offering price of $18.25 per share. The offering closed on June 5, 2020 and the Company received net proceeds of $107.7 million, after deducting the underwriting discount, commissions and offering expenses. On December 1, 2020, the Company entered into an underwriting agreement related to a public offering of 5,513,699 shares of its common stock, par value $0.0001 per share, including the exercise in full by the underwriters of their option to purchase an additional 719,178 shares, at the public offering price of $36.50 per share. The offering closed on December 4, 2020 and the Company received net proceeds of $188.9 million, after deducting the underwriting discount, commissions and offering expenses. At-the-Market Offering Programs I n October 2018, the Company entered into an Open Market Sale Agreement (the “2018 Sales Agreement”) with Jefferies LLC (“Jefferies”), under which Jefferies was able to offer and sell, from time to time in “at-the-market” offerings, shares of its common stock having aggregate gross proceeds of up to $100.0 million. The Company paid to Jefferies cash commissions of 3.0% of the gross proceeds of sales of common stock under the 2018 Sales Agreement. he Company issued 5,890,648 shares of its common stock at an average price of $16.98 per share in accordance with the 2018 Sales Agreement for aggregate net proceeds of $96.4 million, after payment of cash commissions to Jefferies and approximately $0.6 million related to legal, accounting and other fees in connection with All shares related to the 2018 Sales Agreement had been sold as of December 31, 2019 I n August 2019, the Company entered into an Open Market Sale Agreement (the “2019 Sales Agreement”) with Jefferies, under which Jefferies was able to offer and sell, from time to time in “at-the-market” offerings, common stock having aggregate gross proceeds of up to $150.0 million. The Company agreed to pay Jefferies cash commissions of 3.0 % of the gross proceeds of sales of common stock under the 2019 Sales Agreement. During the year ended December 31, 2019, the Company issued 287,231 shares of its common stock, in a series of sales, at an average price of $ 16.48 per share, in accordance with the 2019 Sales Agreement for aggregate net proceeds of $ 4.4 million, after payment of cash commissions to Jefferies and approximately $ 0.2 million related to legal, accounting and other fees in connection with the sales. During the year ended Dec ember 3 1 , 2020, the Company issued shares of its common stock in a series of sales at an average price of $ per share in accordance with the 2019 Sales Agreement, for aggregate net proceeds of $ million after payment of cash commissions to Jefferies and approximately $ million related to legal, accounting and other fees in connection with the sales. As of December 31, 2020, $94.1 million in shares of common stock remain eligible for sale under the 2019 Sales Agreement. Shares Issued in Private Placement to Regeneron As described in Note 9 above, in May 2020 the Company entered into an amendment to its collaboration agreement with Regeneron that was entered into in April 2016. Simultaneously, the Company and Regeneron entered into the 2020 Stock Purchase Agreement , under which the Company sold to Regeneron 925,218 shares of its common stock, par value $0.0001 per share, for aggregate cash consideration of $30.0 million, or $32.42 per share, representing a 100% premium over the volume-weighted average trading price of the Company’s common stock during the 30-day period prior to the closing. Under the 2020 Stock Purchase Agreement, Regeneron will not dispose of any shares of common stock it beneficially owns in the Company until the termination of the Technology Collaboration Term (see Note 9). After applying equity accounting guidance to measure the issuance of the shares, $12.6 million was recorded as fair value in the consolidated statement of stockholders’ equity for the shares.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	1 4 . Related Party Transactions In the ordinary course of business, the Company may purchase materials or supplies from entities that are associated with a party that meets the criteria of a related party of the Company. These transactions are reviewed quarterly and to date have not been material to the Company’s consolidated financial statements.

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
401(k) Plan	1 5 . 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. The Company makes matching contributions of 50% of the first 6% of employee contributions. The Company made matching contributions of $ 1.1 million, $0.8 million and $0.6 million for the years ended December 31, 2020, 2019 and 2018, respectively

Unaudited Quarterly Results

Unaudited Quarterly Results	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Unaudited Quarterly Results	1 6 . Unaudited Quarterly Results The results of operations on a quarterly basis for the years ended December 31, 2020 and 2019 are set forth below: March 31, 2020 June 30, 2020 September 30, 2020 December 31, 2020 (Amounts in thousands except per share data) Collaboration revenue $ 12,916 $ 16,263 $ 22,220 $ 6,595 Operating expenses: Research and development 34,650 37,771 39,756 38,231 General and administrative 11,314 11,526 10,566 10,763 Total operating expenses 45,964 49,297 50,322 48,994 Operating loss (33,048 ) (33,034 ) (28,102 ) (42,399 ) Interest income 1,242 641 262 207 Net loss $ (31,806 ) $ (32,393 ) $ (27,840 ) $ (42,192 ) Net loss per share, basic and diluted $ (0.63 ) $ (0.61 ) $ (0.47 ) $ (0.69 ) Weighted average shares outstanding, basic and diluted 50,491 53,369 58,754 61,306 March 31, 2019 June 30, 2019 September 30, 2019 December 31, 2019 (Amounts in thousands except per share data) Collaboration revenue $ 10,433 $ 11,118 $ 10,616 $ 10,936 Operating expenses: Research and development 23,709 25,460 27,513 31,731 General and administrative 10,533 13,118 8,431 8,976 Total operating expenses 34,242 38,578 35,944 40,707 Operating loss (23,809 ) (27,460 ) (25,328 ) (29,771 ) Interest income 1,869 1,777 1,694 1,495 Net loss $ (21,940 ) $ (25,683 ) $ (23,634 ) $ (28,276 ) Net loss per share, basic and diluted $ (0.49 ) $ (0.56 ) $ (0.49 ) $ (0.57 ) Weighted average shares outstanding, basic and diluted 45,234 45,814 48,554 49,350

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	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. Comprehensive loss is comprised of net loss and gain/loss on marketable securities.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates, judgments and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates in these consolidated financial statements have been made in connection with the calculation of revenues, research and development expenses and equity-based compensation expense. The Company bases its estimates on historical experience and various other assumptions that management believes to be reasonable under the circumstances at the time such estimates are made. Actual results could differ from those estimates. The Company periodically reviews its estimates in light of changes in circumstances, facts and experience. The extent of the impact of the coronavirus disease 19 (“COVID-19”) pandemic on the Company’s operational and financial performance will depend on certain developments, including the length and severity of this pandemic, as well as its effect on our employees, collaborators and vendors, all of which are uncertain and cannot be predicted. The Company cannot reasonably estimate the extent to which the disruption may materially impact its consolidated results of operations or financial position. The effects of material revisions in estimates are reflected in the consolidated financial statements prospectively from the date of the change in estimate.
Fair Value Measurements	Fair Value Measurements The Company’s financial instruments include cash equivalents, marketable securities, accounts receivable, accounts payable and accrued expenses. Certain of the Company’s financial assets, including 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 . Refer to Note 4 for further information regarding the Company’s fair value measurements. Other financial instruments, including accounts receivable, accounts payable and accrued expenses, are carried at cost, which approximate fair value due to the short duration and term to maturity.
Cash Equivalents	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, 2020 and 2019, cash equivalents consisted of interest-bearing money market accounts.
Restricted Cash Equivalents	Restricted Cash Equivalents The Company has restricted cash equivalents made up of money market funds held in collateral accounts that are restricted to secure a letter of credit in accordance with the lease for 281 Albany Street that the Company entered into in March of 2020 (see Note 10). The letter of credit, in the amount of $1.9 million, is required to be maintained throughout the term of the lease, which is ten years. These restricted cash equivalents are long-term in nature and are included in “Other Assets” in the Company’s consolidated balance sheet. The Company also has funds received from certain grants that are restricted as to their use and are therefore classified as restricted cash equivalents . These funds amounted to approximately $2.7 million as of December 31, 2020 and are included in “Prepaid Expenses and Other Current Assets” in the Company’s consolidated balance sheet as it is expected that they will be used within the next twelve months.
Marketable Securities	Marketable Securities The Company’s marketable securities are accounted for as available-for-sale and recorded at fair value with the related unrealized gains and losses included in accumulated other comprehensive income (loss), a component of stockholders’ equity. Refer to Note 3 for further information regarding the Company’s marketable securities.
Concentrations of Credit Risk	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, 2020, the Company’s collaboration partner, Regeneron, accounted for all of the Company’s accounts receivable. As of December 31, 2019, the Company’s two collaboration partners, Regeneron and Novartis Institutes for BioMedical Research, Inc. (“Novartis”), accounted for all of the Company’s accounts receivable .
Property and Equipment	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	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	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% 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	Revenue Recognition The Company adopted Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) 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 9. In addition, none of the Company’s contracts as of December 31, 2020 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. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. As of December 31, 2020, 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, Collaborative Arrangements Licenses of intellectual property: 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. 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 probable. 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 or upon the achievement of milestones 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 .
Research and Development Expenses	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, allocated 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	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 stock-based compensation expense using the accelerated attribution method, based on its assessment of the probability that the performance condition will be achieved. The Company classifies equity-based compensation expense in its consolidated statement of operations and comprehensive loss 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	(Loss) Earnings per Share The Company calculates basic (loss) earnings per share by dividing net (loss) income for each respective period by the weighted average number of common shares outstanding for each respective period. The Company computes diluted (loss) earnings per share after giving consideration to the dilutive effect of stock options and unvested restricted stock that are outstanding during the period, except where such securities would be anti-dilutive.
Segment Information	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 – Adopted	Recent Accounting Pronouncements – Adopted In August 2018, the Financial Accounting Standards Board (“FASB”) ASU Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement . In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). The standard changes how credit losses are measured for most financial assets and certain other instruments. For trade and other receivables, the standard requires the use of a new forward-looking “expected credit loss” model that generally will result in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. With certain exceptions, the guidance is applied using a modified retrospective approach by reflecting adjustments through a cumulative-effect impact to retained earnings as of the beginning of the fiscal year of adoption. The Company adopted ASU 2016-13 on January 1, 2020. The adoption did not have a material effect on the Company’s consolidated financial statements as of and for the year ended December 3 1 , 2020 .
Recent Accounting Pronouncements – Issued but not yet adopted	Recent Accounting Pronouncements – Issued but not yet adopted In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes . .

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
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

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Summary of Available-for-sale Marketable Securities	The following table summarizes the Company’s available-for-sale marketable securities as of December 31, 2020 and 2019 at net book value: December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (In thousands) Marketable securities: U.S. Treasury and other government securities $ 245,666 $ 13 $ (11 ) $ 245,668 Financial institution debt securities 138,445 6 (8 ) 138,443 Corporate debt securities 41,765 3 (2 ) 41,766 Other asset-backed securities 11,474 1 (1 ) 11,474 Total $ 437,350 $ 23 $ (22 ) $ 437,351 December 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (In thousands) Marketable securities: U.S. Treasury securities $ 159,361 $ 142 $ (1 ) $ 159,502 Financial institution debt securities 40,173 105 - 40,278 Corporate debt securities 18,966 1 - 18,967 Other asset-backed securities 8,485 14 - 8,499 Total $ 226,985 $ 262 $ (1 ) $ 227,246

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Assets Recognized at Fair Value on Recurring Basis	As of December 31, 2020 and 2019, the Company’s financial assets recognized at fair value on a recurring basis consisted of the following: Fair Value as of December 31, 2020 Total Level 1 Level 2 Level 3 (In thousands) Cash equivalents and restricted cash equivalents $ 163,805 $ 163,805 $ - $ - Marketable securities: U.S. Treasury and other government securities 245,668 241,664 4,004 - Financial institution debt securities 138,443 - 138,443 - Corporate debt securities 41,766 - 41,766 - Other asset-backed securities 11,474 - 11,474 - Total marketable securities 437,351 241,664 195,687 - Total $ 601,156 $ 405,469 $ 195,687 $ - Fair Value as of December 31, 2019 Total Level 1 Level 2 Level 3 (In thousands) Cash equivalents $ 46,917 $ 46,917 $ - $ - Marketable securities: U.S. Treasury securities 159,502 159,502 - - Financial institution debt securities 40,278 - 40,278 - Corporate debt securities 18,967 - 18,967 - Other asset-backed securities 8,499 - 8,499 - Total marketable securities 227,246 159,502 67,744 - Total $ 274,163 $ 206,419 $ 67,744 $ -

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment, net consisted of the following: December 31, 2020 2019 (In thousands) Laboratory equipment $ 30,438 $ 27,199 Office furniture and equipment 1,181 1,121 Computer equipment 1,076 1,051 Leasehold improvements 1,520 1,474 Computer software 1,059 1,019 Total property and equipment 35,274 31,864 Less: accumulated depreciation and amortization (19,331 ) (13,868 ) Property and equipment, net $ 15,943 $ 17,996

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following: December 31, 2020 2019 (In thousands) Employee compensation and benefits $ 10,920 $ 6,311 Accrued research and development 11,008 4,208 Accrued legal and professional expenses 1,876 1,563 Accrued other 1,750 1,191 Total accrued expenses $ 25,554 $ 13,273

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 2018 Federal statutory income tax rate (21.0 )% (21.0 )% (21.0 )% State income taxes (7.4 ) (8.9 ) (8.6 ) Research and development tax credits (1.8 ) (5.1 ) (4.7 ) Stock-based compensation (1.3 ) 1.2 (0.6 ) Change in valuation allowance 31.5 33.8 34.9 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, 2020 2019 (in thousands) Deferred tax assets: Intangibles, including acquired in-process research and development $ 981 $ 1,091 Capitalized start-up costs 378 421 Net operating loss carryforwards 101,807 63,245 Research and development credit carryforwards 23,166 19,417 Operating lease liability 10,713 5,008 Deferred revenue 4,680 7,843 Equity-based compensation 8,574 7,092 Accruals and allowances 2,200 1,245 Gross deferred tax assets 152,499 105,362 Deferred tax asset valuation allowance (140,868 ) (98,513 ) Total deferred tax assets 11,631 6,849 Deferred tax liabilities: Fixed assets (970 ) (1,633 ) Operating lease right-of-use assets (10,661 ) (5,216 ) Total deferred tax liabilities (11,631 ) (6,849 ) Net deferred tax asset (liability) $ - $ -

Collaborations (Tables)

Collaborations (Tables)	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Changes in Accounts Receivable and Contract Liabilities	The following table presents changes in the Company’s accounts receivable and contract liabilities during the years ended December 31, 2020 and 2019 (in thousands): Balance at Beginning of Period Additions Deductions Balance at End of Period Year Ended December 31, 2020 Accounts receivable $ 4,620 $ 103,116 $ (105,606 ) $ 2,130 Contract liabilities: Deferred revenue $ 28,810 $ 87,477 $ (42,356 ) $ 73,931 Balance at Beginning of Period Additions Deductions Balance at End of Period Year Ended December 31, 2019 Accounts receivable $ 7,547 $ 15,999 $ (18,926 ) $ 4,620 Contract liabilities: Deferred revenue $ 55,932 $ 4,000 $ (31,122 ) $ 28,810
Summary of Revenues Recognized Resulting From Changes in Contract Liability Balance	During the years ended December 31, 2020 and 2019, 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, 2020 Year Ended December 31, 2019 Amounts included in the contract liability at the beginning of the period $ 11,571 $ 27,122

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Summary of Lease Costs and Other Information	The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the years ended December 31, 2020 and 2019: Year Ended December 31, 2020 2019 (In thousands) Lease cost Operating lease cost $ 8,447 $ 7,431 Short-term lease cost 56 53 Variable lease cost 2,918 2,218 Total lease cost $ 11,421 $ 9,702 Year Ended December 31, 2020 2019 (In thousands) Other information Operating cash flows used for operating leases $ 7,495 $ 6,476 Operating lease liabilities arising from obtaining right-of-use assets 26,432 2,554 As Of December 31, 2020 2019 Lease term and discount rate Weighted average remaining lease term 6.7 years 3.0 years Weighted average discount rate 5.80% 9.00%
Schedule of Reconciliation of Undiscounted Cash Flows for Operating Lease Liabilities / Future Minimum Lease Payments	The table below reconciles the undiscounted cash flows for each of the next five years and total of the remaining years to the operating lease liabilities recorded in the consolidated balance sheet as of December 31, 2020: Future Operating Lease Payments Year Ending December 31, (in thousands) 2021 $ 7,803 2022 6,604 2023 6,744 2024 6,934 2025 7,322 Thereafter 13,631 Total lease payments $ 49,038 Less: imputed interest (9,733 ) Total operating lease liabilities at December 31, 2020 $ 39,305

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
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 and comprehensive loss as follows: Year Ended December 31, 2020 2019 2018 (In thousands) Research and development $ 10,202 $ 6,986 $ 8,994 General and administrative 9,701 8,105 8,052 Total $ 19,903 $ 15,091 $ 17,046
Summary of Restricted Stock Activity	The following table summarizes the Company’s restricted stock activity for the year ended December 31, 2020: Number of Shares Weighted Average Grant Date Fair Value per Share Unvested restricted stock as of December 31, 2019 71,875 $ 22.88 Granted 260,336 21.70 Vested (82,829 ) 17.31 Cancelled (55,446 ) 21.82 Unvested restricted stock as of December 31, 2020 193,936 $ 23.98
Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted	The we ighted average assumptions used to apply this pricing model were as follows: Year Ended December 31, 2020 2019 2018 Risk-free interest rate 0.8 % 2.1 % 2.7 % Expected life of options 6.0 years 6.0 years 6.0 years Expected volatility of underlying stock 67.8 % 68.1 % 87.1 % 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, 2020: 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, 2019 5,365,971 $ 15.67 Granted 2,975,465 15.04 Exercised (840,824 ) 13.77 Forfeited (523,172 ) 18.41 Outstanding at December 31, 2020 6,977,440 $ 15.43 7.86 $ 271,940 Exercisable at December 31, 2020 2,950,493 $ 15.22 6.59 $ 115,608

Loss Per Share (Tables)

Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 2018 (In thousands) Net loss $ (134,231 ) $ (99,533 ) $ (85,343 ) Weighted average shares outstanding, basic and diluted 55,987 47,247 43,069 Net loss per share, basic and diluted $ (2.40 ) $ (2.11 ) $ (1.98 )
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 2020, 2019 and 2018 because their inclusion would have been anti-dilutive: Year Ended December 31, 2020 2019 2018 (In thousands) Unvested restricted stock 194 72 109 Stock options 6,977 5,366 5,038 7,171 5,438 5,147

Unaudited Quarterly Results (Ta

Unaudited Quarterly Results (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 and 2019 are set forth below: March 31, 2020 June 30, 2020 September 30, 2020 December 31, 2020 (Amounts in thousands except per share data) Collaboration revenue $ 12,916 $ 16,263 $ 22,220 $ 6,595 Operating expenses: Research and development 34,650 37,771 39,756 38,231 General and administrative 11,314 11,526 10,566 10,763 Total operating expenses 45,964 49,297 50,322 48,994 Operating loss (33,048 ) (33,034 ) (28,102 ) (42,399 ) Interest income 1,242 641 262 207 Net loss $ (31,806 ) $ (32,393 ) $ (27,840 ) $ (42,192 ) Net loss per share, basic and diluted $ (0.63 ) $ (0.61 ) $ (0.47 ) $ (0.69 ) Weighted average shares outstanding, basic and diluted 50,491 53,369 58,754 61,306 March 31, 2019 June 30, 2019 September 30, 2019 December 31, 2019 (Amounts in thousands except per share data) Collaboration revenue $ 10,433 $ 11,118 $ 10,616 $ 10,936 Operating expenses: Research and development 23,709 25,460 27,513 31,731 General and administrative 10,533 13,118 8,431 8,976 Total operating expenses 34,242 38,578 35,944 40,707 Operating loss (23,809 ) (27,460 ) (25,328 ) (29,771 ) Interest income 1,869 1,777 1,694 1,495 Net loss $ (21,940 ) $ (25,683 ) $ (23,634 ) $ (28,276 ) Net loss per share, basic and diluted $ (0.49 ) $ (0.56 ) $ (0.49 ) $ (0.57 ) Weighted average shares outstanding, basic and diluted 45,234 45,814 48,554 49,350

The Company - Additional Inform

The Company - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended			80 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering				$ 1,117,600
Proceeds from issuance of convertible preferred stock				85,000
Collaborative Arrangement [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering				272,600
Initial Public Offering and Concurrent Private Placements [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering				170,500
Follow-on public Offerings [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering	$ 296,607			438,300
At The Market Offerings
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering	$ 49,461	$ 72,256	$ 28,547	$ 151,200

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)Segment
Summary Of Significant Accounting Policies [Line Items]
Restricted cash equivalents	$ 4,586
Percentage of likelihood of realization required to record tax benefit	50.00%
Number of reportable segment | Segment	1
Albany Lease [Member]
Summary Of Significant Accounting Policies [Line Items]
Term of lease	10 years
Albany Lease [Member] | Other Assets [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash equivalents	$ 1,900
Albany Lease [Member] | Prepaid Expense and Other Current Assets [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash equivalents	$ 2,700

Summary of Significant Accoun_5

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, 2020
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

Marketable Securities - Summary

Marketable Securities - Summary of Available -for-sale Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Amortized Cost	$ 437,350	$ 226,985
Gross Unrealized Gains	23	262
Gross Unrealized Losses	(22)	(1)
Estimated Fair Value	437,351	227,246
U.S. Treasury and Other Government Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	245,666
Gross Unrealized Gains	13
Gross Unrealized Losses	(11)
Estimated Fair Value	245,668
Financial Institution Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	138,445	40,173
Gross Unrealized Gains	6	105
Gross Unrealized Losses	(8)
Estimated Fair Value	138,443	40,278
Corporate Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	41,765	18,966
Gross Unrealized Gains	3	1
Gross Unrealized Losses	(2)
Estimated Fair Value	41,766	18,967
Other Asset Backed Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	11,474	8,485
Gross Unrealized Gains	1	14
Gross Unrealized Losses	(1)
Estimated Fair Value	$ 11,474	8,499
U.S. Treasury Securities [Member]
Marketable Securities [Line Items]
Amortized Cost		159,361
Gross Unrealized Gains		142
Gross Unrealized Losses		(1)
Estimated Fair Value		$ 159,502

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Marketable Securities [Line Items]
Realized gains or losses on marketable securities	$ 0	$ 0	$ 0
Investments that matured beyond five years	$ 0	$ 0
Minimum [Member]
Marketable Securities [Line Items]
Available-for-sales Securities, non-current, maturity period	1 year
Maximum [Member]
Marketable Securities [Line Items]
Available-for-sales Securities, non-current, maturity period	5 years

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Recognized at Fair Value on Recurring Basis (Detail) - Fair Value on Recurring Basis [Member] - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents and restricted cash equivalents	$ 163,805	$ 46,917
Marketable securities:
Marketable securities	437,351	227,246
Total	601,156	274,163
U.S. Treasury and Other Government Securities [Member]
Marketable securities:
Marketable securities	245,668
Financial Institution Debt Securities [Member]
Marketable securities:
Marketable securities	138,443	40,278
Corporate Debt Securities [Member]
Marketable securities:
Marketable securities	41,766	18,967
Other Asset Backed Securities [Member]
Marketable securities:
Marketable securities	11,474	8,499
U.S. Treasury Securities [Member]
Marketable securities:
Marketable securities		159,502
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents and restricted cash equivalents	163,805	46,917
Marketable securities:
Marketable securities	241,664	159,502
Total	405,469	206,419
Level 1 [Member] | U.S. Treasury and Other Government Securities [Member]
Marketable securities:
Marketable securities	241,664
Level 1 [Member] | U.S. Treasury Securities [Member]
Marketable securities:
Marketable securities		159,502
Level 2 [Member]
Marketable securities:
Marketable securities	195,687	67,744
Total	195,687	67,744
Level 2 [Member] | U.S. Treasury and Other Government Securities [Member]
Marketable securities:
Marketable securities	4,004
Level 2 [Member] | Financial Institution Debt Securities [Member]
Marketable securities:
Marketable securities	138,443	40,278
Level 2 [Member] | Corporate Debt Securities [Member]
Marketable securities:
Marketable securities	41,766	18,967
Level 2 [Member] | Other Asset Backed Securities [Member]
Marketable securities:
Marketable securities	$ 11,474	$ 8,499

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 35,274	$ 31,864
Less: accumulated depreciation and amortization	(19,331)	(13,868)
Property and equipment, net	15,943	17,996
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	30,438	27,199
Office Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	1,181	1,121
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	1,076	1,051
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	1,520	1,474
Computer Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 1,059	$ 1,019

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 6,311	$ 5,587	$ 4,464

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Employee compensation and benefits	$ 10,920	$ 6,311
Accrued research and development	11,008	4,208
Accrued legal and professional expenses	1,876	1,563
Accrued other	1,750	1,191
Total accrued expenses	$ 25,554	$ 13,273

Income Taxes - Schedule of Reco

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, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(21.00%)	(21.00%)	(21.00%)
State income taxes	(7.40%)	(8.90%)	(8.60%)
Research and development tax credits	(1.80%)	(5.10%)	(4.70%)
Stock-based compensation	(1.30%)	1.20%	(0.60%)
Change in valuation allowance	31.50%	33.80%	34.90%

Income Taxes - Summary of Compa

Income Taxes - Summary of Company's Net Deferred Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Intangibles, including acquired in-process research and development	$ 981	$ 1,091
Capitalized start-up costs	378	421
Net operating loss carryforwards	101,807	63,245
Research and development credit carryforwards	23,166	19,417
Operating lease liability	10,713	5,008
Deferred revenue	4,680	7,843
Equity-based compensation	8,574	7,092
Accruals and allowances	2,200	1,245
Gross deferred tax assets	152,499	105,362
Deferred tax asset valuation allowance	(140,868)	(98,513)
Total deferred tax assets	11,631	6,849
Deferred tax liabilities:
Fixed assets	(970)	(1,633)
Operating lease right-of-use assets	(10,661)	(5,216)
Total deferred tax liabilities	$ (11,631)	$ (6,849)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	Mar. 27, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Benefit [Line Items]
Net operating loss carryforwards, federal		$ 372,500,000	$ 229,900,000
Taxable Income available for the period the loss was generated		20 years
Percentage of Coronavirus Aid Relief and Economic Security Act removes the limit for taxable years	80.00%
Coronavirus Aid Relief and Economic Security Act allows net operating losses carryback period	5 years
Increase in valuation allowance		$ 42,400,000	34,500,000	$ 28,700,000
Research and development and other credit		23,166,000	19,417,000
Unrecognized tax benefits		$ 0
Operating Loss Carryforward Indefinitely Begins to Expire in 2034 [Member]
Income Tax Benefit [Line Items]
Net operating loss carryover, percentage of taxable income		100.00%
Operating Loss Carryforward Indefinitely [Member]
Income Tax Benefit [Line Items]
Net operating loss carryover, percentage of taxable income		80.00%
Federal [Member]
Income Tax Benefit [Line Items]
Net operating loss carryforwards, expiration date description		begin to expire in 2034
Net operating loss carryforwards, begins to expiring year		2034
Tax credit carryforwards, expiration date description		begin to expire in 2034
Tax credit carryforwards, begins to expiring year		2034
Federal [Member] | Operating Loss Carryforward Indefinitely Begins to Expire in 2034 [Member]
Income Tax Benefit [Line Items]
Net operating loss carryforwards, with expiration date		$ 37,200,000
Federal [Member] | Operating Loss Carryforward Indefinitely [Member]
Income Tax Benefit [Line Items]
Net operating loss carryforwards with no expiration date		335,300,000
Federal [Member] | Tax Carryforwards Begin to Expire in 2034 [Member]
Income Tax Benefit [Line Items]
Tax credit carryforwards, with expiration date		$ 15,000,000	12,600,000
State [Member]
Income Tax Benefit [Line Items]
Net operating loss carryforwards, expiration date description		begin to expire in 2034
Net operating loss carryforwards, begins to expiring year		2034
Research and development and other credit		$ 10,300,000	8,700,000
Research and development tax credits, expiration year		2029
Research and development tax credits, expiration date description		begin to expire in 2029
State [Member] | Operating Loss Carryforward Begin to Expire In 2034 [Member]
Income Tax Benefit [Line Items]
Net operating loss carryforwards, with expiration date		$ 373,100,000	$ 236,800,000

Collaborations - Summary of Cha

Collaborations - Summary of Changes in Accounts Receivable and Contract Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounts receivable:
Accounts receivable, Balance at Beginning of Period	$ 4,620	$ 7,547
Accounts receivable, Additions	103,116	15,999
Accounts receivable, Deductions	(105,606)	(18,926)
Accounts receivable, Balance at End of Period	2,130	4,620
Contract liabilities:
Deferred revenue, Balance at Beginning of Period	28,810	55,932
Deferred revenue, Additions	87,477	4,000
Deferred revenue, Deductions	(42,356)	(31,122)
Deferred revenue, Balance at End of Period	$ 73,931	$ 28,810

Collaborations - Summary of Rev

Collaborations - Summary of Revenues Recognized Resulting From Changes in Contract Liability Balance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue From Contract With Customer [Abstract]
Amounts included in the contract liability at the beginning of the period	$ 11,571	$ 27,122

Collaborations - Additional Inf

Collaborations - Additional Information (Detail)	May 30, 2020USD ($)TargetcapProductAgreement$ / sharesshares	Dec. 13, 2019	Dec. 12, 2019	Jul. 31, 2018USD ($)shares	Apr. 30, 2016USD ($)	Dec. 31, 2020USD ($)$ / shares	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)$ / shares	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)PerformanceObligation$ / shares	Dec. 31, 2019USD ($)$ / shares	Dec. 31, 2018USD ($)	Dec. 31, 2020USD ($)$ / shares	Dec. 31, 2020USD ($)$ / shares
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses incurred to obtain collaboration agreements and costs to fulfill contracts														$ 0
Costs to obtain or fulfill contract capitalized						$ 0								$ 0			$ 0	$ 0
Common stock, par value | $ / shares						$ 0.0001				$ 0.0001				$ 0.0001	$ 0.0001		$ 0.0001	$ 0.0001
Collaboration revenue						$ 6,595,000	$ 22,220,000	$ 16,263,000	$ 12,916,000	$ 10,936,000	$ 10,616,000	$ 11,118,000	$ 10,433,000	$ 57,994,000	$ 43,103,000	$ 30,434,000
Deferred revenue						73,931,000				28,810,000				73,931,000	28,810,000	55,932,000	$ 73,931,000	$ 73,931,000
2020 Regeneron Amendment [Member] | Hemophilia Co Co Agreements
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payment of royalty percentage on net product sales	35.00%
Regeneron [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Stock purchase agreement date	May 30, 2020
Regeneron [Member] | 2016 Regeneron Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue additions					$ 75,000,000									75,000,000
Purchase of common stock through private placement														$ 50,000,000
Number of performance obligations | PerformanceObligation														3
Transaction price														$ 125,000,000
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 [Member] | 2016 Regeneron Agreement [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development based milestone payments under agreement					25,000,000
Regulatory based milestone payments under agreement					110,000,000
Sales based milestone payments under agreement					185,000,000
Regeneron [Member] | Stock Purchase Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Purchase of common stock through private placement					$ 50,000,000
Premium on sale of shares														$ 17,400,000
Fair value recorded in statement of stockholders’ equity upon issuance of shares														12,600,000
Regeneron [Member] | 2020 Regeneron Amendment [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue additions	$ 70,000,000													$ 70,000,000
Collaboration agreement further option extension period														two
Additional regeneron target cap | Targetcap	5
Fee to extend collaboration arrangement	$ 25,000,000
Collaboration term extension period	2024-04
One time collaboration payment	$ 30,000,000
Collaboration term extension period	2 years
Royalty payment obligation expiration period	12 years
Termination period of agreement	180 days
Number of performance obligations | PerformanceObligation														3
Transaction price														$ 110,900,000
Amount allocated to licenses to targets and associated research activities and evaluation plans														91,900,000
Amount allocated to technology collaboration and associated research activities														3,700,000
Cumulative catch up adjustment														8,400,000
Remaining transaction price transferred at inception of arrangement														23,500,000
Transaction price allocated to combined performance obligation														110,900,000
Amount allocated to transfer license to develop factor VIII target for hemophilia A														15,300,000
Regeneron [Member] | 2020 Regeneron Amendment [Member] | Option Exercised to Increase Regeneron Target Cap [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue additions	$ 30,000,000
Regeneron [Member] | 2020 Regeneron Amendment [Member] | Hemophilia Co Co Agreements
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payment of royalty percentage on net product sales	65.00%
Number of agreements entered | Agreement	2
Regeneron [Member] | 2020 Regeneron Amendment [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Increase in regeneron target cap | Targetcap	15
Regeneron [Member] | 2020 Regeneron Amendment [Member] | Maximum [Member] | Non-exclusive License to Regeneron under Certain CRISPR/Cas Platform IP [Member] | CRISPR Product [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of unique ex vivo products commercialized | Product	10
Regeneron [Member] | 2020 Regeneron Amendment [Member] | Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Increase in regeneron target cap | Targetcap	10
Regeneron [Member] | 2020 Stock Purchase Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock shares sold | shares	925,218
Common stock, par value | $ / shares	$ 0.0001
Cash consideration received on sale of common stock	$ 30,000,000
Sale of stock, price per share | $ / shares	$ 32.42
Percentage of premium over volume-weighted average trading price of common stock during 30-day period prior to closing of equity transaction	100.00%
Regeneron [Member] | Co-Development and Co-Promotion Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payment of royalty percentage on net product sales		25.00%	50.00%	50.00%
Termination period of agreement				180 days
Regeneron [Member] | Co-Development and Co-Promotion Agreements [Member] | Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Options exercisable, number of shares exercisable | shares				4
Collaborative arrangement obligation to be fund in development costs				$ 5,000,000
Regeneron [Member] | Regeneron Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue additions																	145,000,000
Collaboration revenue														$ 53,000,000	24,600,000	20,100,000	123,200,000
Aggregate transaction price remaining to be recognized, period														Through December 31, 2020
Payments due														$ 10,700,000	12,000,000	7,500,000
Regeneron [Member] | Regeneron Agreement [Member] | Research and Development Services [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue																	34,800,000
Regeneron [Member] | Regeneron Amendment [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate transaction price remaining to be recognized						73,900,000								73,900,000			73,900,000	73,900,000
Accounts receivable						2,100,000				3,600,000				2,100,000	3,600,000		2,100,000	2,100,000
Deferred revenue						73,900,000				28,800,000				$ 73,900,000	28,800,000		73,900,000	73,900,000
Novartis [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Strategic collaboration agreement amended date														2018-12
Novartis [Member] | Regeneron Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue														$ 5,000,000
Deferred revenue						0				0				0	0		0	0
Accounts receivable						$ 0				$ 1,000,000				0	1,000,000		$ 0	0
Novartis [Member] | Novartis Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue additions																		62,400,000
Collaboration revenue														$ 0	$ 18,500,000	$ 10,300,000		$ 62,400,000
Aggregate transaction price remaining to be recognized, period														Through December 31, 2020

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	1 Months Ended						3 Months Ended		12 Months Ended
	Nov. 30, 2020	Sep. 30, 2020USD ($)	Apr. 30, 2019USD ($)	Mar. 31, 2019	Jan. 31, 2016USD ($)	Oct. 31, 2014USD ($)	Dec. 31, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)ft²USD_per_sqft	Dec. 31, 2019USD ($)
Lessee Lease Description [Line Items]
Increase in operating lease right-of-use assets		$ 400							$ (6,457)	$ (5,728)
Increase in operating lease, liability		$ 400
Operating lease right-of-use assets							$ 39,114		39,114	$ 19,137
Operating lease, liability							$ 39,305		$ 39,305
130 Brookline Street [Member]
Lessee Lease Description [Line Items]
Operating lease, description									In October 2014, the Company entered into an agreement to lease office and laboratory space at 130 Brookline Street (the “130 Brookline Lease”) 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. In April 2019, the Company executed an amendment to the lease to extend the term of the lease for the additional five-year period, through January 2025.
Operating lease expiration						2020-01
Lessee operating lease extended expiration date			Jan. 31, 2025
Operating lease, existence of option to extend						true
Operating lease, options to extend									option to extend the term of the lease for an additional five-year period. In April 2019, the Company executed an amendment to the lease to extend the term of the lease for the additional five-year period, through January 2025.
Operating lease, renewal term			5 years			5 years
Lessee operating sublease option to extend									two options to extend the agreement by one year each, for a total option period of up to two years.
Operating sublease expiration				2021-04
Operating sublease, existence of option to extend				true
Operating lease right-of-use assets			$ 1,300
Operating lease, liability			$ 1,300
130 Brookline Street [Member] | Maximum [Member]
Lessee Lease Description [Line Items]
Operating sublease, renewal term				2 years
130 Brookline Street [Member] | Second Amendment [Member]
Lessee Lease Description [Line Items]
Operating lease, description									In March 2020, the Company entered into a second amendment to the 130 Brookline Lease (the “130 Brookline Lease Second Amendment”). The 130 Brookline Lease Second Amendment amends certain terms of the Company’s existing lease, dated October 21, 2014, as amended on April 5, 2019. The 130 Brookline Lease Second Amendment extends the term of the 130 Brookline Lease by approximately six years through January 31, 2031.
Lessee operating lease extended expiration date									Jan. 31, 2031
Operating lease, existence of option to extend									true
Operating lease, options to extend									an option to extend the lease for two consecutive five-year terms.
Operating lease, renewal term							6 years		6 years
Increase in operating lease right-of-use assets								$ 7,300
Increase in operating lease, liability								$ 7,300
130 Brookline Street [Member] | Other Assets [Member]
Lessee Lease Description [Line Items]
Lease security deposit						$ 300
40 Erie Street [Member]
Lessee Lease Description [Line Items]
Operating lease, description									In January 2016, the Company entered into a ten-year agreement to lease office and laboratory space at 40 Erie Street (the “40 Erie Lease”) 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.
Operating lease, existence of option to extend					true
Operating lease, options to extend									option to extend the term of the lease for an additional three years.
Operating lease, renewal term					3 years
Operating lease, term of contract					10 years
Operating lease, existence of option to terminate					true
Operating lease, option to terminate									option to terminate the lease at the end of the sixth year
Operating lease, terminate term					6 years
40 Erie Street [Member] | Second Amendment [Member]
Lessee Lease Description [Line Items]
Operating lease, description									In November 2020, the Company entered into a second amendment to the 40 Erie Lease (the “40 Erie Lease Second Amendment”). The 40 Erie Street Second Amendment amends certain terms of the Company’s existing lease, dated January 6, 2016, as amended on November 12, 2020. The 40 Erie Lease Second Amendment provides the Company with a right of first offer with respect to any space that becomes available at the 40 Erie Street building, and in consideration for this right the Company has agreed to nullify the option to terminate the lease at the end of the sixth year that was included in the 40 Erie Lease.
Operating lease, existence of option to extend	true
Increase in operating lease right-of-use assets							$ 18,500
Increase in operating lease, liability							$ 18,500
Operating lease, option to terminate									option to terminate the lease at the end of the sixth year
Operating lease, terminate term	6 years
40 Erie Street [Member] | Other Assets [Member]
Lessee Lease Description [Line Items]
Lease security deposit					$ 2,200
Albany Lease [Member]
Lessee Lease Description [Line Items]
Area of space leased | ft²									39,000
Operating lease, description									In March 2020, the Company entered into an agreement to lease approximately 39,000 square feet of office and laboratory space at 281 Albany Street in Cambridge, Massachusetts under an operating lease agreement (the “281 Albany Lease”). The Company’s obligation to pay rent will start on the date that is six months after the commencement date or the date on which the Company occupies the premises, whichever occurs earlier (the “Rent Commencement Date”).
Term of lease							10 years		10 years
Base rent per square foot for first year | USD_per_sqft									99
Base rent per square foot for last year | USD_per_sqft									128.87
Amount receivable on cost of construction and tenant improvement									$ 4,400
Letter of credit							$ 1,900		$ 1,900
Operating lease, existence of option to extend									true
Operating lease, options to extend									The Company has the option to extend the 281 Albany Lease for two successive five-year terms.

Leases - Summary of Lease Costs

Leases - Summary of Lease Costs and Other Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lease cost
Operating lease cost	$ 8,447	$ 7,431
Short-term lease cost	56	53
Variable lease cost	2,918	2,218
Total lease cost	11,421	9,702
Other information
Operating cash flows used for operating leases	7,495	6,476
Operating lease liabilities arising from obtaining right-of-use assets	$ 26,432	$ 2,554
Weighted average remaining lease term	6 years 8 months 12 days	3 years
Weighted average discount rate	5.80%	9.00%

Leases - Schedule of Reconcilia

Leases - Schedule of Reconciliation of Undiscounted Cash Flows for Operating Lease Liabilities / Future Minimum Lease Payments (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Leases [Abstract]
2021	$ 7,803
2022	6,604
2023	6,744
2024	6,934
2025	7,322
Thereafter	13,631
Total lease payments	49,038
Less: imputed interest	(9,733)
Operating lease, liability	$ 39,305

Equity-Based Compensation - Add

Equity-Based Compensation - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Dec. 31, 2020	Jan. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining vesting period	3 years
Number of restricted shares	193,936		193,936	71,875
Weighted Average Grant Date Fair Value per Share, Granted			$ 21.70
Number of shares, cancelled			55,446
Number of shares vested			82,829
Unrecognized equity-based compensation expense related to restricted stock	$ 3,800,000		$ 3,800,000
Number of Shares, Granted			260,336
Acceleration resulted in additional expense			$ 19,903,000	$ 15,091,000	$ 17,046,000
Weighted average grant date fair value per share			$ 9.07	$ 9.21	$ 15.05
Total intrinsic value of stock options exercised			$ 20,300,000	$ 2,300,000	$ 18,000,000
Unrecognized compensation cost related to stock options	$ 33,700,000		$ 33,700,000
Stock options outstanding	6,977,440		6,977,440	5,365,971
Vesting description			performance-based stock options that vest upon obtaining certain scientific, financial and regulatory milestones through 2020.
Potential dilutive securities excluded from computation of diluted net loss per common share			7,171,000	5,438,000	5,147,000
Performance-based options forfeited			523,172
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted shares					71,875
Weighted Average Grant Date Fair Value per Share, Granted	$ 36.89			$ 22.88
Number of Shares, Granted	79,316
Weighted average period of unrecognized compensation costs			2 years 7 months 6 days
Performance Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, cancelled			4
Number of shares vested			2
Unrecognized equity-based compensation expense related to restricted stock	$ 0		$ 0
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining vesting period		3 years
Weighted Average Grant Date Fair Value per Share, Granted		$ 15.05
Number of Shares, Granted		181,020		0
RSUs vested number			58,870
Acceleration resulted in additional expense			$ 300,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of unrecognized compensation costs			2 years 6 months
Performance Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options outstanding	77,916		77,916	213,750
Performance-based options vested			47,916
Potential dilutive securities excluded from computation of diluted net loss per common share				188,750
Performance-based options forfeited			125,834
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining vesting period			3 years
Description of stock options granted under the Plan			Stock options granted under the 2015 Plan generally vest 25% on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years, unless they contain specific performance-based vesting provisions. The maximum term of stock options granted under the 2015 Plan is ten years.
Shares available for future issuance	2,006,412		2,006,412
Percentage of cumulative increase in number of shares for future issuance			4.00%
2015 Plan [Member] | First Anniversary of Original Vesting Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vest percentage on the first anniversary			25.00%
Maximum [Member] | 2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term of stock options granted			10 years

Equity-Based Compensation - Sch

Equity-Based Compensation - Schedule of Equity-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	$ 19,903	$ 15,091	$ 17,046
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	10,202	6,986	8,994
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	$ 9,701	$ 8,105	$ 8,052

Equity-Based Compensation - Sum

Equity-Based Compensation - Summary of Restricted Stock Activity (Detail)	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Unvested, Beginning balance | shares	71,875
Number of Shares, Granted | shares	260,336
Number of Shares, Vested | shares	(82,829)
Number of Shares, Cancelled | shares	(55,446)
Number of Shares, Unvested, Ending balance | shares	193,936
Weighted Average Grant Date Fair Value per Share, Unvested, Beginning balance | $ / shares	$ 22.88
Weighted Average Grant Date Fair Value per Share, Granted | $ / shares	21.70
Weighted Average Grant Date Fair Value per Share, Vested | $ / shares	17.31
Weighted Average Grant Date Fair Value per Share, Cancelled | $ / shares	21.82
Weighted Average Grant Date Fair Value per Share, Unvested, Ending balance | $ / shares	$ 23.98

Equity-Based Compensation - S_2

Equity-Based Compensation - Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	0.80%	2.10%	2.70%
Expected life of options	6 years	6 years	6 years
Expected volatility of underlying stock	67.80%	68.10%	87.10%
Expected dividend yield	0.00%	0.00%	0.00%

Equity-Based Compensation - S_3

Equity-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding, Beginning Balance | shares	5,365,971
Number of options, Granted | shares	2,975,465
Number of options, Exercised | shares	(840,824)
Number of options, Forfeited | shares	(523,172)
Number of Options, Outstanding, Ending Balance | shares	6,977,440
Number of Options, Exercisable | shares	2,950,493
Weighted Average Exercise Price per Share, Outstanding, Beginning Balance | $ / shares	$ 15.67
Weighted Average Exercise Price per Share, Granted | $ / shares	15.04
Weighted Average Exercise Price per Share, Exercised | $ / shares	13.77
Weighted Average Exercise Price per Share, Forfeited | $ / shares	18.41
Weighted Average Exercise Price per Share, Outstanding, Ending Balance | $ / shares	15.43
Weighted Average Exercise Price per Share, Exercisable | $ / shares	$ 15.22
Weighted Average Remaining Contractual Term, Outstanding	7 years 10 months 9 days
Weighted Average Remaining Contractual Term, Exercisable	6 years 7 months 2 days
Aggregate Intrinsic Value, Outstanding | $	$ 271,940
Aggregate Intrinsic Value, Exercisable | $	$ 115,608

Loss Per Share - Schedule of Ba

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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net loss	$ (42,192)	$ (27,840)	$ (32,393)	$ (31,806)	$ (28,276)	$ (23,634)	$ (25,683)	$ (21,940)	$ (134,231)	$ (99,533)	$ (85,343)
Weighted average shares outstanding, basic and diluted	61,306	58,754	53,369	50,491	49,350	48,554	45,814	45,234	55,987	47,247	43,069
Net loss per share, basic and diluted	$ (0.69)	$ (0.47)	$ (0.61)	$ (0.63)	$ (0.57)	$ (0.49)	$ (0.56)	$ (0.49)	$ (2.40)	$ (2.11)	$ (1.98)

Loss Per Share - Potential Dilu

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, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	7,171	5,438	5,147
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	194	72	109
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	6,977	5,366	5,038

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Dec. 04, 2020	Dec. 01, 2020	Jun. 05, 2020	Jun. 01, 2020	May 30, 2020	May 31, 2020	Aug. 31, 2019	Oct. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock, par value									$ 0.0001	$ 0.0001	$ 0.0001
Proceeds from common stock offering											$ 1,117,600
Regeneron [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering									$ 12,580
Issuance of common stock									$ 12,580
2018 Sales Agreement [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares								5,890,648
Common stock price per share								$ 16.98
Proceeds from common stock offering								$ 96,400
Percentage of gross proceeds from common stock as sales agent cash commission								3.00%
2018 Sales Agreement [Member] | General and Administrative Expenses [Member]
Class Of Stock [Line Items]
Legal accounting and other fees								$ 600
2018 Sales Agreement [Member] | Maximum [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering								$ 100,000
2019 Sales Agreement [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares									2,270,161	287,231
Common stock price per share									$ 22.53	$ 16.48	$ 22.53
Proceeds from common stock offering									$ 49,500	$ 4,400
Percentage of gross proceeds from common stock as sales agent cash commission									3.00%
Proceeds from common stock offering									$ 94,100		$ 94,100
2019 Sales Agreement [Member] | General and Administrative Expenses [Member]
Class Of Stock [Line Items]
Legal accounting and other fees									200	$ 200
2019 Sales Agreement [Member] | Maximum [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering							$ 150,000
2020 Stock Purchase Agreement [Member] | Regeneron [Member]
Class Of Stock [Line Items]
Common stock, par value					$ 0.0001
Cash consideration received on sale of common stock					$ 30,000
Sale of stock, price per share					$ 32.42
Percentage of premium over volume-weighted average trading price of common stock during 30-day period prior to closing of equity transaction					100.00%
Follow On Public Offering
Class Of Stock [Line Items]
Proceeds from common stock offering									296,607		$ 438,300
Issuance of common stock									$ 296,607
Follow On Public Offering | Underwriting Agreement [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares		5,513,699		6,301,370
Common stock, par value		$ 0.0001		$ 0.0001
Shares available for future issuance		719,178		821,917
Common stock price per share		$ 36.50		$ 18.25
Proceeds from common stock offering	$ 188,900		$ 107,700
Private Placement [Member] | 2020 Stock Purchase Agreement [Member] | Regeneron [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares						925,218
Common stock, par value						$ 0.0001
Cash consideration received on sale of common stock						$ 30,000
Sale of stock, price per share						$ 32.42
Percentage of premium over volume-weighted average trading price of common stock during 30-day period prior to closing of equity transaction						100.00%
Issuance of common stock						$ 12,600

401(k) Plan - Additional Inform

401(k) Plan - Additional Information (Detail) - 401(k) plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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	$ 1.1	$ 0.8	$ 0.6

Unaudited Quarterly Results - S

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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Data [Abstract]
Collaboration revenue	$ 6,595	$ 22,220	$ 16,263	$ 12,916	$ 10,936	$ 10,616	$ 11,118	$ 10,433	$ 57,994	$ 43,103	$ 30,434
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses:
Research and development	$ 38,231	$ 39,756	$ 37,771	$ 34,650	$ 31,731	$ 27,513	$ 25,460	$ 23,709	$ 150,408	$ 108,413	$ 89,115
General and administrative	10,763	10,566	11,526	11,314	8,976	8,431	13,118	10,533	44,169	41,058	32,189
Total operating expenses	48,994	50,322	49,297	45,964	40,707	35,944	38,578	34,242	194,577	149,471	121,304
Operating loss	(42,399)	(28,102)	(33,034)	(33,048)	(29,771)	(25,328)	(27,460)	(23,809)	(136,583)	(106,368)	(90,870)
Interest income	207	262	641	1,242	1,495	1,694	1,777	1,869	2,352	6,835	5,527
Net loss	$ (42,192)	$ (27,840)	$ (32,393)	$ (31,806)	$ (28,276)	$ (23,634)	$ (25,683)	$ (21,940)	$ (134,231)	$ (99,533)	$ (85,343)
Net loss per share, basic and diluted	$ (0.69)	$ (0.47)	$ (0.61)	$ (0.63)	$ (0.57)	$ (0.49)	$ (0.56)	$ (0.49)	$ (2.40)	$ (2.11)	$ (1.98)
Weighted average shares outstanding, basic and diluted	61,306	58,754	53,369	50,491	49,350	48,554	45,814	45,234	55,987	47,247	43,069