Intellia Therapeutics (NTLA) 10-Q 4 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	NTLA
Entity Registrant Name	INTELLIA THERAPEUTICS, INC.
Entity Central Index Key	0001652130
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		74,419,414
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
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 Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 334,736	$ 160,020
Marketable securities	463,531	437,351
Accounts receivable ($0.2 million and $0 million from related party)	2,491	2,130
Prepaid expenses and other current assets	14,016	17,016
Total current assets	814,774	616,517
Marketable securities - noncurrent	350,451
Property and equipment, net	19,946	15,943
Operating lease right-of-use assets	81,788	39,114
Equity method investment	62,837
Other assets	5,165	4,748
Total Assets	1,334,961	676,322
Current Liabilities:
Accounts payable	7,470	10,460
Accrued expenses	24,633	25,554
Current portion of operating lease liability	8,705	5,696
Current portion of deferred revenue ($34.2 million and $0 million from related party)	56,759	22,544
Total current liabilities	97,567	64,254
Deferred revenue, net of current portion ($28.5 million and $0 million from related party)	63,023	51,387
Long-term operating lease liability	67,273	33,609
Commitments and contingencies (Note 6)
Stockholders’ Equity:
Common stock, $0.0001 par value; 120,000,000 shares authorized; 74,342,178 and 66,234,056 shares issued and outstanding at September 30, 2021 and December 31, 2020, respectively	7	7
Additional paid-in capital	1,729,029	962,173
Accumulated other comprehensive (loss)/income	(174)	1
Accumulated deficit	(621,764)	(435,109)
Total stockholders’ equity	1,107,098	527,072
Total Liabilities and Stockholders’ Equity	$ 1,334,961	$ 676,322

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Accounts receivable, related party	$ 0.2	$ 0
Current portion of deferred revenue, related party	34.2	0
Deferred revenue, net of current portion, related party	$ 28.5	$ 0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	74,342,178	66,234,056
Common stock, shares outstanding	74,342,178	66,234,056

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Collaboration revenue	[1]	$ 7,204	$ 22,220	$ 20,199	$ 51,399
Type of Revenue [Extensible List]		us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses:
Research and development		$ 60,486	$ 39,756	$ 158,646	$ 112,177
General and administrative		18,711	10,566	48,988	33,406
Total operating expenses		79,197	50,322	207,634	145,583
Operating loss		(71,993)	(28,102)	(187,435)	(94,184)
Interest income		349	262	780	2,145
Net loss		$ (71,644)	$ (27,840)	$ (186,655)	$ (92,039)
Net loss per share, basic and diluted		$ (0.97)	$ (0.47)	$ (2.68)	$ (1.70)
Weighted average shares outstanding, basic and diluted		73,706	58,754	69,720	54,218
Other comprehensive loss:
Unrealized loss on marketable securities		$ (161)	$ (124)	$ (175)	$ (230)
Comprehensive loss		$ (71,805)	$ (27,964)	$ (186,830)	$ (92,269)
[1]	Including the following revenue from related party (see Notes 7 and 8):

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Income Statement [Abstract]
Revenue from related party	$ 277	$ 277

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended		77 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (186,655)	$ (92,039)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	5,011	4,709
Equity-based compensation	32,448	14,321
Amortization/(accretion) of investment premiums/(discounts)	4,970	(195)
Changes in operating assets and liabilities:
Accounts receivable	(361)	3,403
Prepaid expenses and other current assets	(5,073)	(1,951)
Operating right-of-use assets	6,761	4,866
Other assets	(248)	348
Accounts payable	(1,870)	3,445
Accrued expenses	(1,170)	6,719
Deferred revenue	(16,986)	50,804
Operating lease liabilities	(7,206)	(4,116)
Net cash used in operating activities	(170,379)	(9,686)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(9,888)	(2,579)
Purchases of marketable securities	(772,759)	(244,790)
Maturities of marketable securities	390,984	243,800
Net cash used in investing activities	(391,663)	(3,569)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock			$ 1,815,700
Proceeds from options exercised	39,868	1,967
Issuance of shares through employee stock purchase plan	970	685
Net cash provided by financing activities	734,408	137,686
Net increase in cash and cash equivalents and restricted cash and cash equivalents	172,366	124,431
Cash and cash equivalents and restricted cash and cash equivalents, beginning of period	164,606	57,226
Cash and cash equivalents and restricted cash and cash equivalents, end of period	336,972	181,657	336,972
Reconciliation of cash and cash equivalents and restricted cash and cash equivalents to condensed consolidated balance sheet:
Cash and cash equivalents	334,736	179,746	334,736
Restricted cash and cash equivalents, included in prepaids and other current assets and other assets	2,236	1,911	2,236
Cash and cash equivalents and restricted cash and cash equivalents, end of period	336,972	181,657	336,972
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Purchases of property and equipment unpaid at period end	633	545
Right-of-use assets acquired under operating leases	49,435	7,939
Non-cash contribution of intellectual property to NewCo	62,900	0
Follow-on Offering [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	648,315	107,732	1,086,900
At The Market Offerings [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	45,255	14,722	$ 196,500
Regeneron Pharmaceuticals Inc. [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	$ 0	$ 12,580

Overview and Basis of Presentat

Overview and Basis of Presentation	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Overview and Basis of Presentation	1. Overview and Basis of Presentation Intellia Therapeutics, Inc. (“Intellia” or the “Company”) is a leading clinical-stage genome editing company, focused on developing novel, potentially curative therapeutics using CRISPR/Cas9 technology. 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”). To fully realize the transformative potential of CRISPR/Cas9, the Company is pursuing two primary approaches. The Company’s in vivo programs use intravenously administered CRISPR as the therapy, in which its proprietary delivery technology enables highly precise editing of disease-causing genes directly within specific target tissues. The Company’s ex vivo programs use CRISPR to create the therapy by using engineered human cells to treat cancer and autoimmune diseases. The Company’s deep scientific, technical and clinical development experience, along with its robust intellectual property (“IP”) portfolio, enables the Company to unlock broad therapeutic applications of CRISPR/Cas9 to create new classes of genetic medicine. The condensed consolidated financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Annual Report on Form 10-K (“Annual Report”) for the year ended December 31, 2020. The unaudited condensed 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 unrealized gain/loss on marketable securities. During the third quarter of 2021, the Company entered into a joint venture with Cellex Cell Professionals GmbH (“Cellex”) and funds managed by Blackstone Life Sciences Advisors L.L.C. (“BXLS”) to establish a new chimeric antigen receptor (“CAR-T”) cell therapy company (“NewCo” ). The Company had a 33.33 % investment share in NewCo at the time of the initial closing and accounts for the investment under the equity method of accounting. Refer to Notes 2 and 8 for further details. The preparation of financial statements in conformity with 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 condensed consolidated financial statements have been made in connection with the calculation of revenues, research and development expenses, equity-based compensation expense and the valuation of our equity method investment. 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 the Company’s 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 condensed consolidated financial statements prospectively from the date of the change in estimate. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. Liquidity Since its inception through September 30, 2021, the Company has raised an aggregate of approximately $ 1,815.7 million to fund its operations, of which $ 276.8 million was through its collaboration agreements, $ 170.5 million was from its initial public offering (“IPO”) and concurrent private placements, $ 1,086.9 million was from follow-on public offerings, $ 196.5 million was from at-the-market offerings and $ 85.0 million was from the sale of convertible preferred stock. In July 2021, the Company closed an underwritten public offering of 4,758,620 shares of common stock at the public offering price of $ 145.00 per share, for aggregate net proceeds of $ 648.3 million after deducting approximately $ 41.7 million in underwriting discounts and offering costs. The Company expects that its cash, cash equivalents and marketable securities as of September 30, 2021 will enable the Company to fund its ongoing operating expenses and capital expenditure requirements for at least the twelve-month period following the issuance of these condensed consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies The Company’s significant accounting policies are described in Note 2, “Summary of Significant Accounting Policies” to the consolidated financial statements included in the Annual Report for the year ended December 31, 2020. There have been no material changes during the nine months ended September 30, 2021, other than as noted below. Variable Interest Entity The Company evaluates at the inception of each arrangement, and whenever a reconsideration event occurs, whether an entity in which the Company holds an investment or in which the Company has other variable interests is considered a variable interest entity (“VIE”) in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 810, Consolidation (“ASC 810”). If the entity meets the criteria to qualify as a VIE, the Company assesses whether or not the Company is the primary beneficiary of that VIE based on a number of factors, including (i) which party has the power to direct the activities that most significantly affect the VIE’s economic performance, (ii) the parties’ contractual rights and responsibilities pursuant to any contractual agreements and (iii) which party has the obligation to absorb losses or the right to receive benefits from the VIE. If the Company is deemed the primary beneficiary of a VIE, the Company consolidates such entity and reflects the non-controlling interest of other beneficiaries of that entity. If the Company is not the primary beneficiary, no consolidation is necessary, and the Company accounts for the investment or other variable interest in accordance with applicable U.S. GAAP. Equity Method of Accounting In circumstances where the Company has the ability to exercise significant influence, but not control, over the operating and financial policies of an entity in which the Company has an investment, the Company utilizes the equity method of accounting for recording related investment activity. In assessing whether the Company exercises significant influence, the Company considers the nature and magnitude of the investment, the voting and protective rights the Company holds, any participation in the governance of the other entity and other relevant factors such as the presence of a collaborative or other business relationship. Under the equity method of accounting, the Company’s investments are initially recorded at cost on the condensed consolidated balance sheets. Upon recording an equity method investment, the Company evaluates whether there are basis differences between the carrying value and fair value of the Company’s proportionate share of the investee’s underlying net assets. Typically, the Company amortizes basis differences identified on a straight-line basis over the underlying assets’ estimated useful lives when calculating the attributable earnings or losses, excluding the basis differences attributable to in-process research and development that had no alternative future use (“IPR&D”). If the Company is unable to attribute all of the basis difference to specific assets or liabilities of the investee, the residual excess of the cost of the investment over the proportional fair value of the investee’s assets and liabilities is considered to be Equity Method Goodwill and is recognized within the equity investment balance, which is tracked separately within the Company’s memo accounts. The Company subsequently records in the condensed consolidated statements of operations and comprehensive income (loss) its share of income or loss of the other entity within other income/expense. If the share of losses exceeds the carrying value of the Company’s investment, the Company will suspend recognizing additional losses and will continue to do so unless it commits to providing additional funding; however, if there are intra-entity profits this can cause the investment balance to go negative. The Company evaluates its equity method investments for impairment whenever events or changes in circumstance indicate that the carrying amounts of such investments may be impaired and considers qualitative and quantitative factors including the investee's financial metrics, product and commercial outlook and cash usage. If a decline in the value of an equity method investment is determined to be other than temporary, a loss is recorded in earnings in the current period and the investment is written down to fair value. At September 30, 2021, the Company accounted for its investment in NewCo under the equity method of accounting and no impairment charges were recognized during the three and nine months ended September 30, 2021. Refer to Note 8 for further details. Recent Accounting Pronouncements – Adopted In December 2019, the FASB issued Accounting Standards Update (“ASU”) 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes . ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The Company adopted ASU 2019-12 on January 1, 2021. The adoption did not have a material effect on the Company’s condensed consolidated financial statements.

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and December 31, 2020 at net book value: September 30, 2021 Amortized Gross Unrealized Gross Unrealized Estimated Fair (In thousands) Marketable securities: U.S. Treasury and other government securities $ 251,302 $ 9 $ ( 69 ) $ 251,242 Financial institution debt securities 395,052 12 ( 66 ) 394,998 Corporate debt securities 32,099 - ( 9 ) 32,090 Other asset-backed securities 135,702 1 ( 51 ) 135,652 Total $ 814,155 $ 22 $ ( 195 ) $ 813,982 December 31, 2020 Amortized Gross Unrealized Gross Unrealized Estimated Fair (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 The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. At September 30, 2021 and December 31, 2020, the balance in the Company’s accumulated other comprehensive (loss) income was composed of activity related to the Company’s available-for-sale marketable securities. There were no realized gains or losses in the nine months ended September 30, 2021 or for the year ended December 31, 2020. The Company did not reclassify any amounts out of accumulated other comprehensive (loss) income during this period. The Company did not have any securities in a material unrealized loss position at September 30, 2021 or December 31, 2020. The Company's available-for-sale securities that are classified as short-term marketable securities in the condensed 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 condensed 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 intend to dispose of within the next twelve months. At September 30, 2021 and December 31, 2020, the Company did no t hold any investments that matured beyond five years of the balance sheet date.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
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 (unadjusted) 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 September 30, 2021 and December 31, 2020, the Company’s financial assets recognized at fair value on a recurring basis consisted of the following: Fair Value as of September 30, 2021 Total Level 1 Level 2 Level 3 (In thousands) Cash equivalents and restricted cash equivalents $ 335,916 $ 335,916 $ - $ - Marketable securities: U.S. Treasury and other government securities 251,242 220,670 30,572 - Financial institution debt securities 394,998 - 394,998 - Corporate debt securities 32,090 - 32,090 - Other asset-backed securities 135,652 - 135,652 - Total marketable securities 813,982 220,670 593,312 - Total $ 1,149,898 $ 556,586 $ 593,312 $ - 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 $ - Certain of the Company’s financial assets, including cash equivalents, restricted 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 September 30, 2021 or December 31, 2020. Other financial instruments, including accounts receivable, accounts payable and accrued expense, are carried at cost, which approximates fair value due to the short duration and term to maturity. The Company’s investment in NewCo was recorded at fair value, determined according to Level 3 inputs in the fair value hierarchy described above. Refer to Note 8 for further details.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses consisted of the following: September 30, December 31, 2021 2020 (In thousands) Employee compensation and benefits $ 11,828 $ 10,920 Accrued research and development 7,873 11,008 Accrued legal and professional expenses 2,561 1,876 Accrued other 2,371 1,750 Total accrued expenses $ 24,633 $ 25,554

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Litigation There have been no material changes to any of the outstanding litigation, nor is the Company a party to any new litigation, since December 31, 2020, except as described below. For further information please see the notes to the consolidated financial statements included in the Company’s Annual Report for the year ended December 31, 2020. 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, known as CB-010, which seeks to develop a CAR-T product directed at CD19. On June 16, 2021, the Company executed a Leaseback Agreement (“Leaseback”) with Caribou, which settled the ongoing arbitration. Under the Leaseback negotiated by the parties, in exchange for an upfront payment, potential future regulatory and sales milestones, and single-digit royalties payable by Caribou, the Company has agreed to leaseback or sublicense certain CRISPR/Cas9 IP, including the Company’s chemical gRNA modification technology and foundational CRISPR/Cas9 IP, to Caribou so that it can develop and commercialize CB-010. Caribou also will be responsible for any payments required in respect of the Company’s in-licensed IP. The Company recorded $ 1.0 million within “Collaboration Revenue” in the second quarter of 2021 on the condensed consolidated statements of operations and comprehensive loss for an upfront payment related to the Leaseback and received the payment in the third quarter of 2021. License Agreements 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 September 30, 2021, the satisfaction and timing of the contingent payments is uncertain and not reasonably estimable.

Collaborations

Collaborations	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaborations	7. Collaborations To accelerate the development and commercialization of CRISPR/Cas9-based products in multiple therapeutic areas, the Company has formed, and intends to seek other opportunities to form, strategic alliances with collaborators who can augment its leadership in CRISPR/Cas9 therapeutic development. As of September 30, 2021, the Company’s accounts receivable and contract liabilities were related to its collaborations with Regeneron Pharmaceuticals, Inc. (“Regeneron”), Novartis Institutes for BioMedical Research, Inc. (“Novartis”) and NewCo. The following table presents changes in the Company’s accounts receivable and contract liabilities during the nine months ended September 30, 2021 and 2020 (in thousands): Balance at Additions Deductions Balance at End Nine Months Ended September 30, 2021 Accounts receivable $ 2,130 $ 5,575 $ ( 5,214 ) $ 2,491 Contract liabilities - Deferred revenue $ 73,931 $ 62,900 $ ( 17,049 ) $ 119,782 Balance at Additions Deductions Balance at End Nine Months Ended September 30, 2020 Accounts receivable $ 4,620 $ 102,203 $ ( 105,606 ) $ 1,217 Contract liabilities - Deferred revenue $ 28,810 $ 87,477 $ ( 36,673 ) $ 79,614 During the nine months ended September 30, 2021 and 2020, the Company recognized the following revenues as a result of changes in the contract liability balance (in thousands): Nine Months Ended September 30, Revenue recognized in the period from: 2021 2020 Amounts included in the contract liability at the beginning of the period $ 16,861 $ 10,249 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. License and Collaboration Agreement 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. At the inception of the 2016 Regeneron Agreement, Regeneron selected the first of its 10 targets, transthyretin (“ATTR”) amyloidosis, which is subject to a co-development and co-promotion agreement between the Company and Regeneron (the “ATTR Co/Co”). On May 30, 2020, the Company entered into (i) amendment no. 1 (the “2020 Regeneron Amendment”) to the 2016 Regeneron Agreement, (ii) co-development and co-funding agreements for the treatment of hemophilia A and hemophilia B (the “Hemophilia Co/Co”) agreements and (iii) a stock purchase agreement. The collaboration expansion builds upon the jointly developed targeted transgene insertion capabilities designed to durably restore a missing therapeutic protein, and to overcome the limitations of traditional gene therapy. The collaboration was extended until April 2024, at which point Regeneron has an option to renew for an additional two years. The 2020 Regeneron Amendment also grants Regeneron exclusive rights to develop products for five additional in vivo CRISPR/Cas-based therapeutic liver targets and non-exclusive rights to independently develop and commercialize up to 10 ex vivo gene edited products made using certain defined cell types. Since December 31, 2020, there have been no material changes to the key terms of the 2016 Regeneron Agreement and the 2020 Regeneron Amendment (the “Amended Agreements”). For further information on the terms and conditions of these agreements, please see the notes to the consolidated financial statements included in the Company’s Annual Report for the year ended December 31, 2020. Revenue Recognition – Collaboration Revenue. Through September 30, 2021, excluding 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 $ 36.6 million for research and development services, primarily under the ATTR Co/Co agreement. Through September 30, 2021 , the Company has recognized $ 141.9 million of collaboration revenue under all arrangements, including $ 6.7 million and $ 18.7 million during the three and nine months ended September 30, 2021, respectively, and $ 22.2 million and $ 46.4 million during the three and nine months ended September 30, 2020, respectively, in the condensed consolidated statements of operations and comprehensive loss. This includes $ 2.1 million and $ 3.9 million during the three and nine months ended September 30, 2021, respectively, and $ 1.2 million and $ 9.8 million during the three and nine months ended September 30, 2020, respectively, primarily representing payments due from Regeneron pursuant to the ATTR Co/Co agreement. These revenues are offset in part by contra-revenue related to the Hemophilia Co/Co agreements amounting to $ 1.1 million and $ 2.1 million during the three and nine months ended September 30, 2021, respectively. As of September 30, 2021, there was approximately $ 57.1 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 September 30, 2021 and December 31, 2020, the Company had accounts receivable of $ 2.1 million related to the Amended Agreements. The Company had deferred revenue of $ 57.1 million and $ 73.9 million as of September 30, 2021 and December 31, 2020, respectively, related to the Amended Agreements. License and Collaboration Agreement with New CAR-T Cell Therapy Company ( “ NewCo ” ) On July 30, 2021 (the “Effective Date”), the Company entered into two agreements with NewCo: (1) a license and collaboration agreement (the “LCA”), under which the Company will collaborate to develop allogeneic universal CAR-T cell therapies and granted NewCo a license to develop and commercialize genome edited universal CAR-T cell therapies (limited to its use with their switchable, universal CAR-T cell UniCAR and RevCAR platforms); and (2) a co-development and co-funding agreement (the “NewCo Co/Co”), under which the Company will co-develop and co-commercialize allogeneic universal CAR-T cell products for an immuno-oncology indication. Scope: The Company granted NewCo an exclusive license to combine the Company’s CRISPR/Cas9 technology platform with NewCo’s switchable, universal CAR-T cell technology platform and made available to NewCo certain know-how and materials. For an eighteen-month period after the Effective Date, the Company will provide to NewCo any improvements with respect to the underlying technology that are developed. For the two-year period immediately following the Effective Date, the Company will perform certain activities, at the Company’s cost and expense, including providing to NewCo certain know-how and materials to enable NewCo to use the Company's CRISPR/Cas9 technology platform, as well as making available employees with requisite knowledge and experience to provide advice and answer questions regarding such know-how and materials for a limited number of hours per year (the “Knowledge Transfer Period”). In addition, the Company and NewCo will collaborate on at least seven universal CAR-T ce ll products that combine the Company's allogeneic T cell technology with NewCo's switchable, universal CAR-T cell technology, referred to as the (“Allo Collaboration”). NewCo will pay the Company to provide supply and manufacturing services for them, including supplying good manufacturing practice CRISPR reagents to support the research and development of all CRISPR Products (as defined in the LCA) under the Allo Collaboration until the completion of the first Pivotal Trial (as defined in the LCA) of the first such CRISPR Product. Financial Terms: In exchange for the license, the Company received a 33.33 % equity interest in NewCo at the time of the initial closing. Governance: The parties formed a joint steering committee (“JSC”), which is responsible for setting research objectives and overseeing the general strategies and research and development activities undertaken by the parties under the LCA. The JSC will meet quarterly until the expiration or termination of the Allo Collaboration. Term and Termination: The term of the Allo Collaboration is from the Effective Date of the LCA until the completion of all activities under the then-current Allo Collaboration with respect to all relevant CRISPR Products. The LCA contains termination provisions, including termination for insolvency, material breach, patent challenge, convenience, and cessation. Co-Development and Co-Promotion Agreement: Under the NewCo Co/Co the parties will co-develop and co-commercialize in the U.S. and key European countries certain allogeneic universal CAR-T products directed to an immuno-oncology target. The Company is the lead commercialization party in the U.S., and NewCo is the lead commercialization party in the European countries. The parties will share equally in the profits and development costs. The Company will have one additional option to enter into a second co-development and co-funding agreement from selected allogeneic universal CAR-T cell therapy products that the parties intend to develop under the Allo Collaboration for a payment of $ 30.0 million to NewCo. Accounting Analysis: The Company concluded that the accounting treatment for the LCA is within the scope of ASU 2014-09, Revenue from Contracts with Customers (Topic 606), and its related amendments (collectively known as “ASC 606”) . The Company evaluated the promised goods and services under the LCA and determined that it included one performance obligation: a combined performance obligation including the license to the allogeneic technology, initial know-how and ongoing support services, including participation in the JSC during the two-year Knowledge Transfer Period. The transaction price was determined to be $ 62.9 million, which represents the fair value of the Company's equity stake in NewCo as of the Effective Date. The Company will allocate the full transaction price to the combined performance obligation including the license to allogeneic technology, the JSC, initial-know-how and ongoing support services. The Company will recognize the $62.9 million using a time elapsed input method over the Knowledge Transfer Period, which in management’s judgement, 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 NewCo. This represents the Company’s best estimate of the obligation, as after this period NewCo will be able to fully benefit from the licensed IP on its own or with readily available resources. Revenue recorded during each period will be eliminated by an amount representing the Company's 33.33 % ownership interest in NewCo at that time, as this represents the intra-entity profit related to the transaction. The Company will re-evaluate the measure of progress in each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. The Company completed the initial transfer of know-how in the third quarter of 2021. The Company recognized $ 125.0 thousand in revenue for the three and nine months ended September 30, 2021 and eliminated $ 62.5 thousand in intra-entity profits, which should be deferred until realized by NewCo. The deferral will be recognized if and when NewCo commercializes a product with the Company's license or abandons the related project. Until such time, the $ 62.5 thousand of revenue is indefinitely deferred and excluded from the results of operations of the Company. As of September 30, 2021 the Company had deferred revenue of $ 62.7 million related to the NewCo LCA. The payments attributable to the supply and manufacturing services are variable and are commensurate with the standalone selling prices of the services, and as such, will be attributed to those services. The Company did not record any consideration related to the supply and manufacturing services during the third quarter of 2021. NewCo Co/Co - Accounting Analysis: The Company concluded that the NewCo Co/Co agreement meets the definition of a collaborative arrangement per ASC 808 , Collaborative Arrangements (“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 NewCo Co/Co as a component of revenues in the condensed 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. The Company has recognized $ 0.2 million in revenues related to the NewCo Co/Co agreement for the three and nine months ended September 30, 2021. 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 CRISPR/Cas9-edited therapies using CAR-T cells and hematopoietic stem cells (“HSCs”). The agreement was amended in December 2018 (the “Novartis Amendment”) to also include research on ocular stem cells (“OSCs”). In December 2019, per the terms of the 2014 Novartis Agreement, the research term ended, although the 2014 Novartis Agreement remains in effect, for which the Company will be eligible to receive milestone and royalty payments in the future. In June 2021, the Company entered into Amendment No. 3 (the “Amendment”) to the 2014 Novartis Agreement. The Amendment amends Novartis’ rights with respect to all of the CAR-T Therapeutic Targets (as defined in the 2014 Novartis Agreement) that Novartis selected under the 2014 Novartis Agreement, including (a) making Novartis’ license non-exclusive for such CAR-T Therapeutic Targets, (b) removing Novartis’ diligence and related reporting obligations for such CAR-T Therapeutic Targets, and (c) refining the scope of Novartis’ sublicense rights for such CAR-T Therapeutic Targets. The Company made a one-time payment to Novartis of $ 10.0 million within 30 days after the effective date of the Amendment, which was recorded as research and development expense in the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2021. Since December 31, 2020, there have been no other material changes to the key terms of the 2014 Novartis Agreement and the Novartis Amendment. For further information on the terms and conditions of these agreements, please see the notes to the consolidated financial statements included in the Company’s Annual Report for the year ended December 31, 2020. Revenue Recognition – Milestone: In March 2020, the U.S. Food and Drug Administration (“FDA”) accepted the investigational new drug (“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 condensed consolidated statement of operations and comprehensive loss. In September 2021, an additional milestone was reached and, as a result, the Company recognized $ 0.3 million as collaboration revenue within the condensed consolidated statement of operations and comprehensive loss. No other milestones under the 2014 Novartis Agreement and the Novartis Amendment were achieved during the three or nine months ended September 30, 2021 or 2020. The Company is eligible to receive additional downstream success-based milestones and royalties. As of September 30, 2021, the Company had a $ 0.3 million account receivable related to the milestone noted above and no deferred revenue related to the 2014 Novartis Agreement and the Novartis Amendment. As of December 31, 2020, the Company had no accounts receivable or deferred revenue related to the 2014 Novartis Agreement and the Novartis Amendment.

Equity-Method Investment

Equity-Method Investment	9 Months Ended
	Sep. 30, 2021
Equity Method Investments and Joint Ventures [Abstract]
Equity-Method Investment	8. Equity-Method Investment On July 30, 2021, the Company finalized a transaction in which the Company, Cellex and BXLS established NewCo, a joint venture and privately held company. In exchange for contributing an exclusive license to the joint venture, the Company entered into a Preferred Stock Purchase Agreement with NewCo for a 33.33 % equity interest in NewCo at the time of the initial closing. Cellex and BXLS each equally owned the remaining 66.67 % at that time. The Company has significant influence over, but does not control, NewCo through its noncontrolling representation on NewCo’s Board of Directors and the Company’s equity interest in NewCo. The Company has determined that the preferred stock it owns is in-substance common stock. The Company is not the primary beneficiary as it does not have the power to direct the activities of NewCo that most significantly impact NewCo’s economic performance. Accordingly, the Company does not consolidate the financial statements of NewCo and accounts for its investment using the equity method of accounting. As of July 30, 2021, the closing date, the fair value of the Company’s investment in NewCo was $ 62.9 million which represents the fair value of the Preferred Stock received in exchange for the exclusive license to the Company’s CRISPR/Cas9 allogeneic platform (See Note 7). In determining the fair value of the Company’s investment, the Company used an option pricing model which requires the input of certain subjective assumptions. The key assumptions used in the option pricing model, which are level 3 inputs, include the anticipated holding period to an exit and liquidity event, the volatility of market participants ( 76 %), the probability of NewCo achieving certain milestones to obtain subsequent financings ( 75 %) and the discount for lack of marketability ( 11 %). Due to the timing and availability of financial information of NewCo, the Company will record its share of losses from NewCo on a quarterly basis on a one-quarter lag from July 30, 2021. Therefore, the Company will record its share of two months of NewCo’s losses generated in the third quarter of 2021 in the Company's operating results in the fourth quarter of 2021. The Company is not aware of any material events or transactions during this period. The Company's initial investment in NewCo was $ 62.9 million. The elimination of the intra-entity profit component of $ 0.1 million (See Note 7) resulted in a reduction in the balance of the investment in NewCo, bringing the carrying value of the investment to $ 62.8 million as of September 30, 2021. The excess of the initial fair value of the Company's investment over the underlying equity in the carrying value of the net assets of NewCo has not yet been allocated. The Company expects to complete the allocation in the fourth quarter of 2021. At September 30, 2021, the maximum exposure to loss is limited to the Company’s equity investment in the joint venture.

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	. Leases 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. In March 2021 the Company determined, in accordance with ASC 842, “Leases (Topic 842)” ( “ ASC 842 ” ), that the commencement date of the lease had been met as the facility was substantially complete and available for use and, accordingly, the Company recognized a right-of-use asset and a lease liability of approximately $ 40.4 million and $ 34.8 million, respectively, in the first quarter of 2021 related to the 281 Albany Lease. In determining the lease liability, the Company used an incremental borrowing rate of 5.52 % based on a number of factors including the Company’s credit rating and the lease term. Included in the recognized right-of-use asset at the inception of the lease was approximately $ 5.6 million in lease payments that were prepaid under the terms of the lease. The base rent under the 281 Albany Lease is $ 99.00 per square foot per year during the first year of the term, which is subject to scheduled annual increases up to $ 128.87 per square foot per year during the last year of the initial term, plus certain operating expenses and taxes. In addition, the landlord agreed to contribute an aggregate of $ 4.4 million toward the cost of construction and tenant improvements for the premises. In accordance with the 281 Albany Lease, the Company is required to maintain a letter of credit in the amount of $ 1.9 million that is restricted for the term of the lease. These restricted cash equivalents are reported in “Other Assets” in the Company’s condensed consolidated balance sheets. The Company has the option to extend the 281 Albany Lease for two successive five-year terms. The option for this extension is not included as part of the lease liability and right-of-use asset at September 30, 2021, as it is not reasonably certain that it will be exercised. In July 2021, the Company entered into an agreement to lease 13,662 square feet of office space at 17 Tudor Street in Cambridge, Massachusetts under an operating lease agreement (the “17 Tudor Lease”). The Company’s obligation to pay rent will start on November 1, 2021. The initial term of the 17 Tudor Lease is five years and the Company has an option to extend the 17 Tudor Lease for one three-year term . The option for this extension is not included as part of the lease liability and right-of-use asset at September 30, 2021, as it is not reasonably certain that it will be exercised. The base rent under the 17 Tudor Lease is $ 74.00 per square foot during the first year of the term, which is subject to scheduled annual increases throughout the term, resulting in a base rent of $ 83.29 per square foot during the last year of the initial term, plus certain operating expenses and taxes. In September 2021 the Company determined, in accordance with ASC 842, that the commencement date of the lease had been met as the Company had gained access to the facility in order to begin work on lessee-owned tenant improvements and, accordingly, the Company recognized a right-of-use asset and a lease liability of approximately $ 4.9 million in the third quarter of 2021 related to the 17 Tudor Lease. In determining the lease liability, the Company used an incremental borrowing rate of 4.15 % based on a number of factors including the Company’s credit rating and the lease term. In accordance with the 17 Tudor Lease, the Company is required to maintain a letter of credit in the amount of $ 0.2 million that is restricted for the term of the lease. These restricted cash equivalents are reported in “Other Assets” in the Company’s condensed consolidated balance sheet. In July 2021, the Company entered into an agreement to extend an existing lease for a clean room located in Waltham, Massachusetts under an operating lease agreement (the “Waltham Lease”) for an additional two years. The Company determined, in accordance with ASC 842, that the extension should be accounted for as a lease modification and, accordingly, recorded an adjustment to the right-of-use asset and lease liability of approximately $ 2.5 million in the third quarter of 2021 related to the Waltham Lease.

Equity-Based Compensation

Equity-Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity-Based Compensation	10. 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 September 30, 2021, there were 3,787,307 shares available for future issuance under the 2015 Plan and the 2016 Employee Stock Purchase Plan. The number of shares reserved for issuance under the 2015 Plan shall be cumulatively increased by four percent of the number of shares of common stock issued and outstanding on the immediately preceding December 31 or such lesser number of shares of common stock as determined by the board of directors. The number of shares reserved for issuance under the 2016 Employee Stock Purchase Plan shall be cumulatively increased by the lesser of a) one percent of the number of shares of common stock issued and outstanding on the immediately preceding December 31, b) 500,000 shares of common stock, or c) such lesser number of shares of common stock as determined by the board of directors. Equity-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive loss as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) Research and development $ 9,017 $ 2,775 $ 18,643 $ 7,325 General and administrative 6,393 2,625 13,805 6,996 Total $ 15,410 $ 5,400 $ 32,448 $ 14,321 Restricted Stock Units RSUs are 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 nine months ended September 30, 2021: Number of Weighted Unvested restricted stock units as of December 31, 2020 193,936 $ 23.98 Granted 354,072 63.13 Vested ( 50,946 ) 17.80 Cancelled ( 53,777 ) 38.02 Unvested restricted stock units as of September 30, 2021 443,285 $ 54.26 In March 2021, the Company granted 259,839 RSUs with a service condition to employees as part of their annual grant, which vest over a period of four years . The weighted average grant date fair value of these RSUs was $ 57.71 . The vesting start date for these RSUs is January 1, 2021. Shares vesting during the nine months ended September 30, 2021 included 26,235 shares that vested in June 2021 as a service condition was met and 21,430 shares that were accelerated in September 2021 based on the Company reaching a performance milestone. Included in the unvested restricted stock as of September 30, 2021 are 42,860 RSUs that include a performance condition in addition to a service condition. These RSUs would vest over a period of 1.2 years and were subject to accelerated vesting based on the Company’s programs achieving certain development milestones before December 1, 2022. In October 2021, these development milestones were achieved and, accordingly, the vesting of the RSUs was accelerated during the fourth quarter of 2021. The fair value of the RSUs at date of grant was $ 15.05 . As of September 30, 2021, there was $ 19.9 million of unrecognized equity-based compensation expense related to restricted stock that is expected to vest. These costs are expected to be recognized over a weighted average remaining vesting period of 2.8 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 $ 105.17 and $ 50.73 per option for those options granted during the three and nine months ended September 30, 2021 and $ 13.38 and $ 8.55 per option for those options granted during the three and nine months ended September 30, 2020, respectively. The total intrinsic value (the amount by which the fair market value exceeded the exercise price) of stock options exercised during the three and nine months ended September 30, 2021 was $ 171.3 million and $ 255.8 million, respectively, and during the three and nine months ended September 30, 2020 was $ 0.9 million and $ 1.7 million, respectively. Weighted average assumptions used to apply this pricing model were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Risk-free interest rate 1.0 % 0.4 % 0.9 % 0.9 % Expected life of options 6.0 years 6.0 years 6.0 years 5.5 - 6.0 years Expected volatility of underlying stock 75.2 % 70.8 % 72.7 % 67.6 % Expected dividend yield 0.0 % 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 the Company’s historical volatility and an average of the historical stock volatilities of several peer companies within the Company’s industry, 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 nine months ended September 30, 2021: Number of Weighted Weighted Aggregate (In years) (In thousands) Outstanding at December 31, 2020 6,977,440 $ 15.43 Granted 2,435,102 79.17 Exercised ( 2,636,437 ) 15.12 Forfeited ( 559,241 ) 29.80 Outstanding at September 30, 2021 6,216,864 $ 39.23 8.01 $ 601,927 Exercisable at September 30, 2021 1,977,984 As of September 30, 2021, there was $ 120.8 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 3.2 years.

Loss Per Share

Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Loss Per Share	11. Loss Per Share The Company calculates basic loss per share by dividing net loss for each respective period by the weighted average number of common shares outstanding for each respective period. The Company computes diluted loss 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. Basic and diluted loss per share was calculated as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) Net loss $ ( 71,644 ) $ ( 27,840 ) $ ( 186,655 ) $ ( 92,039 ) Weighted average shares outstanding, basic 73,706 58,754 69,720 54,218 Net loss per share, basic and diluted $ ( 0.97 ) $ ( 0.47 ) $ ( 2.68 ) $ ( 1.70 ) The following common stock equivalents were excluded from the calculation of diluted loss per share because their inclusion would have been anti-dilutive: Three and Nine Months Ended September 30, 2021 2020 (In thousands) Unvested restricted stock units 443 225 Stock options 6,217 7,527 6,660 7,752

Stockholders_ Equity

Stockholders’ Equity	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Stockholders’ Equity	12. Stockholders’ Equity The following tables present changes in stockholders’ equity for the nine-month periods ended September 30, 2021 and 2020 (in thousands, except share data): Additional Accumulated Other Total Common Paid-In Comprehensive Accumulated Stockholders’ Shares Amount Capital Income (Loss) Deficit Equity Balance at December 31, 2020 66,234,056 $ 7 $ 962,173 $ 1 $ ( 435,109 ) $ 527,072 Issuance of common stock through 52 641,709 - 45,255 - - 45,255 Exercise of stock options 1,014,569 - 13,340 - - 13,340 Equity-based compensation - - 6,424 - - 6,424 Other comprehensive loss - - - ( 13 ) - ( 13 ) Net loss - - - - ( 46,205 ) ( 46,205 ) Balance at March 31, 2021 67,890,334 7 1,027,192 ( 12 ) ( 481,314 ) 545,873 Exercise of stock options 394,801 - 6,163 - - 6,163 Vesting of restricted stock units 26,235 - - - - - Issuance of shares under employee 20,410 - 970 - - 970 Equity-based compensation - - 10,614 - - 10,614 Other comprehensive loss - - - ( 1 ) - ( 1 ) Net loss - - - - ( 68,806 ) ( 68,806 ) Balance at June 30, 2021 68,331,780 7 1,044,939 ( 13 ) ( 550,120 ) 494,813 Issuance of common stock through 284 4,758,620 - 648,315 - - 648,315 Exercise of stock options 1,227,067 - 20,365 - - 20,365 Vesting of restricted stock units 24,711 - - - - - Equity-based compensation - - 15,410 - - 15,410 Other comprehensive loss - - - ( 161 ) - ( 161 ) Net loss - - - - ( 71,644 ) ( 71,644 ) Balance at September 30, 2021 74,342,178 $ 7 $ 1,729,029 $ ( 174 ) $ ( 621,764 ) $ 1,107,098 Additional Accumulated Other Total Common Paid-In Comprehensive Accumulated Stockholders’ Shares Amount Capital Income Deficit Equity Balance at December 31, 2019 50,198,044 $ 5 $ 570,493 $ 261 $ ( 300,878 ) $ 269,881 Issuance of common stock through 48 351,252 - 5,079 - - 5,079 Exercise of stock options 53,579 - 336 - - 336 Equity-based compensation - - 4,157 - - 4,157 Other comprehensive income - - - 112 - 112 Net loss - - - - ( 31,806 ) ( 31,806 ) Balance at March 31, 2020 50,602,875 5 580,065 373 ( 332,684 ) 247,759 Issuance of common stock through 369 6,301,370 1 107,731 - - 107,732 Issuance of common stock in 925,218 - 12,580 - - 12,580 Issuance of common stock through 23 755,848 - 9,643 - - 9,643 Exercise of stock options 83,631 - 1,035 - - 1,035 Issuance of shares under employee 55,296 - 685 - - 685 Equity-based compensation - - 4,764 - - 4,764 Other comprehensive loss - - - ( 218 ) - ( 218 ) Net loss - - - - ( 32,393 ) ( 32,393 ) Balance at June 30, 2020 58,724,238 6 716,503 155 ( 365,077 ) 351,587 Exercise of stock options 67,974 - 597 - - 597 Equity-based compensation - - 5,400 - - 5,400 Other comprehensive loss - - - ( 124 ) - ( 124 ) Net loss - - - - ( 27,840 ) ( 27,840 ) Balance at September 30, 2020 58,792,212 $ 6 $ 722,500 $ 31 $ ( 392,917 ) $ 329,620 Follow-on Offering On June 29, 2021, the Company entered into an underwriting agreement related to a public offering of 4,758,620 shares of its common stock (inclusive of shares sold pursuant to the exercise of the underwriters’ option to purchase additional shares) at a public offering price of $ 145.00 per share. The offering closed on July 2, 2021, for aggregated net proceeds of $ 648.3 million after deducting $ 41.7 million in underwriting discounts and offering costs. At-the-Market Offering Programs In 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. Please refer to the Company’s Annual Report for the year ended December 31, 2020 for additional information regarding these offerings. During the first half of 2021, the Company issued 641,709 shares of its common stock in a series of sales at an average price of $ 72.79 per share in accordance with the 2019 Sales Agreement, for aggregate net proceeds of $ 45.3 million after payment of cash commissions to Jefferies and approximately $ 0.1 million related to legal, accounting and other fees in connection with the sales. There was no activity under the 2019 Sales Agreement in the third quarter of 2021. During the nine months ended September 30, 2020, the Company issued 1,107,100 shares of its common stock in a series of sales at an average price of $ 13.78 per share in accordance with the 2019 Sales Agreement, for aggregate net proceeds of $ 14.7 million after payment of cash commissions to Jefferies and approximately $ 0.1 million related to legal, accounting and other fees in connection with the sales. As of September 30, 2021, $ 47.4 million in shares of common stock remain eligible for sale under the 2019 Sales Agreement.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	13. 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 condensed consolidated financial statements.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events In October 2021, the Company and SparingVision SAS (“SparingVision”), a genomic medicine company developing vision saving treatments for ocular diseases, announced a strategic collaboration to develop novel genomic medicines utilizing CRISPR/Cas9 technology for the treatment of ocular diseases. The Company will grant SparingVision exclusive rights to its proprietary in vivo CRISPR/Cas9-based genome editing technology for up to three ocular targets addressing diseases with significant unmet medical need. SparingVision will lead and fund the preclinical and clinical development for the genome editing product candidates pursued under the collaboration. In addition, the parties will research and develop novel self-inactivating adeno-associated virus (“AAV” ) vectors and lipid nanoparticle-based approaches to address delivery of CRISPR/Cas9 genome editing reagents to the retina. The Company will receive a 10 % equity ownership stake in SparingVision. The Company will also be eligible to receive certain development and commercial milestone payments (up to approximately $ 200 million per product) as well as royalties on potential future sales of products arising from the collaboration. The Company will have an option to obtain exclusive U.S. commercialization rights for product candidates arising from two of three collaboration targets. For product candidates the Company chooses to option, it will pay an opt-in fee, reimburse certain costs, share in 50% of development costs and pay royalties to SparingVision on U.S. sales.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Variable Interest Entity	Variable Interest Entity The Company evaluates at the inception of each arrangement, and whenever a reconsideration event occurs, whether an entity in which the Company holds an investment or in which the Company has other variable interests is considered a variable interest entity (“VIE”) in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 810, Consolidation (“ASC 810”). If the entity meets the criteria to qualify as a VIE, the Company assesses whether or not the Company is the primary beneficiary of that VIE based on a number of factors, including (i) which party has the power to direct the activities that most significantly affect the VIE’s economic performance, (ii) the parties’ contractual rights and responsibilities pursuant to any contractual agreements and (iii) which party has the obligation to absorb losses or the right to receive benefits from the VIE. If the Company is deemed the primary beneficiary of a VIE, the Company consolidates such entity and reflects the non-controlling interest of other beneficiaries of that entity. If the Company is not the primary beneficiary, no consolidation is necessary, and the Company accounts for the investment or other variable interest in accordance with applicable U.S. GAAP.
Equity Method of Accounting	Equity Method of Accounting In circumstances where the Company has the ability to exercise significant influence, but not control, over the operating and financial policies of an entity in which the Company has an investment, the Company utilizes the equity method of accounting for recording related investment activity. In assessing whether the Company exercises significant influence, the Company considers the nature and magnitude of the investment, the voting and protective rights the Company holds, any participation in the governance of the other entity and other relevant factors such as the presence of a collaborative or other business relationship. Under the equity method of accounting, the Company’s investments are initially recorded at cost on the condensed consolidated balance sheets. Upon recording an equity method investment, the Company evaluates whether there are basis differences between the carrying value and fair value of the Company’s proportionate share of the investee’s underlying net assets. Typically, the Company amortizes basis differences identified on a straight-line basis over the underlying assets’ estimated useful lives when calculating the attributable earnings or losses, excluding the basis differences attributable to in-process research and development that had no alternative future use (“IPR&D”). If the Company is unable to attribute all of the basis difference to specific assets or liabilities of the investee, the residual excess of the cost of the investment over the proportional fair value of the investee’s assets and liabilities is considered to be Equity Method Goodwill and is recognized within the equity investment balance, which is tracked separately within the Company’s memo accounts. The Company subsequently records in the condensed consolidated statements of operations and comprehensive income (loss) its share of income or loss of the other entity within other income/expense. If the share of losses exceeds the carrying value of the Company’s investment, the Company will suspend recognizing additional losses and will continue to do so unless it commits to providing additional funding; however, if there are intra-entity profits this can cause the investment balance to go negative. The Company evaluates its equity method investments for impairment whenever events or changes in circumstance indicate that the carrying amounts of such investments may be impaired and considers qualitative and quantitative factors including the investee's financial metrics, product and commercial outlook and cash usage. If a decline in the value of an equity method investment is determined to be other than temporary, a loss is recorded in earnings in the current period and the investment is written down to fair value. At September 30, 2021, the Company accounted for its investment in NewCo under the equity method of accounting and no impairment charges were recognized during the three and nine months ended September 30, 2021. Refer to Note 8 for further details.
Recent Accounting Pronouncements - Adopted	Recent Accounting Pronouncements – Adopted In December 2019, the FASB issued Accounting Standards Update (“ASU”) 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes . ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The Company adopted ASU 2019-12 on January 1, 2021. The adoption did not have a material effect on the Company’s condensed consolidated financial statements.

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and December 31, 2020 at net book value: September 30, 2021 Amortized Gross Unrealized Gross Unrealized Estimated Fair (In thousands) Marketable securities: U.S. Treasury and other government securities $ 251,302 $ 9 $ ( 69 ) $ 251,242 Financial institution debt securities 395,052 12 ( 66 ) 394,998 Corporate debt securities 32,099 - ( 9 ) 32,090 Other asset-backed securities 135,702 1 ( 51 ) 135,652 Total $ 814,155 $ 22 $ ( 195 ) $ 813,982 December 31, 2020 Amortized Gross Unrealized Gross Unrealized Estimated Fair (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

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Summary of Financial Assets Recognized at Fair Value on Recurring Basis	As of September 30, 2021 and December 31, 2020, the Company’s financial assets recognized at fair value on a recurring basis consisted of the following: Fair Value as of September 30, 2021 Total Level 1 Level 2 Level 3 (In thousands) Cash equivalents and restricted cash equivalents $ 335,916 $ 335,916 $ - $ - Marketable securities: U.S. Treasury and other government securities 251,242 220,670 30,572 - Financial institution debt securities 394,998 - 394,998 - Corporate debt securities 32,090 - 32,090 - Other asset-backed securities 135,652 - 135,652 - Total marketable securities 813,982 220,670 593,312 - Total $ 1,149,898 $ 556,586 $ 593,312 $ - 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 $ -

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following: September 30, December 31, 2021 2020 (In thousands) Employee compensation and benefits $ 11,828 $ 10,920 Accrued research and development 7,873 11,008 Accrued legal and professional expenses 2,561 1,876 Accrued other 2,371 1,750 Total accrued expenses $ 24,633 $ 25,554

Collaborations (Tables)

Collaborations (Tables)	9 Months Ended
	Sep. 30, 2021
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 nine months ended September 30, 2021 and 2020 (in thousands): Balance at Additions Deductions Balance at End Nine Months Ended September 30, 2021 Accounts receivable $ 2,130 $ 5,575 $ ( 5,214 ) $ 2,491 Contract liabilities - Deferred revenue $ 73,931 $ 62,900 $ ( 17,049 ) $ 119,782 Balance at Additions Deductions Balance at End Nine Months Ended September 30, 2020 Accounts receivable $ 4,620 $ 102,203 $ ( 105,606 ) $ 1,217 Contract liabilities - Deferred revenue $ 28,810 $ 87,477 $ ( 36,673 ) $ 79,614
Summary of Revenues Recognized Resulting From Changes in Contract Liability Balance	During the nine months ended September 30, 2021 and 2020, the Company recognized the following revenues as a result of changes in the contract liability balance (in thousands): Nine Months Ended September 30, Revenue recognized in the period from: 2021 2020 Amounts included in the contract liability at the beginning of the period $ 16,861 $ 10,249

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Equity-Based Compensation Expense	Equity-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive loss as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) Research and development $ 9,017 $ 2,775 $ 18,643 $ 7,325 General and administrative 6,393 2,625 13,805 6,996 Total $ 15,410 $ 5,400 $ 32,448 $ 14,321
Summary of Restricted Stock Activity	The following table summarizes the Company’s restricted stock activity for the nine months ended September 30, 2021: Number of Weighted Unvested restricted stock units as of December 31, 2020 193,936 $ 23.98 Granted 354,072 63.13 Vested ( 50,946 ) 17.80 Cancelled ( 53,777 ) 38.02 Unvested restricted stock units as of September 30, 2021 443,285 $ 54.26
Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted	Weighted average assumptions used to apply this pricing model were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Risk-free interest rate 1.0 % 0.4 % 0.9 % 0.9 % Expected life of options 6.0 years 6.0 years 6.0 years 5.5 - 6.0 years Expected volatility of underlying stock 75.2 % 70.8 % 72.7 % 67.6 % Expected dividend yield 0.0 % 0.0 % 0.0 % 0.0 %
Summary of Stock Option Activity	The following is a summary of stock option activity for the nine months ended September 30, 2021: Number of Weighted Weighted Aggregate (In years) (In thousands) Outstanding at December 31, 2020 6,977,440 $ 15.43 Granted 2,435,102 79.17 Exercised ( 2,636,437 ) 15.12 Forfeited ( 559,241 ) 29.80 Outstanding at September 30, 2021 6,216,864 $ 39.23 8.01 $ 601,927 Exercisable at September 30, 2021 1,977,984

Loss Per Share (Tables)

Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss Per Share	Basic and diluted loss per share was calculated as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) Net loss $ ( 71,644 ) $ ( 27,840 ) $ ( 186,655 ) $ ( 92,039 ) Weighted average shares outstanding, basic 73,706 58,754 69,720 54,218 Net loss per share, basic and diluted $ ( 0.97 ) $ ( 0.47 ) $ ( 2.68 ) $ ( 1.70 )
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 because their inclusion would have been anti-dilutive: Three and Nine Months Ended September 30, 2021 2020 (In thousands) Unvested restricted stock units 443 225 Stock options 6,217 7,527 6,660 7,752

Stockholders_ Equity (Tables)

Stockholders’ Equity (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Schedule of Changes in Stockholders’ Equity	The following tables present changes in stockholders’ equity for the nine-month periods ended September 30, 2021 and 2020 (in thousands, except share data): Additional Accumulated Other Total Common Paid-In Comprehensive Accumulated Stockholders’ Shares Amount Capital Income (Loss) Deficit Equity Balance at December 31, 2020 66,234,056 $ 7 $ 962,173 $ 1 $ ( 435,109 ) $ 527,072 Issuance of common stock through 52 641,709 - 45,255 - - 45,255 Exercise of stock options 1,014,569 - 13,340 - - 13,340 Equity-based compensation - - 6,424 - - 6,424 Other comprehensive loss - - - ( 13 ) - ( 13 ) Net loss - - - - ( 46,205 ) ( 46,205 ) Balance at March 31, 2021 67,890,334 7 1,027,192 ( 12 ) ( 481,314 ) 545,873 Exercise of stock options 394,801 - 6,163 - - 6,163 Vesting of restricted stock units 26,235 - - - - - Issuance of shares under employee 20,410 - 970 - - 970 Equity-based compensation - - 10,614 - - 10,614 Other comprehensive loss - - - ( 1 ) - ( 1 ) Net loss - - - - ( 68,806 ) ( 68,806 ) Balance at June 30, 2021 68,331,780 7 1,044,939 ( 13 ) ( 550,120 ) 494,813 Issuance of common stock through 284 4,758,620 - 648,315 - - 648,315 Exercise of stock options 1,227,067 - 20,365 - - 20,365 Vesting of restricted stock units 24,711 - - - - - Equity-based compensation - - 15,410 - - 15,410 Other comprehensive loss - - - ( 161 ) - ( 161 ) Net loss - - - - ( 71,644 ) ( 71,644 ) Balance at September 30, 2021 74,342,178 $ 7 $ 1,729,029 $ ( 174 ) $ ( 621,764 ) $ 1,107,098 Additional Accumulated Other Total Common Paid-In Comprehensive Accumulated Stockholders’ Shares Amount Capital Income Deficit Equity Balance at December 31, 2019 50,198,044 $ 5 $ 570,493 $ 261 $ ( 300,878 ) $ 269,881 Issuance of common stock through 48 351,252 - 5,079 - - 5,079 Exercise of stock options 53,579 - 336 - - 336 Equity-based compensation - - 4,157 - - 4,157 Other comprehensive income - - - 112 - 112 Net loss - - - - ( 31,806 ) ( 31,806 ) Balance at March 31, 2020 50,602,875 5 580,065 373 ( 332,684 ) 247,759 Issuance of common stock through 369 6,301,370 1 107,731 - - 107,732 Issuance of common stock in 925,218 - 12,580 - - 12,580 Issuance of common stock through 23 755,848 - 9,643 - - 9,643 Exercise of stock options 83,631 - 1,035 - - 1,035 Issuance of shares under employee 55,296 - 685 - - 685 Equity-based compensation - - 4,764 - - 4,764 Other comprehensive loss - - - ( 218 ) - ( 218 ) Net loss - - - - ( 32,393 ) ( 32,393 ) Balance at June 30, 2020 58,724,238 6 716,503 155 ( 365,077 ) 351,587 Exercise of stock options 67,974 - 597 - - 597 Equity-based compensation - - 5,400 - - 5,400 Other comprehensive loss - - - ( 124 ) - ( 124 ) Net loss - - - - ( 27,840 ) ( 27,840 ) Balance at September 30, 2020 58,792,212 $ 6 $ 722,500 $ 31 $ ( 392,917 ) $ 329,620

Overview and Basis of Present_2

Overview and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended		77 Months Ended
	Jul. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering				$ 1,815,700
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				276,800
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		$ 648,315	$ 107,732	1,086,900
At The Market Offerings [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering		$ 45,255	$ 14,722	$ 196,500
Underwritten Public Offering [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering	$ 648,300
Number of common stock issued upon conversion of shares	4,758,620
Public offering price per share	$ 145
Underwriting discounts and estimated offering costs	$ 41,700
NewCo
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Equity Method Investment, Ownership Percentage		33.33%		33.33%

Marketable Securities - Summary

Marketable Securities - Summary of Available -for-sale Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Amortized Cost	$ 814,155	$ 437,350
Gross Unrealized Gains	22	23
Gross Unrealized Losses	(195)	(22)
Estimated Fair Value	813,982	437,351
U.S. Treasury and Other Government Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	251,302	245,666
Gross Unrealized Gains	9	13
Gross Unrealized Losses	(69)	(11)
Estimated Fair Value	251,242	245,668
Financial Institution Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	395,052	138,445
Gross Unrealized Gains	12	6
Gross Unrealized Losses	(66)	(8)
Estimated Fair Value	394,998	138,443
Corporate Debt Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	32,099	41,765
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(9)	(2)
Estimated Fair Value	32,090	41,766
Other Asset Backed Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	135,702	11,474
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(51)	(1)
Estimated Fair Value	$ 135,652	$ 11,474

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Realized gains or losses on marketable securities	$ 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	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents and restricted cash equivalents	$ 335,916	$ 163,805
Marketable securities:
Marketable securities	813,982	437,351
Total	1,149,898	601,156
U.S. Treasury and Other Government Securities [Member]
Marketable securities:
Marketable securities	251,242	245,668
Financial Institution Debt Securities [Member]
Marketable securities:
Marketable securities	394,998	138,443
Corporate Debt Securities [Member]
Marketable securities:
Marketable securities	32,090	41,766
Other Asset Backed Securities [Member]
Marketable securities:
Marketable securities	135,652	11,474
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents and restricted cash equivalents	335,916	163,805
Marketable securities:
Marketable securities	220,670	241,664
Total	556,586	405,469
Level 1 [Member] | U.S. Treasury and Other Government Securities [Member]
Marketable securities:
Marketable securities	220,670	241,664
Level 2 [Member]
Marketable securities:
Marketable securities	593,312	195,687
Total	593,312	195,687
Level 2 [Member] | U.S. Treasury and Other Government Securities [Member]
Marketable securities:
Marketable securities	30,572	4,004
Level 2 [Member] | Financial Institution Debt Securities [Member]
Marketable securities:
Marketable securities	394,998	138,443
Level 2 [Member] | Corporate Debt Securities [Member]
Marketable securities:
Marketable securities	32,090	41,766
Level 2 [Member] | Other Asset Backed Securities [Member]
Marketable securities:
Marketable securities	$ 135,652	$ 11,474

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Employee compensation and benefits	$ 11,828	$ 10,920
Accrued research and development	7,873	11,008
Accrued legal and professional expenses	2,561	1,876
Accrued other	2,371	1,750
Total accrued expenses	$ 24,633	$ 25,554

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Caribou Leaseback Agreement [Member]
Commitments And Contingencies [Line Items]
Payment related to leaseback	$ 1

Collaborations - Additional Inf

Collaborations - Additional Information (Detail) - USD ($)		1 Months Ended			3 Months Ended		9 Months Ended		66 Months Ended
		Sep. 30, 2021	Jul. 31, 2021	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Jul. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue	[1]				$ 7,204,000	$ 22,220,000	$ 20,199,000	$ 51,399,000
Deferred revenue		$ 119,782,000			119,782,000	79,614,000	119,782,000	79,614,000	$ 119,782,000		$ 73,931,000	$ 28,810,000
Regeneron Pharmaceuticals Inc. [Member] | Regeneron Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue additions									145,000,000
Collaboration revenue					6,700,000	22,200,000	$ 18,700,000	46,400,000	141,900,000
Aggregate transaction price remaining to be recognized, period							Through September 30, 2021
Payments due					2,100,000	$ 1,200,000	$ 3,900,000	$ 9,800,000
Regeneron Pharmaceuticals Inc. [Member] | Regeneron Agreement [Member] | Research and Development Services [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue									36,600,000
Regeneron Pharmaceuticals Inc. [Member] | Regeneron Amendment [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate transaction price remaining to be recognized		57,100,000			57,100,000		57,100,000		57,100,000
Accounts receivable		2,100,000			2,100,000		2,100,000		2,100,000		2,100,000
Deferred revenue		57,100,000			57,100,000		57,100,000		57,100,000		73,900,000
Regeneron Pharmaceuticals Inc. [Member] | Hemophilia Co/Co Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue					1,100,000		$ 2,100,000
Novartis [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Strategic collaboration agreement amended date							2018-12
One time payment to novartis					10,000,000		$ 10,000,000
Novartis [Member] | Regeneron Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue		300,000		$ 5,000,000
Accounts receivable		300,000			300,000		300,000		300,000
Deferred revenue		0			0		0		0		0
Accounts receivable											$ 0
NewCo [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue additions							62,500
Collaboration revenue					125,000		125,000
Deferred revenue		62,700,000			62,700,000		62,700,000		62,700,000
NewCo [Member] | New CAR T-Cell Therapy [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Equity Method Investment, Ownership Percentage										33.33%
NewCo [Member] | Second CoDevelopment and CoPromotion Agreement [Member] | New CAR T-Cell Therapy [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration Payment			$ 30,000,000
NewCo [Member] | NewCo Co/Co Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue					200,000		200,000
Deferred revenue		$ 62,500			$ 62,500		$ 62,500		$ 62,500
Equity Method Investment, Ownership Percentage		33.33%			33.33%		33.33%		33.33%
Collaboration transaction price							$ 62,900,000
[1]	Including the following revenue from related party (see Notes 7 and 8):

Collaborations - Summary of Cha

Collaborations - Summary of Changes in Accounts Receivable and Contract Liabilities (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Accounts receivable:
Accounts receivable, Balance at Beginning of Period	$ 2,130	$ 4,620
Accounts receivable, Additions	5,575	102,203
Accounts receivable, Deductions	(5,214)	(105,606)
Accounts receivable, Balance at End of Period	2,491	1,217
Contract liabilities:
Deferred revenue, Balance at Beginning of Period	73,931	28,810
Deferred revenue, Additions	62,900	87,477
Deferred revenue, Deductions	(17,049)	(36,673)
Deferred revenue, Balance at End of Period	$ 119,782	$ 79,614

Collaborations - Summary of Rev

Collaborations - Summary of Revenues Recognized Resulting From Changes in Contract Liability Balance (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Revenue From Contract With Customer [Abstract]
Amounts included in the contract liability at the beginning of the period	$ 16,861	$ 10,249

Equity-Method Investment - Addi

Equity-Method Investment - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Jul. 30, 2021	Sep. 30, 2021
Schedule of Equity Method Investments [Line Items]
Equity method investment		$ 62,837
Preferred Stock Purchase Agreement [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	33.33%
Preferred Stock Purchase Agreement [Member] | Cellex and BXLS [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	66.67%
NewCo [Member]
Schedule of Equity Method Investments [Line Items]
Investment Owned, at Fair Value	$ 62,900
Intra-entity profit from equity method investments		100
Equity method investment		$ 62,800
NewCo [Member] | Measurement Input, Option Volatility [Member]
Schedule of Equity Method Investments [Line Items]
Equity securities measurement input, percentage	76.00%
NewCo [Member] | Measurement Input Option Subsequent Financing [Member]
Schedule of Equity Method Investments [Line Items]
Equity securities measurement input, percentage	75.00%
NewCo [Member] | Measurement Input, Discount for Lack of Marketability [Member]
Schedule of Equity Method Investments [Line Items]
Equity securities measurement input, percentage	11.00%

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	1 Months Ended	9 Months Ended
	Mar. 31, 2021USD ($)USD_per_sqft	Sep. 30, 2021USD ($)ft²USD_per_sqft	Dec. 31, 2020USD ($)
Lessee Lease Description [Line Items]
Operating lease right-of-use assets		$ 81,788	$ 39,114
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
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
Operating lease right-of-use assets	$ 40,400
Operating lease, liability	$ 34,800
Incremental borrowing rate	5.52%
Prepaid lease payments	$ 5,600
Amount receivable on cost of construction and tenant improvement	4,400
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.
Albany Lease [Member] | Other Assets [Member]
Lessee Lease Description [Line Items]
Letter of credit	$ 1,900
Tudor Lease [Member]
Lessee Lease Description [Line Items]
Area of space leased | ft²		13,662
Operating lease, description		In July 2021, the Company entered into an agreement to lease 13,662 square feet of office space at 17 Tudor Street in Cambridge, Massachusetts under an operating lease agreement (the “17 Tudor Lease”). The Company’s obligation to pay rent will start on November 1, 2021.
Term of lease		5 years
Base rent per square foot for first year | USD_per_sqft		74
Base rent per square foot for last year | USD_per_sqft		83.29
Operating lease right-of-use assets		$ 4,900
Operating lease, liability		$ 4,900
Incremental borrowing rate		4.15%
Operating lease, options to extend		The initial term of the 17 Tudor Lease is five years and the Company has an option to extend the 17 Tudor Lease for one three-year term
Tudor Lease [Member] | Other Assets [Member]
Lessee Lease Description [Line Items]
Letter of credit		$ 200
Waltham Lease [Member]
Lessee Lease Description [Line Items]
Operating lease right-of-use assets		$ 2,500

Equity-Based Compensation - Add

Equity-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining vesting period	4 years
Weighted Average Grant Date Fair Value per Share, Granted				$ 63.13
Number of Shares, Granted				354,072
Additional vesting of shares				50,946
Unrecognized equity-based compensation expense related to restricted stock		$ 19.9		$ 19.9
Weighted average grant date fair value per share		$ 105.17	$ 13.38	$ 50.73	$ 8.55
Total intrinsic value of stock options exercised		$ 171.3	$ 0.9	$ 255.8	$ 1.7
Unrecognized compensation cost related to stock options		$ 120.8		$ 120.8
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Date Fair Value per Share, Granted	$ 57.71
Number of Shares, Granted	259,839
Weighted average period of unrecognized compensation costs				2 years 9 months 18 days
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining vesting period				1 year 2 months 12 days
Weighted Average Grant Date Fair Value per Share, Granted				$ 15.05
Number of Shares, Granted				42,860
Additional vesting of shares				26,235
Accelerated vesting of shares				21,430
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of unrecognized compensation costs				3 years 2 months 12 days
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.
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%
2015 Plan and the 2016 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance		3,787,307		3,787,307
Percentage of cumulative increase in number of shares for future issuance				4.00%
2016 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance		500,000		500,000
Percentage of cumulative increase in number of shares for future issuance				1.00%
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	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	$ 15,410	$ 5,400	$ 32,448	$ 14,321
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	9,017	2,775	18,643	7,325
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Equity-based compensation expense	$ 6,393	$ 2,625	$ 13,805	$ 6,996

Equity-Based Compensation - Sum

Equity-Based Compensation - Summary of Restricted Stock Activity (Detail)	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Unvested, Beginning balance | shares	193,936
Number of Shares, Granted | shares	354,072
Number of Shares, Vested | shares	(50,946)
Number of Shares, Cancelled | shares	(53,777)
Number of Shares, Unvested, Ending balance | shares	443,285
Weighted Average Grant Date Fair Value per Share, Unvested, Beginning balance | $ / shares	$ 23.98
Weighted Average Grant Date Fair Value per Share, Granted | $ / shares	63.13
Weighted Average Grant Date Fair Value per Share, Vested | $ / shares	17.80
Weighted Average Grant Date Fair Value per Share, Cancelled | $ / shares	38.02
Weighted Average Grant Date Fair Value per Share, Unvested, Ending balance | $ / shares	$ 54.26

Equity-Based Compensation - S_2

Equity-Based Compensation - Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.00%	0.40%	0.90%	0.90%
Expected life of options	6 years	6 years	6 years
Expected volatility of underlying stock	75.20%	70.80%	72.70%	67.60%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options				5 years 6 months
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options				6 years

Equity-Based Compensation - S_3

Equity-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding, Beginning Balance	6,977,440
Number of options, Granted	2,435,102
Number of options, Exercised	(2,636,437)
Number of options, Forfeited	(559,241)
Number of Options, Outstanding, Ending Balance	6,216,864
Number of Options, Exercisable	1,977,984
Weighted Average Exercise Price per Share, Outstanding, Beginning Balance	$ 15.43
Weighted Average Exercise Price per Share, Granted	79.17
Weighted Average Exercise Price per Share, Exercised	15.12
Weighted Average Exercise Price per Share, Forfeited	29.80
Weighted Average Exercise Price per Share, Outstanding, Ending Balance	$ 39.23
Weighted Average Remaining Contractual Term, Outstanding	8 years 3 days
Aggregate Intrinsic Value, Outstanding	$ 601,927

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						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss	$ (71,644)	$ (68,806)	$ (46,205)	$ (27,840)	$ (32,393)	$ (31,806)	$ (186,655)	$ (92,039)
Weighted average shares outstanding, basic and diluted	73,706			58,754			69,720	54,218
Net loss per share, basic and diluted	$ (0.97)			$ (0.47)			$ (2.68)	$ (1.70)

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	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	6,660	7,752
Unvested Restricted Stock Units [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	443	225
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	6,217	7,527

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Changes in Stockholders Equity (Detail) - USD ($) $ in Thousands	3 Months Ended						6 Months Ended	9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Class Of Stock [Line Items]
Beginning balance	$ 494,813	$ 545,873	$ 527,072	$ 351,587	$ 247,759	$ 269,881	$ 527,072	$ 527,072	$ 269,881
Beginning balance, shares			66,234,056				66,234,056	66,234,056
Exercise of stock options	20,365	6,163	$ 13,340	597	1,035	336
Exercise of stock options, shares								2,636,437
Issuance of shares under employee stock purchase plan		970			685
Equity-based compensation	15,410	10,614	6,424	5,400	4,764	4,157
Other comprehensive income (loss)	(161)	(1)	(13)	(124)	(218)	112
Net loss	(71,644)	(68,806)	(46,205)	(27,840)	(32,393)	(31,806)		$ (186,655)	(92,039)
Ending balance	$ 1,107,098	494,813	545,873	329,620	351,587	247,759	$ 494,813	$ 1,107,098	329,620
Ending balance, shares	74,342,178							74,342,178
Follow-on Offering [Member]
Class Of Stock [Line Items]
Issuance of common stock	$ 648,315				107,732
At The Market Offerings [Member]
Class Of Stock [Line Items]
Issuance of common stock			45,255		9,643	5,079
Regeneron Pharmaceuticals Inc. [Member] | Private Placement [Member]
Class Of Stock [Line Items]
Issuance of common stock					12,580
Common Stock [Member]
Class Of Stock [Line Items]
Beginning balance	$ 7	$ 7	$ 7	$ 6	$ 5	$ 5	$ 7	$ 7	$ 5
Beginning balance, shares	68,331,780	67,890,334	66,234,056	58,724,238	50,602,875	50,198,044	66,234,056	66,234,056	50,198,044
Exercise of stock options, shares	1,227,067	394,801	1,014,569	67,974	83,631	53,579
Vesting of restricted stock units, shares	24,711	26,235
Issuance of shares under employee stock purchase plan, shares		20,410			55,296
Ending balance	$ 7	$ 7	$ 7	$ 6	$ 6	$ 5	$ 7	$ 7	$ 6
Ending balance, shares	74,342,178	68,331,780	67,890,334	58,792,212	58,724,238	50,602,875	68,331,780	74,342,178	58,792,212
Common Stock [Member] | Follow-on Offering [Member]
Class Of Stock [Line Items]
Issuance of common stock					$ 1
Issuance of common stock, shares	4,758,620				6,301,370
Common Stock [Member] | At The Market Offerings [Member]
Class Of Stock [Line Items]
Issuance of common stock, shares			641,709		755,848	351,252
Common Stock [Member] | Regeneron Pharmaceuticals Inc. [Member] | Private Placement [Member]
Class Of Stock [Line Items]
Issuance of common stock, shares					925,218
Additional Paid-In Capital [Member]
Class Of Stock [Line Items]
Beginning balance	$ 1,044,939	$ 1,027,192	$ 962,173	$ 716,503	$ 580,065	$ 570,493	$ 962,173	$ 962,173	$ 570,493
Exercise of stock options	20,365	6,163	13,340	597	1,035	336
Issuance of shares under employee stock purchase plan		970			685
Equity-based compensation	15,410	10,614	6,424	5,400	4,764	4,157
Ending balance	1,729,029	1,044,939	1,027,192	722,500	716,503	580,065	1,044,939	1,729,029	722,500
Additional Paid-In Capital [Member] | Follow-on Offering [Member]
Class Of Stock [Line Items]
Issuance of common stock	648,315				107,731
Additional Paid-In Capital [Member] | At The Market Offerings [Member]
Class Of Stock [Line Items]
Issuance of common stock			45,255		9,643	5,079
Additional Paid-In Capital [Member] | Regeneron Pharmaceuticals Inc. [Member] | Private Placement [Member]
Class Of Stock [Line Items]
Issuance of common stock					12,580
Accumulated Other Comprehensive Income (Loss) [Member]
Class Of Stock [Line Items]
Beginning balance	(13)	(12)	1	155	373	261	1	1	261
Other comprehensive income (loss)	(161)	(1)	(13)	(124)	(218)	112
Ending balance	(174)	(13)	(12)	31	155	373	(13)	(174)	31
Accumulated Deficit [Member]
Class Of Stock [Line Items]
Beginning balance	(550,120)	(481,314)	(435,109)	(365,077)	(332,684)	(300,878)	(435,109)	(435,109)	(300,878)
Net loss	(71,644)	(68,806)	(46,205)	(27,840)	(32,393)	(31,806)
Ending balance	$ (621,764)	$ (550,120)	$ (481,314)	$ (392,917)	$ (365,077)	$ (332,684)	$ (550,120)	$ (621,764)	$ (392,917)

Stockholders' Equity - Schedu_2

Stockholders' Equity - Schedule of Changes in Stockholders Equity (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020
At The Market Offerings [Member]
Class Of Stock [Line Items]
Stock issuance cost, net		$ 52	$ 23	$ 48
Follow-on Offering [Member]
Class Of Stock [Line Items]
Stock issuance cost, net	$ 284		$ 369

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 02, 2021	Jun. 29, 2021	Aug. 31, 2019	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021
Class Of Stock [Line Items]
Proceeds from common stock offering							$ 1,815,700
Follow-on Offering [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering					$ 648,315	$ 107,732	1,086,900
2019 Sales Agreement [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering					$ 45,300	$ 14,700
Percentage of gross proceeds from common stock as sales agent cash commission					3.00%
Stock Issued During Period Shares New Issues				641,709		1,107,100
Common stock price per share				$ 72.79		$ 13.78
Proceeds from common stock offering					$ 47,400		$ 47,400
2019 Sales Agreement [Member] | General and Administrative Expenses [Member]
Class Of Stock [Line Items]
Legal accounting and other fees					$ 100	$ 100
2019 Sales Agreement [Member] | Maximum [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering			$ 150,000
Underwriting Agreement [Member] | Follow-on Offering [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering	$ 648,300
Stock Issued During Period Shares New Issues		4,758,620
Common stock price per share		$ 145
Underwriting discounts and estimated offering costs	$ 41,700

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - Sparing Vision [Member] - Subsequent Event [Member] $ in Millions	1 Months Ended
	Oct. 31, 2021USD ($)
Subsequent Event [Line Items]
Equity method investment, ownership percentage	10.00%
Development and commercial milestone payment to be received	$ 200
Collaboration description	For product candidates the Company chooses to option, it will pay an opt-in fee, reimburse certain costs, share in 50% of development costs and pay royalties to SparingVision on U.S. sales.