Relay Therapeutics (RLAY) 10-K 25 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 23, 2021	Jul. 20, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Registrant Name	RELAY THERAPEUTICS, INC.
Entity Central Index Key	0001812364
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 2,543,277,454
ICFR Auditor Attestation Flag	false
Entity Common Stock, Shares Outstanding		90,399,972
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	RLAY
Security Exchange Name	NASDAQ
Entity File Number	001-39385
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-3923475
Entity Address, Address Line One	399 Binney Street
Entity Address, Address Line Two	2nd Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	370-8837
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE The registrant intends to file a definitive proxy statement pursuant to Regulation 14A relating to the 2021 Annual Meeting of Stockholders within 120 days of the end of the registrant’s fiscal year ended December 31, 2020. Portions of such definitive proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 447,646	$ 41,954
Investments	230,415	313,862
Accounts receivable	75,000
Contract asset	7,654
Prepaid expenses and other current assets	9,385	4,720
Total current assets	770,100	360,536
Property and equipment, net	6,250	8,094
Operating lease assets	22,579	23,560
Restricted cash	878	878
Other assets	22
Total assets	799,829	393,068
Current liabilities:
Accounts payable	6,351	6,991
Accrued expenses and other current liabilities	5,760	3,746
Operating lease liabilities, current	1,521	1,249
Total current liabilities	13,632	11,986
Operating lease liabilities, net of current portion	22,901	23,583
Restricted stock liability	3	156
Total liabilities	36,536	35,725
Commitments and contingencies (Note 13)
Convertible preferred stock (Series A, B and C), $0.001 par value; no shares authorized as of December 31, 2020 and 337,272,859 shares authorized as of December 31, 2019; no shares issued and outstanding as of December 31, 2020 and 212,642,857 shares issued and outstanding (aggregate liquidation preference of $519,825) as of December 31, 2019		537,781
Stockholders’ equity (deficit):
Common stock, $0.001 par value; 150,000,000 and 260,000,000 shares authorized at December 31, 2020 and December 31, 2019, respectively; 89,991,324 and 4,716,634 shares issued at December 31, 2020 and December 31, 2019, respectively; 89,906,835 and 4,037,476 shares outstanding at December 31, 2020 and December 31, 2019, respectively	90	4
Additional paid-in capital	1,167,367	8,715
Accumulated other comprehensive income	64	325
Accumulated deficit	(404,228)	(189,482)
Total stockholders’ equity (deficit)	763,293	(180,438)
Total liabilities, convertible preferred stock, and stockholders’ equity (deficit)	$ 799,829	$ 393,068

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Preferred stock shares authorized		337,272,859
Preferred stock shares issued		212,642,857
Preferred stock shares outstanding	0	212,642,857
Common stock par value	$ 0.001	$ 0.001
Common stock shares authorized	150,000,000	260,000,000
Common stock shares issued	89,991,324	4,716,634
Common stock shares outstanding	89,906,835	4,037,476
Convertible Preferred Stock [Member]
Temporary equity par value	$ 0.001	$ 0.001
Temporary equity shares authorized	0	337,272,859
Temporary equity shares issued	0	212,642,857
Temporary equity shares outstanding	0	212,642,857
Temporary equity liquidation preference		$ 519,825
Undesignated Preferred Stock [Member]
Preferred stock par value	$ 0.001	$ 0.001
Preferred stock shares authorized	10,000,000	0
Preferred stock shares issued	0	0
Preferred stock shares outstanding	0	0

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue:
Revenue from contract with customer	$ 82,654
Revenue from Contract with Customer, Product and Service [Extensible List]	rlay:LicenseRevenueMember
Total revenue	$ 82,654
Operating expenses:
Research and development expenses	99,862	$ 70,306
General and administrative expenses	38,588	13,742
Total operating expenses	138,450	84,048
Loss from operations	(55,796)	(84,048)
Other income (expense):
Interest income	3,400	8,801
Other expense	(16)	(58)
Total other income (expense), net	3,384	8,743
Net loss	(52,412)	(75,305)
Deemed dividend resulting from extinguishment upon modification of Series C preferred stock	(177,789)
Net loss attributable to common stockholders	$ (230,201)	$ (75,305)
Net loss attributable to common stockholders per share, basic and diluted	$ (5.40)	$ (21.82)
Weighted average shares of common stock, basic and diluted	42,619,582	3,450,500
Other comprehensive income (loss):
Unrealized holding gain (loss)	$ (261)	$ 325
Total other comprehensive income (loss)	(261)	325
Total comprehensive loss	$ (52,673)	$ (74,980)

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Total	Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2018	$ (110,927)	$ 532,120	$ 3	$ 3,247		$ (114,177)
Beginning balance, shares at Dec. 31, 2018		210,863,764	2,998,017
Issuance of Series C convertible preferred stock, net of issuance costs of $50		$ 5,661
Issuance of Series C convertible preferred stock, net of issuance costs of $50, shares		1,779,093
Issuance of common stock upon exercise of stock options	613			613
Issuance of common stock upon exercise of stock options, shares			178,969
Vesting of restricted common stock	400		$ 1	399
Vesting of restricted common stock ,shares			860,490
Stock-based compensation expense	4,456			4,456
Unrealized gain (loss) on investments	325				$ 325
Net loss	(75,305)					(75,305)
Ending balance at Dec. 31, 2019	(180,438)	$ 537,781	$ 4	8,715	325	(189,482)
Ending balance, shares at Dec. 31, 2019		212,642,857	4,037,476
Extinguishment upon modification of Series C preferred stock	(177,789)	$ 177,789		(15,455)		(162,334)
Conversion of convertible preferred stock into common stock upon initial public offering	715,570	$ (715,570)	$ 62	715,508
Conversion of convertible preferred stock into common stock upon initial public offering, shares		(212,642,857)	61,992,534
Issuance of common stock in public offering, net of discounts and issuance costs of $34,707	425,293		$ 23	425,270
Issuance of common stock in public offering, net of discounts and issuance costs of $34,707, shares			23,000,000
Issuance of common stock upon exercise of stock options	$ 1,216			1,216
Issuance of common stock upon exercise of stock options, shares	297,000		297,000
Vesting of restricted common stock	$ 154		$ 1	153
Vesting of restricted common stock ,shares			579,825
Stock-based compensation expense	31,960			31,960
Unrealized gain (loss) on investments	(261)				(261)
Net loss	(52,412)					(52,412)
Ending balance at Dec. 31, 2020	$ 763,293		$ 90	$ 1,167,367	$ 64	$ (404,228)
Ending balance, shares at Dec. 31, 2020			89,906,835

Consolidated Statements of Co_2

Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit (parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Net of discounts and issuance costs	$ 34,707
Convertible Preferred Stock [Member]
Issuance costs net		$ 50

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (52,412)	$ (75,305)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	31,960	4,456
Depreciation expense	3,549	2,845
Net amortization of premiums and discounts on investments	(416)	(2,495)
Loss on sale of equipment		56
Changes in assets and liabilities:
Prepaid expenses and other current assets	(4,665)	(2,123)
Lease assets and liabilities, net	571	1,233
Accounts payable	(410)	3,000
Accrued expenses and other liabilities	2,010	2,200
Accounts receivable	(75,000)
Contract asset	(7,654)
Other assets	(22)
Net cash used in operating activities	(102,489)	(66,133)
Cash flows from investing activities:
Purchases of property and equipment	(1,931)	(8,002)
Proceeds from sale of equipment		20
Purchases of investments	(266,455)	(553,517)
Proceeds from maturities of investments	350,058	242,475
Net cash provided by (used in) investing activities	81,672	(319,024)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs		4,993
Proceeds from issuance of common stock upon exercise of stock options	1,216	613
Proceeds from issuance of common stock upon initial public offering	427,800
Offering costs paid	(2,507)
Net cash provided by financing activities	426,509	5,606
Net increase (decrease) in cash, cash equivalents and restricted cash	405,692	(379,551)
Cash, cash equivalents and restricted cash at beginning of period	42,832	422,383
Cash, cash equivalents and restricted cash at end of period	448,524	42,832
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment additions included in accounts payable and accrued expenses	519	745
Reclassification of restricted stock liability to additional paid-in capital	153	400
Extinguishment upon modification of Series C preferred stock	(177,789)
Conversion of preferred stock into common stock upon initial public offering	715,508
Right of use asset obtained in exchange for lease obligation	$ 819	$ 24,936

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Restricted Cash And Cash Equivalents At Carrying Value [Abstract]
Cash and cash equivalents	$ 447,646	$ 41,954
Restricted cash	878	878
Total cash, cash equivalents and restricted cash as shown on consolidated statements of cash flows	$ 448,524	$ 42,832

Nature of Business and Basis of

Nature of Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2020
Text Block [Abstract]
Nature of Business and Basis of Presentation	1. Nature of Business and Basis of Presentation Relay Therapeutics, Inc. (the “Company”) was incorporated in Delaware on May 4, 2015 and is headquartered in Cambridge, Massachusetts. The Company is a clinical-stage, precision medicines company transforming the drug discovery process with an initial focus on enhancing small molecule therapeutic discovery in targeted oncology. The Company is built upon unparalleled insights into protein motion and how this dynamic behavior relates to protein function. The Company’s Dynamo platform integrates an array of leading edge experimental and computational approaches, which allows the Company to apply the understanding of protein structure and motion to drug discovery. The Company is advancing its pipeline of medicines to address targets in precision oncology, including its lead product candidates, RLY-4008 and RLY-1971, as well as its PI3Kα mutant selective program, known as the RLY-PI3K1047 program. The Company initiated a Phase 1 clinical trial for RLY-1971 in patients with advanced solid tumors in the first quarter of 2020 and a first-in-human clinical trial of RLY-4008 enriched for patients with advanced solid tumors having oncogenic FGFR2 alterations in the third quarter of 2020. In December 2020, the Company entered into the Collaboration and License Agreement (the “Genentech Agreement”) with Genentech, Inc. (“Genentech”), a member of the Roche Group, for the development and commercialization of RLY-1971, as further discussed in Note 5. The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive pre-clinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities. The Company’s product candidates are in development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants. The Company has devoted substantially all of its resources to developing its product candidates, including RLY-1971 and RLY-4008, and the RLY-PI3K1047 program by developing its innovative, experimental and computational approaches on protein motion, building its intellectual property portfolio, business planning, raising capital and providing general and administrative support for these operations. The Company has incurred net operating losses since inception and had an accumulated deficit of $404,228 as of December 31, 2020. The Company expects that its existing cash, cash equivalents and investments as of December 31, 2020, together with the upfront payment of $75,000 received in January 2021 from Genentech under the Genentech Agreement discussed in Note 5, will enable it to fund its planned operating expenses and capital expenditure requirements for at least one year from the date of the issuance of these consolidated financial statements. The future viability of the Company is dependent on its ability to generate cash from operating activities or to raise additional capital to finance its operations. The Company’s failure to raise capital as and when needed could have a material adverse effect on its financial condition and ability to pursue its business strategies. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into license or collaboration arrangements or obtain government grants. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. In the event the Company requires additional funding, there can be no assurance that it will be successful in obtaining sufficient funding on terms acceptable to the Company to fund its continuing operations, if at all. Initial Public Offering On July 20, 2020, the Company closed its initial public offering (“IPO”) and issued 23,000,000 shares of its common stock at a price of $20.00 per share for net proceeds of $425,293, after deducting underwriting discounts and commissions of $32,200 and expenses of $2,507. In connection with the IPO, all shares of Series A, Series B and Series C convertible preferred stock converted into 61,992,534 shares of common stock. Reverse Stock Split On July 8, 2020, the Company’s stockholders approved a decrease in the number of authorized shares of common stock from 260,000,000 to 150,000,000. The Company also effected a one-for-3.55092 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s preferred stock. Accordingly, all share and per share amounts for all periods presented in the accompanying financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the preferred stock conversion ratios.

Significant Accounting Policie

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Significant Accounting Policies	2. Significant Accounting Policies Basis of presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) for reporting on Form 10-K. The Company’s consolidated financial statements include the accounts of Relay Therapeutics, Inc. and its wholly-owned subsidiary, Relay Therapeutics Securities Corporation. All intercompany balances and transactions have been eliminated. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development and manufacturing expenses, the valuation of equity instruments, the determination of the transaction price and standalone selling price of performance obligations under Accounting Standards Codification Topic 606, Revenue from Contracts with Customers The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses, clinical trials and research and development costs, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain or treat COVID-19, as well as the economic impact on local, regional, national and international markets. The Company has made estimates of the impact of COVID-19 within its financial statements and there may be changes to those estimates in future periods. Actual results could differ from the Company’s estimates. Segment Information The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on using innovative experimental and computational approaches on protein motion for making medicines against intractable precision medicine targets. The Company operates in the United States and all tangible assets are held in the United States. Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market funds, are stated at fair value. Restricted Cash The Company had restricted cash of $878 as of December 31, 2020 and 2019 to secure a letter of credit in connection with the lease of the Company’s facilities (see Note 14). The Company classified the restricted cash as a noncurrent asset on its consolidated balance sheets. Investments Investments in marketable securities are classified as available-for-sale. Available-for-sale securities are measured and reported at fair value using quoted prices in active markets for similar securities. Unrealized gains and losses on available-for-sale securities are reported as a separate component of stockholders’ equity (deficit). Premiums or discounts from par value are amortized to investment income over the life of the underlying investment. All of the Company’s available-for-sale securities are available to the Company for use in current operations. As a result, the Company classified all of these securities as current assets even though the stated maturity of some individual securities may be one year or more beyond the balance sheet date. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the consolidated statements of operations and comprehensive loss. If any adjustment is required to reflect a decline in the value of the investment that the Company considers to be “other than temporary”, the Company recognizes a charge to the consolidated statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented. Concentration of Credit Risk and Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. From time to time, the Company has maintained all of its cash, cash equivalents and investments at certain accredited financial institutions in amounts that exceed federally insured limits. The Company generally invests its excess capital in money market funds, U.S. treasury bonds, U.S. treasury bills and agency bonds are subject to minimal credit and market risk. Management has established guidelines relative to credit ratings and maturities intended to safeguard principal balances and maintain liquidity. The investment portfolio is maintained in accordance with the Company’s investment policy, which defines allowable investments, specifies credit quality standards and limits the credit exposure of any single issuer. The Company is dependent on third-party suppliers for research and development activities of its programs, including preclinical and clinical testing. In particular, the Company relies and expects to continue to rely on a small number of these suppliers, including D. E. Shaw Research, LLC as discussed in Note 13, to meet its requirements for its programs. These programs could be adversely affected by a significant interruption in pre-clinical and clinical testing and the supply of active pharmaceutical ingredients and formulated drugs. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. Revenue Recognition The Company accounts for revenue recognition in accordance with Accounting Standards Codification Topic (“ASC”) 606, Revenue from Contracts with Customers At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within the contract and determines those that are performance obligations. The Company then determines the transaction price and allocates it to the performance obligations using the relative selling price model. As part of the accounting for these arrangements, the Company must use significant judgment to determine: (a) the number of performance obligations based on the determination under step (ii) above; (b) the transaction price under step (iii) above, including the determination of whether milestones or other variable consideration should be included in the transaction price; and (c) the stand-alone selling price for each performance obligation identified in the contract for the allocation of the transaction price in step (iv) above. The Company utilizes key assumptions and judgments to determine the stand-alone selling price for each performance obligation, which may include discounted cash flow models, evaluation of comparable transactions, pricing considered in negotiating the transaction and estimated costs, to determine how the transaction price is allocated among the performance obligations Once the performance obligations are identified, the transaction price is allocated to each performance obligation based on the relative stand-alone selling price. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied, either at a point in time or over time. If the performance obligation is satisfied over time, the Company recognizes revenue based on the use of either an output or input method. As of December 31, 2020, the Company had one collaboration and license agreement with Genentech, which the Company entered into on December 11, 2020. For a discussion of the accounting related to the Genentech Agreement, see Note 5, Collaboration and License Arrangement with Genentech Lease Agreements Under ASC 842, Leases Right-of-use assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an estimate of its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. Operating lease right-of-use assets also include the effect of any lease payments made prior to commencement and excludes lease incentives. The lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which are accounted for as a combined element. Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the useful life of the asset. Laboratory and computer equipment are depreciated over three years. Furniture and fixtures are depreciated over five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the related asset. Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations. Impairment of Long-Lived Assets The Company continually evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured in an amount by which the book values of the assets exceed their fair value. The Company did not recognize any impairment losses for the years ended December 31, 2020 and 2019. Classification and Accretion of Convertible Preferred Stock The Company’s convertible preferred stock was classified outside of stockholders’ equity (deficit) on the consolidated balance sheet because the holders of such shares had liquidation rights in the event of a deemed liquidation that, in certain situations, were not solely within the control of the Company and would require the redemption of the then-outstanding convertible preferred stock. The convertible preferred stock was not currently redeemable, except in the event of a deemed liquidation (see Note 8). Because the occurrence of a deemed liquidation event was not probable, the carrying value of the convertible preferred stock was not accreted to their redemption values. Subsequent adjustments to the carrying values of the convertible preferred stock would have been made only when a deemed liquidation event became probable. Upon the closing of the Company’s IPO in July 2020, all outstanding convertible preferred stock automatically converted into 61,992,534 shares of common stock. Stock-Based Compensation The Company measures stock options and other stock-based awards granted to employees, directors and non-employees based on their fair value on the date of grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award. The Company recognizes the impact of forfeitures on stock-based compensation expense as forfeitures occur. The Company issued certain options with performance-based vesting conditions whereby the service inception date preceded the accounting grant date and therefore applied variable accounting for the awards until the fair value of the awards was known on the accounting grant date. The board of directors approved the commencement of vesting for all such awards in 2020, therefore the Company no longer applies variable accounting as of December 11, 2020. The Company estimates the fair value of each stock option grant on the date of grant using the Black-Scholes option-pricing model, which uses as inputs the fair value of the Company’s common stock and assumptions the Company makes for the volatility of its common stock, the expected term of the stock options, the risk-free interest rate for a period that approximates the expected term of the stock options and the expected dividend yield. Prior to the Company’s IPO, the estimated fair value of its common stock was determined by the board of directors, or compensation committee thereof, as of the date of each option grant, with input from management, considering the most recently available third-party valuations of common stock and the board of directors’ assessment of additional objective and subjective factors that it believed were relevant and which may have changed from the date of the most recent valuation through the date of the grant. Historically, these independent third-party valuations of the Company’s equity instruments were performed contemporaneously with identified value inflection points. These third-party valuations were performed in accordance with the guidance outlined in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation Following the Company’s IPO, in connection with the accounting for granted stock options and other awards the Company may grant, the fair value of the Company’s common stock is determined based on the quoted market price of its common stock. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses include salaries, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including allocated facility-related expenses and external costs of outside vendors engaged to conduct both pre-clinical studies and clinical trials. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made. Research and Manufacturing Contracts The Company has entered into various research and development contracts with research institutions and other companies whose costs are included in research and development expense in the accompanying consolidated statements of operations and comprehensive loss. These agreements are generally cancelable and related payments are recorded as research and development expenses as the underlying services are performed. When evaluating the adequacy of the expense recognized, the Company analyzes progress of the services, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the expense recognized and the related prepaid or accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical estimates have not been materially different from the actual costs. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses. Income Taxes The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company’s financial statements or tax returns. Under this method, deferred tax assets and liabilities are determined based on differences between the financial statement carrying amounts and the tax bases of the assets and liabilities using the enacted tax rates in effect in the years in which the differences are expected to reverse. A valuation allowance against deferred tax assets is recorded if, based on the weight of the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2020 and 2019, other comprehensive income (loss) consisted of changes in unrealized gains and losses from available-for-sale investments. Net Loss Per Common Share Basic net loss per share is computed using the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed using the sum of the weighted average number of common shares outstanding during the period and the effect of dilutive securities. The Company applies the two-class method to calculate its basic and diluted net loss per share as the Company has issued shares that meet the definition of participating securities. The two-class method is an earnings allocation formula that treats a participating security as having rights to earnings that otherwise would have been available to common stockholders. The Company’s participating securities contractually entitle the holders of such shares to participate in dividends; but do not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such participating securities. Additionally, in periods in which the Company reports a net loss, diluted net loss per share is the same as basic net loss per share, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. For additional discussion of net loss per common share, please see Note 12, Net Loss Per Share. Recently Adopted Accounting Pronouncements The Company adopted Accounting Standards Update (“ASU”) No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement Recently Issued Accounting Pronouncements Not Yet Adopted In June 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates In August 2020, the FASB issued ASU No. 2020-06, Debt – Debt with Conversion and Other Options and Derivatives and Hedging—Contracts in Entity’s Own Equity In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that the Company adopts as of the specified effective date. The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected to use the extended transition period related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different effective dates for public and nonpublic companies, the Company can adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and can do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company.

Fair Value of Financial Assets

Fair Value of Financial Assets	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets	3. Fair Value of Financial Assets The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of December 31, 2020: Level 1 Level 2 Level 3 Total Assets Cash equivalents: Money market funds $ 447,146 $ — $ — $ 447,146 Investments: US treasury bills — 33,026 — 33,026 US agency securities — 197,389 — 197,389 Total investments — 230,415 — 230,415 Total $ 447,146 $ 230,415 $ — $ 677,561 Fair Value Measurements as of December 31, 2019: Level 1 Level 2 Level 3 Total Assets Cash equivalents: Money market funds $ 41,658 $ — $ — $ 41,658 Investments: US treasury bills — 232,604 — 232,604 US agency securities — 81,258 — 81,258 Total investments — 313,862 — 313,862 Total $ 41,658 $ 313,862 $ — $ 355,520 In determining the fair value of its investments at each date presented above, the Company relied on quoted prices for similar securities in active markets or using other inputs that are observable or can be corroborated by observable market data. The Company did not have any financial assets or liabilities during any of the periods presented in the accompanying consolidated financial statements that required Level 3 inputs.

Investments

Investments	12 Months Ended
	Dec. 31, 2020
Schedule Of Investments [Abstract]
Investments	4. Investments The fair value of available-for-sale investments by type of security was as follows: December 31, 2020 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Investments: U.S treasury bills $ 29,997 $ 21 $ — $ 30,018 U.S agency securities 20,996 5 — 21,001 Total investments with a maturity of one year or less 50,993 26 — 51,019 U.S treasury bills 3,008 — — 3,008 U.S agency securities 176,350 38 — 176,388 Total investments with a maturity of one to two years 179,358 38 — 179,396 Total investments $ 230,351 $ 64 $ — $ 230,415 December 31, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Investments: U.S treasury bills $ 232,336 $ 268 $ — $ 232,604 U.S agency securities 81,201 57 — 81,258 Total investments with a maturity of one year or less $ 313,537 $ 325 $ — $ 313,862

Collaboration and License Arran

Collaboration and License Arrangement with Genentech	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration and License Arrangement with Genentech	5. Collaboration and License Arrangement with Genentech On December 11, 2020, the Company entered into the Genentech Agreement, which granted Genentech a license to develop and commercialize RLY-1971. RLY-1971 is currently being developed in a Phase 1a clinical trial for patients with advanced solid tumors (the “Phase 1a Trial”). Unless Genentech elects to exercise its option to conduct the remainder of the ongoing Phase 1a Trial, the Company is responsible for the completion of this trial. Genentech is responsible for conducting all subsequent clinical development of RLY-1971. The Company is also responsible for the one-time transfer of the active pharmaceutical ingredient (“API”) and other materials related to RLY-1971 to Genentech. Under the Genentech Agreement, the Company is entitled to a non-refundable upfront payment of $75,000, which is due upon completion of certain technology transfer activities and is reflected as accounts receivable on the consolidated balance sheet at December 31, 2020. The Company collected this amount in full in January 2021. The Company is eligible to receive up to $25,000 in near-term milestone payments. The Company is also eligible to receive up to an aggregate of an additional $695,000 upon the achievement of specified development, commercialization and sales-based milestones for RLY-1971 worldwide as well as tiered royalties ranging from low-to-mid teens on annual worldwide net sales of RLY-1971, on a country-by-country basis, subject to reduction in certain circumstances. The Company has the option, exercisable one time at the Company’s sole discretion, to (a) fund half of the development costs of RLY-1971 in the U.S., (b) share half of the net profits or net loss of commercializing RLY-1971 in the U.S. (the “Profit/Cost Share”) and (c) be eligible to receive up to an aggregate of an additional $410,000 upon the achievement of specified commercialization and sales-based milestones for RLY-1971 outside of the U.S and tiered royalties ranging from low-to-mid teens on annual net sales of RLY-1971 outside of the U.S., on a country-by-country basis, subject to reduction in certain circumstances. The Company may elect to opt-out of further participation in the Profit/Cost Share at any time prior to the third anniversary of the first commercial sale of RLY-1971 in the U.S, in which case the financial terms would revert to the terms applicable as if Company had not opted into the Profit/Cost Share as of the effective opt-out date. Genentech may terminate the Genentech Agreement for convenience and the Company may terminate the Genentech Agreement under certain limited circumstances. Unless otherwise terminated, the Genentech Agreement will remain in effect until the expiration of all Genentech’s royalty payment obligations to the Company. Accounting Analysis Identification of the Contract The Company concluded that Genentech is a customer in this arrangement and as such, the arrangement falls within the scope of the revenue recognition guidance in ASC 606. Identification of Performance Obligations At the commencement of the Genentech Agreement, the Company identified the following performance obligations in the agreement: • License to develop and commercialize RLY-1971 and the related know-how; • Research and development services to complete the Phase 1a Trial for RLY-1971; and • Transfer of API and other materials related to RLY-1971 The Company determined that the performance obligations outlined above are both capable of being distinct and distinct within the context of the contract given such rights and activities are independent of each other. The license can be used by Genentech without the research and development services or API outlined above, Determination of Transaction Price The Company determined the transaction price for the Genentech Agreement to be $85,867, which includes both fixed and variable consideration amounts. The total transaction price of $85,867 is comprised of (i) the $75,000 fixed, non-refundable upfront payment, (ii) a $5,000 non-refundable milestone payment due upon the transfer of the Investigational New Drug (“IND”) application Allocation of Transaction Price to Performance Obligations The Company allocated the transaction price of $85,867 based on the stand-alone selling prices (“SSP”) of each of the performance obligations as follows: • $82,654 million for the transfer of the license • $2,896 million for research and development services; and • $317 million for the transfer of API. The SSP for the license was determined using an approach that considered discounted, probability-weighted cash flows related to the license transferred. The Company also reviewed comparable market transactions in determining the SSP of the license. The SSP for the research and development services as well as the transfer of API were based on estimates of the associated effort and cost of these services and cost to manufacture API, adjusted for a reasonable profit margin that would be expected to be realized under similar contracts. The Company performed sensitivity analyses supporting reasonable changes to the SSPs noting no material impact on revenue recognized for the year ended December 31, 2020. Recognition of Revenue The Company is recognizing revenue for each of the three performance obligations as follows: • The Company recognized revenue related to the license at a point in time upon transfer of the license to Genentech. The Company recognized the full amount allocated to the license and related know-how in the fourth quarter of 2020 because the Company had transferred the license upon execution of the Genentech Agreement. Revenue recognized during the year ended December 31, 2020 related to the license amounted to $82,654. • The Company will satisfy the research and development performance obligation for RLY-1971 as the research and development services are performed. The research and development services performance obligation consists of the Company completing the Phase 1a clinical trial initiated in the first quarter of 2020. The Company recognizes revenue related to the research and development services over time using a cost-based input method by calculating actual costs incurred to date at each period end relative to total estimated costs expected to be incurred to fulfill the performance obligation. There was no revenue recognized related to this performance obligation during the year ended December 31, 2020 as the services performed from contract inception to December 31, 2020 were immaterial. • The Company will recognize revenue related to the transfer of API at a point in time upon transfer to Genentech. There was no revenue recognized related to this performance obligation during the year ended December 31, 2020. During the year ended December 31, 2020, the Company recognized an aggregate of $82,654 of revenue from the Genentech Agreement related entirely to the transfer of the license. At December 31, 2020, the Company recorded accounts receivable under the Genentech Agreement in the amount of $75,000 and a contract asset in the amount of $7,654, which is classified as a current asset, on the balance sheet. The contract asset relates to the amount of revenue recognized for which the right to payment is contingent upon conditions other than the passage of time, such as the completion of future milestone activities.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property and Equipment, Net	6. Property and Equipment, Net Property and equipment, net consisted of the following: December 31, 2020 2019 Property and equipment: Laboratory equipment $ 13,534 $ 12,003 Leasehold improvements 886 860 Computer equipment 888 827 Furniture and fixtures 895 895 Construction in process 577 490 16,780 15,075 Less: accumulated depreciation (10,530 ) (6,981 ) Total property and equipment, net $ 6,250 $ 8,094 The Company recorded $3,549 and $2,845 of depreciation expense for the years ended December 31, 2020 and 2019, respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	7. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: December 31, 2020 2019 External research and development $ 5,099 $ 3,077 Professional services 464 336 Other 197 333 Total accrued expenses and other current liabilities $ 5,760 $ 3,746

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2020
Temporary Equity Disclosure [Abstract]
Convertible Preferred Stock	8. Convertible Preferred Stock The Company issued Series A, Series B and Series C convertible preferred stock (collectively, “Convertible Preferred Stock”). Upon issuance of each class of Convertible Preferred Stock, the Company assessed the embedded conversion and liquidity features of the shares and determined that such features did not require the Company to separately account for these features. The Company also concluded that no beneficial conversion feature existed on the issuance date of each class of Convertible Preferred Stock. The Company’s Convertible Preferred Stock was classified outside of stockholders’ equity (deficit) on the consolidated balance sheet prior to the Company’s IPO because the holders of such shares had liquidation rights in the event of a deemed liquidation that, in certain situations, were not solely within the control of the Company and would require the redemption of the then-outstanding Convertible Preferred Stock. The Convertible Preferred Stock was not currently redeemable. Because the occurrence of a deemed liquidation event was not probable, the carrying values of the Convertible Preferred Stock were not accreted to their redemption values. On July 8, 2020, the Company’s board of directors and its Series C preferred stockholders approved a reduction in the conversion price of the Series C preferred stock from $3.21 to $3.027603 and the Series C preferred stockholders relinquished their protective right with respect to the approval of an automatic conversion of preferred stock in a firm commitment underwritten public offering if the per share price is less than $22.80. As a result of the change in the conversion price, the outstanding shares of Series C preferred stock were convertible into 37,206,604 shares of common stock. The changes to the conversion feature were considered to be a significant change to the substantive contractual terms of the Series C preferred stock and, therefore, the Company accounted for the changes as an extinguishment and reissuance of the Series C preferred stock, which required the difference between the fair value of the modified Series C preferred stock and its carrying amount to be treated in a manner similar to the treatment of dividends paid on preferred stock. Upon the closing of the Company’s IPO in July 2020, all outstanding Convertible Preferred Stock automatically converted into 61,992,534 shares of common stock. No Convertible Preferred Stock was outstanding as of December 31, 2020. Prior to January 1, 2019, the Company issued a total of 56,824,740 shares of Series A convertible preferred stock (“Series A preferred stock”), 31,188,115 shares of Series B convertible preferred stock (“Series B preferred stock”) and 122,850,909 shares of Series C convertible preferred stock (“Series C preferred stock”) in exchange for net proceeds of $56,692, $62,876 and $393,587, respectively. During the year ended December 31, 2019, the Company issued an additional 1,779,093 shares of Series C preferred stock at a per share price of $3.21 for proceeds of $5,661, net of issuance costs. Convertible Preferred Stock consisted of the following: December 31, 2019 Preferred Shares Authorized Preferred Shares Issued and Outstanding Carrying Value Liquidation Preference Common Stock Issuable Upon Conversion Series A preferred stock 56,824,740 56,824,740 $ 75,657 $ 56,825 16,002,820 Series B preferred stock 31,188,115 31,188,115 62,876 63,000 8,783,102 Series C preferred stock 249,260,004 124,630,002 399,248 400,000 35,097,955 Total convertible preferred stock 337,272,859 212,642,857 $ 537,781 $ 519,825 59,883,877 There were no shares of Convertible Preferred Stock outstanding at December 31, 2020. The holders of the Convertible Preferred Stock had the following rights and preferences: Voting The holders of the Convertible Preferred Stock had voting rights equivalent to the number of shares of common stock into which their shares of preferred stock would convert. So long as any of the Convertible Preferred Stock was outstanding, a requisite vote of the Convertible Preferred Stockholders, which was defined as a majority of the Convertible Preferred Stockholders, was required to affirm certain corporate actions, which included, but was not limited to, the disposal of assets, the acquisition of assets or a business and the authorization of additional shares of the Company’s capital. In addition, such actions required a requisite vote of the Series C preferred stockholders and a majority vote of the Series B preferred stockholders, if any of the respective preferred stock was outstanding. Dividends The holders of the Convertible Preferred Stock were entitled to receive noncumulative dividends when and if declared by the Company’s board of directors. If the Company declared, paid or set aside, on the same date, a dividend on shares of more than one class or series of capital stock of the Company, the holders of the Convertible Preferred Stock were entitled to the same dividend based on the number of common shares the Convertible Preferred Stock would convert into. No dividends were declared or paid during the years ended December 31, 2020 or 2019. Liquidation Rights In the event of any voluntary or involuntary liquidation, dissolution or winding up of the corporation, holders of the Series C preferred stock then outstanding were entitled to be paid out of the assets of the Company available for distribution to its stockholders before any payment was made to the holders of Series A and B preferred stock or common stock by reason of their ownership thereof, an amount per share equal to the greater of (i) the Series C preferred stock original issue price ($3.21), plus any accrued but unpaid dividends declared, and (ii) an amount per share if the Series C preferred stock had been converted prior to the liquidation event. Next, the holders of the Series A preferred stock then outstanding together with holders of Series B preferred stock were entitled to be paid out of the assets of the Company available for distribution to its stockholders before any payment would be made to the common stockholders by reason of their ownership thereof, an amount per share equal to the greater of (i) their original issue price, which was $1.00 and $2.02 for Series A and B preferred stock, respectively, plus any accrued but unpaid dividends declared, and (ii) an amount per share if the Series A and B preferred stock, respectively, had been converted prior to the liquidation event. Conversion The Convertible Preferred Stock was convertible into common stock at any time at the option of the holder, and was subject to automatic conversion upon the closing of a firm commitment underwritten public offering with either a price per share of at least $22.80 and proceeds of at least $100,000 or approval by a specified vote of the Convertible Preferred Stockholders. As of December 31, 2019, the Convertible Preferred Stock was convertible into 59,382,845 shares of common stock. On July 8, 2020, the required Convertible Preferred Stockholders authorized the automatic conversion of all shares of Convertible Preferred Stock in an IPO, regardless of the price per share or total proceeds raised, as long as the IPO was completed on or before September 30, 2020. Protective Rights For as long as any of the Series C preferred stock was outstanding, a requisite vote of the Convertible Preferred Stockholders was required to affirm a liquidation, dissolution, a merger or consolidation or any other deemed liquidation event if the per share proceeds to the holders of the Series C preferred stock would be equal to or greater than $22.80 per share. In addition, both a requisite vote of the Convertible Preferred Stockholders and a majority of the Series C preferred stockholders was required to affirm a liquidation, dissolution, a merger or consolidation or any other deemed liquidation event if the per share proceeds to the holders of the Series C preferred stock was less than $22.80 per share.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2020
Stockholders Equity Note [Abstract]
Common Stock	9. Common Stock Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends, as may be declared by the Company’s board of directors, however, holders of convertible preferred stock were entitled to any dividend received by the common stockholders if each preferred share had been converted into common stock. As of December 31, 2020 and 2019, no dividends had been declared. The Company issued restricted shares of common stock to its founders and non-employees. In addition, the Company issued restricted shares of common stock upon the early exercise of stock options under the Company’s 2016 Stock Option and Grant Plan (the “2016 Stock Plan”). The restrictions on the common shares generally lapse over four years. The Company included the proceeds from the sale of the restricted shares of common stock as a restricted stock liability on the accompanying consolidated balance sheets. Amounts are reclassified to additional paid-in capital as the restrictions lapse. The Company has the right to repurchase any unvested shares of restricted common stock at the original cost in the event of termination. The following table summarizes the restricted stock activity for the year ended December 31, 2020: Shares Weighted- Average Purchase Price Unvested at December 31, 2019 679,158 $ 0.21 Vested (579,825 ) 0.26 Cancelled (14,844 ) 0.03 Unvested at December 31, 2020 84,489 0.04 The fair value of shares that vested during the year ended December 31, 2020 was $9,619. The Company has reserved the following shares of common stock: December 31, 2020 2019 Conversion of Series A preferred stock — 16,002,820 Conversion of Series B preferred stock — 8,783,102 Conversion of Series C preferred stock — 35,097,955 Shares reserved under the compensation plan 8,026,772 8,407,169 Total shares of common stock reserved for issuance 8,026,772 68,291,046 Employee Stock Purchase Plan On July 8, 2020, the Company’s stockholders approved the 2020 Employee Stock Purchase Plan (the “ESPP”). The ESPP became effective on the date immediately prior to the effectiveness of Company’s registration statement on Form S-1 for its IPO. As of December 31, 2020, the ESPP provides for the issuance of up to 1,092,532 of share-based awards. As of December 31, 2020, no shares have been issued under the ESPP.

Share-Based Payments

Share-Based Payments	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-Based Payments	10. Share-Based Payments In 2016, the Company adopted the 2016 Stock Plan. On July 8, 2020, the Company’s stockholders approved the 2020 Stock Option and Incentive Plan (the “2020 Stock Plan”), which became effective on the date immediately prior to the effectiveness of the Company’s registration statement on Form S-1 for its IPO. The 2020 Stock Plan provides for the issuance of up to 8,376,080 of share-based awards. Subsequent to July 20, 2020, no further awards will be made under the 2016 Stock Plan and all future equity-based awards will be granted under the 2020 Stock Plan. To the extent outstanding options granted under the 2016 Plan are cancelled, forfeited or otherwise terminated without being exercised and would otherwise have been returned to the share reserve under the 2016 Plan, the number of shares underlying such awards will be available for future grant under the 2020 Stock Plan. All of the Company’s employees, officers, directors and consultants are eligible to be granted options, restricted stock units and other stock-based awards under the terms of the 2020 Stock Plan. There were 8,026,772 share-based awards available for grant at December 31, 2020. The following table summarizes the stock option activity under the 2016 Stock Plan and the 2020 Stock Plan for the year ended December 31, 2020: Number of Stock Options Weighted- Average Exercise Price Weighted- Average Remaining Term (years) Aggregate Intrinsic Value Outstanding at December 31, 2019 5,306,176 $ 4.62 8.99 $ 3,214 Granted 2,898,663 10.90 Exercised (297,000 ) 4.09 Cancelled (210,781 ) 4.91 Outstanding at December 31, 2020 7,697,058 $ 6.99 8.50 $ 266,050 Vested at December 31, 2020 2,148,119 $ 4.49 7.90 $ 79,625 Non-vested at December 31, 2020 5,548,939 $ 7.96 8.74 $ 186,425 In the first quarter of 2020, the Company’s board of directors approved the issuance of options with performance-based vesting conditions to purchase 1,960,547 shares of common stock. The commencement of vesting was based on the achievement of certain scientific and operational milestones during a two-year period, for which the achievement was discretionary and subject to the approval of the Company’s board of directors. Accordingly, the Company applied variable accounting for these awards until the board of directors approved the commencement of vesting for the options. The service inception date preceded the grant date for these awards as the awards were authorized prior to the grant date, the recipients were providing service prior to the grant date and there were performance conditions that, if not met by the accounting grant date, would have resulted in the forfeiture of the award. The stock-based compensation expense for the options was determined based on the fair value of the awards on the accounting grant date. The Company’s board of directors, in its discretion, determined that a portion of the performance conditions were achieved during the second quarter of 2020 and that the remaining portion of the performance conditions were achieved during the fourth quarter of 2020. The grant dates for all performance-based awards was therefore known as of December 31, 2020, and all performance conditions have been resolved. The Company recognized stock-based compensation expense associated with the awards with performance-based vesting conditions in the amount of $25,527 in the statement of operations for the year ended December 31, 2020. Expense for these awards is recognized using an accelerated attribution model, over the four-year vesting term, commencing upon grant date. The Company estimated the fair value of its stock options using the following assumptions: Year Ended December 31, 2020 2019 Risk-free interest rate 0.4 - 1.8% 1.5 – 2.5% Expected term (in years) 6.3 6.3 Expected volatility 73.5 - 77.6% 72.8 – 73.47% Expected dividend yield 0 % 0 % The weighted average grant date fair value of stock options granted during the years ended December 31, 2020 and 2019 was $30.14 per share and $3.34 per share, respectively. Stock-based compensation expense included in the Company’s consolidated statements of operations and comprehensive loss is as follows: Year Ended December 31, 2020 2019 Research and development expenses $ 14,691 $ 2,687 General and administrative expenses 17,269 1,769 $ 31,960 $ 4,456 As of December 31, 2020, total unrecognized compensation cost related to the unvested stock-based awards was $69,948, which is expected to be recognized over a weighted average period of 2.61 years.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes During the years ended December 31, 2020 and 2019, the Company recorded no income tax benefits due to the losses incurred due to the uncertainty of future taxable income. A reconciliation of the expected income tax (benefit) computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows for the year ended December 31, 2020 and 2019: December 31, 2020 2019 Income tax computed at federal statutory rate 21 % 21.0 % State taxes, net of federal benefit 5.7 % 7.0 % Change in valuation allowance (27.3 )% (31.0 )% R&D credit carryovers 7.6 % 4.1 % Stock-based compensation (6.7 )% (0.9 )% Permanent differences (0.3 )% (0.2 )% Total 0.0 % 0.0 % The Company’s deferred tax assets at December 31, 2020 and 2019, consist of the following: December 31, 2020 2019 Deferred tax assets: Net operating losses $ 48,832 $ 42,647 Tax credit carryforwards 10,270 6,309 Lease liability 6,430 6,542 Intangibles 1,469 1,498 Stock-based compensation 4,496 534 Depreciation and amortization 230 188 Other 14 13 Total gross deferred tax asset 71,741 57,731 Valuation allowance (65,813 ) (51,537 ) Net deferred tax asset 5,928 6,194 Deferred tax liability Operating lease assets (5,928 ) (6,194 ) Total deferred tax liability (5,928 ) (6,194 ) $ — $ — The Company has incurred net operating losses (“NOL”) since inception. As of December 31, 2020, the Company had federal NOL carryforwards of $174,028 available to reduce taxable income, of which $43,127 expire beginning in 2035 and $130,901 do not expire. The Company has state NOL carryforwards of $192,346 as of December 31, 2020 available to reduce future state taxable income, which expire at various dates beginning in 2035. As of December 31, 2020, the Company also had available federal research and development tax credit carryforwards of $8,139 available to reduce future tax liabilities, which begin to expire beginning in 2035. The Company also has state research and development tax credit carryforwards of $2,699 available to reduce future state tax liabilities, which expire at various dates beginning in 2030. Utilization of the NOL carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 (“Section 382”) due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position. The Company recorded a valuation allowance against its deferred tax assets for the years ended December 31, 2020 and 2019 because the Company’s management believes that it is more likely than not that these assets will not be realized. The valuation allowance increased by approximately $14,276 and $23,307 for the years ended December 31, 2020 and 2019, respectively, primarily as a result of operating losses generated with no corresponding financial statement benefit. The Company had no unrecognized tax benefits as of December 31, 2020 and 2019. The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending tax examinations. The Company’s tax years are still open under statute from inception to the present. In response to the COVID-19 pandemic, the Coronavirus Aid, Relief and Economic Security Act (CARES Act) was signed into law in March 2020. The CARES Act lifts certain deduction limitations originally imposed by the Tax Cuts and Jobs Act of 2017 (“2017 Tax Act”). Corporate taxpayers may carryback NOLs originating during 2018 through 2020 for up to five years, which was not previously allowed under the 2017 Tax Act. The CARES Act also eliminates the 80% of taxable income limitations by allowing corporate entities to fully utilize NOL carryforwards to offset taxable income in 2018, 2019 or 2020. Taxpayers may generally deduct interest up to the sum of 50% of adjusted taxable income plus business interest income (30% limit under the 2017 Tax Act) for tax years beginning January 1, 2019 and 2020. The CARES Act allows taxpayers with alternative minimum tax credits to claim a refund in 2020 for the entire amount of the credits instead of recovering the credits through refunds over a period of years, as originally enacted by the 2017 Tax Act. In addition, the CARES Act raises the corporate charitable deduction limit to 25% of taxable income and makes qualified improvement property generally eligible for 15-year cost-recovery and 100% bonus depreciation. The enactment of the CARES Act did not result in any adjustments to the Company’s income tax provision for the year ended December 31, 2020, or to the Company’s net deferred tax assets as of December 31, 2020, since the Company has not recorded any U.S. federal or state income tax benefits for the net losses incurred in any year due to the uncertainty of realizing a benefit from those items.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	12. Net Loss Per Share The following table summarizes the computation of basic and diluted net loss per share of the Company: Year Ended December 31, 2020 2019 Net loss $ (52,412 ) $ (75,305 ) Deemed dividend resulting from extinguishment upon modification of Series C preferred stock (177,789 ) — Net loss attributable to common stockholders $ (230,201 ) $ (75,305 ) Net loss attributable to common stockholders per share, basic and diluted $ (5.40 ) $ (21.82 ) Weighted average shares of common stock, basic and diluted 42,619,582 3,450,500 As discussed in Note 8, on July 8, 2020, the Company’s board of directors and its Series C preferred stockholders approved an amendment to the conversion preferences and rights of the Series C preferred stock which, among other changes, resulted in a reduction in the conversion price of the Series C preferred stock from $3.21 to $3.027603. The changes to the conversion feature were considered to be a significant change to the substantive contractual terms of the Series C preferred stock and, therefore, the Company accounted for the changes as an extinguishment and reissuance of the Series C preferred stock. In accordance with SEC staff guidance codified in ASC 260-10-S99-2, when equity classified preferred shares are extinguished, the difference between (1) the fair value of the consideration transferred to the holders of the preferred shares and (2) the carrying amount of the preferred shares, net of issuance costs, is subtracted from (or added back to) net income to arrive at income available to common stockholders in the calculation of earnings per share. This difference between the fair value of consideration transferred and carrying amount of the preferred shares, also referred to as a “deemed dividend”, was therefore added back to net loss above to derive net loss attributable to common stockholders. The Company’s potentially dilutive securities, which include Convertible Preferred Stock (prior to the IPO), options to purchase common stock and unvested restricted stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: Year Ended December 31, 2020 2019 Convertible preferred stock — 59,883,877 Options to purchase common stock 7,697,058 5,306,176 Unvested restricted stock 84,489 679,158 7,781,547 65,869,211

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments and Contingencies Intellectual Property License The Company has a Collaboration and License Agreement with D. E. Shaw Research, LLC (“D. E. Shaw Research”), which held 9,999,999 shares of Series A preferred stock and 1,557,875 shares of Series C preferred stock at December 31, 2019. Upon the IPO these shares were converted into 3,281,253 shares of common stock, which are outstanding at December 31, 2020. The agreement provides that the parties will jointly conduct research efforts with the goal of identifying and developing product candidates. The original term of the agreement was three years and required the Company to pay an annual fee of $1,000. On June 15, 2020, the Company and D. E. Shaw Research agreed to amend the Collaboration and License Agreement (the “Amended and Restated Collaboration and License Agreement”). The Amended and Restated Collaboration and License Agreement extended the term of the agreement to August 16, 2025 and increased the annual fee from $1,000 to $7,900. The Amended and Restated Collaboration and License Agreement automatically renews for successive one year periods unless either party provides at least one year notice of non-renewal, and the annual fee during each of the one year renewal terms is subject to the mutual agreement of the Company and D. E. Shaw Research. The Company is obligated to pay potential development milestone payments under the terms of the agreement up to $7,300 per target, plus sales milestones and royalties, upon the achievement of certain specified contingent events. Such payments for achievement of development and regulatory milestones total up to $7,250 in the aggregate for each of the first three products the Company develops, and up to $6,250 in the aggregate for each product the Company develops after the first three. The Company assessed the milestone and royalty events through December 31, 2020 and concluded $1,500 was due to D.E. Shaw related to the execution of the Genentech Agreement in December 2020. The Company concluded no such payments were due as of December 31, 2019. The Company recorded research and development expense of $6,376 and $1,500 under this agreement for the years ended December 31, 2020 and 2019, respectively. At December 31, 2020 and December 31, 2019, the Company had an accrued expense balance to D. E. Shaw Research of approximately $1,500 and $372, respectively, on its balance sheets. Other Research Arrangements The Company has certain other research and license arrangements with third-parties, which provide the Company with research services with the goal of identifying and developing product candidates. The Company is obligated to pay development milestone payments for up to four targets, each in the range of $4,000 to $7,000 upon the achievement of certain specified contingent events. The Company assessed the milestones at December 31, 2020 and 2019 and concluded no such milestone payments were due. The Company incurred approximately $2,704 and $3,493 of research and development expense under these agreements in the years ended December 31, 2020 and 2019, respectively.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	14. Leases 215 First Street The Company leased office and laboratory space at 215 First Street in Cambridge, Massachusetts (“First Lease”) under an operating lease, which commenced in November 2015 and was originally set to expire in December 2020. As discussed below, the Company executed a lease at 399 Binney Street (“Binney Lease”) whereby the Company vacated the 215 First Street lease in January 2019 and the future lease commitments terminated at no cost once the Binney Lease commenced. The lease included certain tenant improvement allowances, which the Company amortized through January 2019, the termination of the lease. 399 Binney Street In December 2017, the Company entered into a facility lease agreement for approximately 44,336 square feet of office and laboratory space at 399 Binney Street, Cambridge, Massachusetts, which was increased to 44,807 square feet in January 2018. The Company gained control of the leased space in January 2019 and recorded a right of use asset and a lease liability, accordingly. The lease expires in April 2029, subject to certain renewal options, which have not been included in the Company’s right of use asset and liability, as the Company is not reasonably certain to exercise those options. In September 2020, the Company entered into an amendment to its facility lease agreement to expand the leased area by approximately 1,824 square feet of office space at 399 Binney Street, Cambridge, Massachusetts. The amended lease expires in April 2029, subject to certain renewal options. The amendment to the lease agreement met the criteria to be accounted for as a separate lease. The Company gained control of the leased space in October 2020 and recorded a right of use asset and a lease liability, accordingly. The right of use asset and lease liability recorded in connection with this amendment were not material. As discussed in Note 2, the Company provided a letter of credit in the amount of $878 with a financial institution, which expires September 30, 2028. The following table summarizes the presentation of the Company’s operating leases on its consolidated balance sheets: December 31, December 31, Balance sheet location 2020 2019 Assets: Operating lease assets Operating lease assets $ 22,579 $ 23,560 Liabilities: Current operating lease liabilities Operating lease liabilities $ 1,521 $ 1,249 Non-current operating lease liabilities Operating lease liabilities, net of current portion 22,901 23,583 Total lease liabilities $ 24,422 $ 24,832 The following table summarizes the effect of lease costs in the Company’s consolidated statements of operations and comprehensive loss for the years ended December 31, 2020 and 2019: Statement of operations location Year Ended December 31, 2020 Year Ended December 31, 2019 Operating lease costs Research and development $ 3,273 $ 3,216 General and administrative 748 581 Total operating lease cost $ 4,021 $ 3,797 The Company made cash payments of $4,878 and $2,602 under the lease agreements during the years ended December 31, 2020 and 2019, respectively. The minimum lease payments as of December 31, 2020 for the next five years and thereafter is expected to be as follows: Year Ending December 31, Amount 2021 $ 3,985 2022 4,134 2023 4,254 2024 4,377 2025 4,503 Thereafter 15,959 Total lease payments 37,212 Less: interest (12,790 ) Present value of operating lease liabilities $ 24,422 The weighted average remaining lease term and weighted average discount rate of the operating leases were 8.3 years and 10.4%, respectively, at December 31, 2020. The weighted average remaining lease term and weighted average discount rate of the operating leases were 9.3 years and 10.4%, respectively, at December 31, 2019.

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2020
Postemployment Benefits [Abstract]
Retirement Benefits	15. Employee Benefits In 2016, the Company established a defined-contribution plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. The Company made matching contributions to the 401(k) Plan of $590 for the year ended December 31, 2020. The Company was not required to make and did not make any matching contributions to the 401(k) Plan for the year ended December 31, 2019.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	16. Related Party Transactions From inception to December 31, 2020, the Company received consulting and management services from Third Rock Ventures LLP (“TRV”), an entity affiliated with certain of the Company’s investors. The Company did not incur expenses for such services during the year ended December 31, 2020 .

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	17. Subsequent Events In preparing the consolidated financial statements as of December 31, 2020, the Company evaluated subsequent events for recognition and measurement purposes through the filing date of this Annual Report on Form 10-K. The Company concluded that no events or transactions have occurred that require disclosure in the accompanying consolidated financial statements.

Significant Accounting Policies

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) for reporting on Form 10-K. The Company’s consolidated financial statements include the accounts of Relay Therapeutics, Inc. and its wholly-owned subsidiary, Relay Therapeutics Securities Corporation. All intercompany balances and transactions have been eliminated.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development and manufacturing expenses, the valuation of equity instruments, the determination of the transaction price and standalone selling price of performance obligations under Accounting Standards Codification Topic 606, Revenue from Contracts with Customers The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses, clinical trials and research and development costs, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain or treat COVID-19, as well as the economic impact on local, regional, national and international markets. The Company has made estimates of the impact of COVID-19 within its financial statements and there may be changes to those estimates in future periods. Actual results could differ from the Company’s estimates.
Segment Information	Segment Information The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on using innovative experimental and computational approaches on protein motion for making medicines against intractable precision medicine targets. The Company operates in the United States and all tangible assets are held in the United States.
Cash Equivalents	Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market funds, are stated at fair value.
Restricted Cash	Restricted Cash The Company had restricted cash of $878 as of December 31, 2020 and 2019 to secure a letter of credit in connection with the lease of the Company’s facilities (see Note 14). The Company classified the restricted cash as a noncurrent asset on its consolidated balance sheets.
Investments	Investments Investments in marketable securities are classified as available-for-sale. Available-for-sale securities are measured and reported at fair value using quoted prices in active markets for similar securities. Unrealized gains and losses on available-for-sale securities are reported as a separate component of stockholders’ equity (deficit). Premiums or discounts from par value are amortized to investment income over the life of the underlying investment. All of the Company’s available-for-sale securities are available to the Company for use in current operations. As a result, the Company classified all of these securities as current assets even though the stated maturity of some individual securities may be one year or more beyond the balance sheet date. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the consolidated statements of operations and comprehensive loss. If any adjustment is required to reflect a decline in the value of the investment that the Company considers to be “other than temporary”, the Company recognizes a charge to the consolidated statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.
Concentration of Credit Risk and Significant Suppliers	Concentration of Credit Risk and Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. From time to time, the Company has maintained all of its cash, cash equivalents and investments at certain accredited financial institutions in amounts that exceed federally insured limits. The Company generally invests its excess capital in money market funds, U.S. treasury bonds, U.S. treasury bills and agency bonds are subject to minimal credit and market risk. Management has established guidelines relative to credit ratings and maturities intended to safeguard principal balances and maintain liquidity. The investment portfolio is maintained in accordance with the Company’s investment policy, which defines allowable investments, specifies credit quality standards and limits the credit exposure of any single issuer. The Company is dependent on third-party suppliers for research and development activities of its programs, including preclinical and clinical testing. In particular, the Company relies and expects to continue to rely on a small number of these suppliers, including D. E. Shaw Research, LLC as discussed in Note 13, to meet its requirements for its programs. These programs could be adversely affected by a significant interruption in pre-clinical and clinical testing and the supply of active pharmaceutical ingredients and formulated drugs.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.
Revenue Recognition	Revenue Recognition The Company accounts for revenue recognition in accordance with Accounting Standards Codification Topic (“ASC”) 606, Revenue from Contracts with Customers At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within the contract and determines those that are performance obligations. The Company then determines the transaction price and allocates it to the performance obligations using the relative selling price model. As part of the accounting for these arrangements, the Company must use significant judgment to determine: (a) the number of performance obligations based on the determination under step (ii) above; (b) the transaction price under step (iii) above, including the determination of whether milestones or other variable consideration should be included in the transaction price; and (c) the stand-alone selling price for each performance obligation identified in the contract for the allocation of the transaction price in step (iv) above. The Company utilizes key assumptions and judgments to determine the stand-alone selling price for each performance obligation, which may include discounted cash flow models, evaluation of comparable transactions, pricing considered in negotiating the transaction and estimated costs, to determine how the transaction price is allocated among the performance obligations Once the performance obligations are identified, the transaction price is allocated to each performance obligation based on the relative stand-alone selling price. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied, either at a point in time or over time. If the performance obligation is satisfied over time, the Company recognizes revenue based on the use of either an output or input method. As of December 31, 2020, the Company had one collaboration and license agreement with Genentech, which the Company entered into on December 11, 2020. For a discussion of the accounting related to the Genentech Agreement, see Note 5, Collaboration and License Arrangement with Genentech
Lease Agreements	Lease Agreements Under ASC 842, Leases Right-of-use assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an estimate of its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. Operating lease right-of-use assets also include the effect of any lease payments made prior to commencement and excludes lease incentives. The lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which are accounted for as a combined element.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the useful life of the asset. Laboratory and computer equipment are depreciated over three years. Furniture and fixtures are depreciated over five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the related asset. Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company continually evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured in an amount by which the book values of the assets exceed their fair value. The Company did not recognize any impairment losses for the years ended December 31, 2020 and 2019.
Classification and Accretion of Convertible Preferred Stock	Classification and Accretion of Convertible Preferred Stock The Company’s convertible preferred stock was classified outside of stockholders’ equity (deficit) on the consolidated balance sheet because the holders of such shares had liquidation rights in the event of a deemed liquidation that, in certain situations, were not solely within the control of the Company and would require the redemption of the then-outstanding convertible preferred stock. The convertible preferred stock was not currently redeemable, except in the event of a deemed liquidation (see Note 8). Because the occurrence of a deemed liquidation event was not probable, the carrying value of the convertible preferred stock was not accreted to their redemption values. Subsequent adjustments to the carrying values of the convertible preferred stock would have been made only when a deemed liquidation event became probable. Upon the closing of the Company’s IPO in July 2020, all outstanding convertible preferred stock automatically converted into 61,992,534 shares of common stock.
Stock-Based Compensation	Stock-Based Compensation The Company measures stock options and other stock-based awards granted to employees, directors and non-employees based on their fair value on the date of grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award. The Company recognizes the impact of forfeitures on stock-based compensation expense as forfeitures occur. The Company issued certain options with performance-based vesting conditions whereby the service inception date preceded the accounting grant date and therefore applied variable accounting for the awards until the fair value of the awards was known on the accounting grant date. The board of directors approved the commencement of vesting for all such awards in 2020, therefore the Company no longer applies variable accounting as of December 11, 2020. The Company estimates the fair value of each stock option grant on the date of grant using the Black-Scholes option-pricing model, which uses as inputs the fair value of the Company’s common stock and assumptions the Company makes for the volatility of its common stock, the expected term of the stock options, the risk-free interest rate for a period that approximates the expected term of the stock options and the expected dividend yield. Prior to the Company’s IPO, the estimated fair value of its common stock was determined by the board of directors, or compensation committee thereof, as of the date of each option grant, with input from management, considering the most recently available third-party valuations of common stock and the board of directors’ assessment of additional objective and subjective factors that it believed were relevant and which may have changed from the date of the most recent valuation through the date of the grant. Historically, these independent third-party valuations of the Company’s equity instruments were performed contemporaneously with identified value inflection points. These third-party valuations were performed in accordance with the guidance outlined in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation Following the Company’s IPO, in connection with the accounting for granted stock options and other awards the Company may grant, the fair value of the Company’s common stock is determined based on the quoted market price of its common stock.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses include salaries, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including allocated facility-related expenses and external costs of outside vendors engaged to conduct both pre-clinical studies and clinical trials. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made.
Research and Manufacturing Contracts	Research and Manufacturing Contracts The Company has entered into various research and development contracts with research institutions and other companies whose costs are included in research and development expense in the accompanying consolidated statements of operations and comprehensive loss. These agreements are generally cancelable and related payments are recorded as research and development expenses as the underlying services are performed. When evaluating the adequacy of the expense recognized, the Company analyzes progress of the services, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the expense recognized and the related prepaid or accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical estimates have not been materially different from the actual costs.
Patent Costs	Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.
Income Taxes	Income Taxes The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company’s financial statements or tax returns. Under this method, deferred tax assets and liabilities are determined based on differences between the financial statement carrying amounts and the tax bases of the assets and liabilities using the enacted tax rates in effect in the years in which the differences are expected to reverse. A valuation allowance against deferred tax assets is recorded if, based on the weight of the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2020 and 2019, other comprehensive income (loss) consisted of changes in unrealized gains and losses from available-for-sale investments.
Net Loss Per Common Share	Net Loss Per Common Share Basic net loss per share is computed using the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed using the sum of the weighted average number of common shares outstanding during the period and the effect of dilutive securities. The Company applies the two-class method to calculate its basic and diluted net loss per share as the Company has issued shares that meet the definition of participating securities. The two-class method is an earnings allocation formula that treats a participating security as having rights to earnings that otherwise would have been available to common stockholders. The Company’s participating securities contractually entitle the holders of such shares to participate in dividends; but do not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such participating securities. Additionally, in periods in which the Company reports a net loss, diluted net loss per share is the same as basic net loss per share, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. For additional discussion of net loss per common share, please see Note 12, Net Loss Per Share.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements The Company adopted Accounting Standards Update (“ASU”) No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In June 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates In August 2020, the FASB issued ASU No. 2020-06, Debt – Debt with Conversion and Other Options and Derivatives and Hedging—Contracts in Entity’s Own Equity In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that the Company adopts as of the specified effective date. The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected to use the extended transition period related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different effective dates for public and nonpublic companies, the Company can adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and can do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company.

Fair Value of Financial Assets

Fair Value of Financial Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on a Recurring Basis and Level of the Fair Value Hierarchy	The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of December 31, 2020: Level 1 Level 2 Level 3 Total Assets Cash equivalents: Money market funds $ 447,146 $ — $ — $ 447,146 Investments: US treasury bills — 33,026 — 33,026 US agency securities — 197,389 — 197,389 Total investments — 230,415 — 230,415 Total $ 447,146 $ 230,415 $ — $ 677,561 Fair Value Measurements as of December 31, 2019: Level 1 Level 2 Level 3 Total Assets Cash equivalents: Money market funds $ 41,658 $ — $ — $ 41,658 Investments: US treasury bills — 232,604 — 232,604 US agency securities — 81,258 — 81,258 Total investments — 313,862 — 313,862 Total $ 41,658 $ 313,862 $ — $ 355,520

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2020
Schedule Of Investments [Abstract]
Summary of Fair Value of Available-for-Sale Investments by Type of Security	The fair value of available-for-sale investments by type of security was as follows: December 31, 2020 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Investments: U.S treasury bills $ 29,997 $ 21 $ — $ 30,018 U.S agency securities 20,996 5 — 21,001 Total investments with a maturity of one year or less 50,993 26 — 51,019 U.S treasury bills 3,008 — — 3,008 U.S agency securities 176,350 38 — 176,388 Total investments with a maturity of one to two years 179,358 38 — 179,396 Total investments $ 230,351 $ 64 $ — $ 230,415 December 31, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Investments: U.S treasury bills $ 232,336 $ 268 $ — $ 232,604 U.S agency securities 81,201 57 — 81,258 Total investments with a maturity of one year or less $ 313,537 $ 325 $ — $ 313,862

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consisted of the following: December 31, 2020 2019 Property and equipment: Laboratory equipment $ 13,534 $ 12,003 Leasehold improvements 886 860 Computer equipment 888 827 Furniture and fixtures 895 895 Construction in process 577 490 16,780 15,075 Less: accumulated depreciation (10,530 ) (6,981 ) Total property and equipment, net $ 6,250 $ 8,094

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: December 31, 2020 2019 External research and development $ 5,099 $ 3,077 Professional services 464 336 Other 197 333 Total accrued expenses and other current liabilities $ 5,760 $ 3,746

Convertible Preferred Stock (Ta

Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2020
Temporary Equity Disclosure [Abstract]
Summary of Convertible Preferred Stock	Convertible Preferred Stock consisted of the following: December 31, 2019 Preferred Shares Authorized Preferred Shares Issued and Outstanding Carrying Value Liquidation Preference Common Stock Issuable Upon Conversion Series A preferred stock 56,824,740 56,824,740 $ 75,657 $ 56,825 16,002,820 Series B preferred stock 31,188,115 31,188,115 62,876 63,000 8,783,102 Series C preferred stock 249,260,004 124,630,002 399,248 400,000 35,097,955 Total convertible preferred stock 337,272,859 212,642,857 $ 537,781 $ 519,825 59,883,877

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2020
Stockholders Equity Note [Abstract]
Summary Of The Restricted Stock Activity	The following table summarizes the restricted stock activity for the year ended December 31, 2020: Shares Weighted- Average Purchase Price Unvested at December 31, 2019 679,158 $ 0.21 Vested (579,825 ) 0.26 Cancelled (14,844 ) 0.03 Unvested at December 31, 2020 84,489 0.04
Summary of Reserved Shares of Common Stock	The Company has reserved the following shares of common stock: December 31, 2020 2019 Conversion of Series A preferred stock — 16,002,820 Conversion of Series B preferred stock — 8,783,102 Conversion of Series C preferred stock — 35,097,955 Shares reserved under the compensation plan 8,026,772 8,407,169 Total shares of common stock reserved for issuance 8,026,772 68,291,046

Share-Based Payments (Tables)

Share-Based Payments (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock Option Activity	The following table summarizes the stock option activity under the 2016 Stock Plan and the 2020 Stock Plan for the year ended December 31, 2020: Number of Stock Options Weighted- Average Exercise Price Weighted- Average Remaining Term (years) Aggregate Intrinsic Value Outstanding at December 31, 2019 5,306,176 $ 4.62 8.99 $ 3,214 Granted 2,898,663 10.90 Exercised (297,000 ) 4.09 Cancelled (210,781 ) 4.91 Outstanding at December 31, 2020 7,697,058 $ 6.99 8.50 $ 266,050 Vested at December 31, 2020 2,148,119 $ 4.49 7.90 $ 79,625 Non-vested at December 31, 2020 5,548,939 $ 7.96 8.74 $ 186,425
Schedule of Estimated Fair Value of Stock Options	The Company estimated the fair value of its stock options using the following assumptions: Year Ended December 31, 2020 2019 Risk-free interest rate 0.4 - 1.8% 1.5 – 2.5% Expected term (in years) 6.3 6.3 Expected volatility 73.5 - 77.6% 72.8 – 73.47% Expected dividend yield 0 % 0 %
Schedule of Stock-Based Compensation Expense Included In The Company's Consolidated Statements of Operations And Comprehensive Loss	Stock-based compensation expense included in the Company’s consolidated statements of operations and comprehensive loss is as follows: Year Ended December 31, 2020 2019 Research and development expenses $ 14,691 $ 2,687 General and administrative expenses 17,269 1,769 $ 31,960 $ 4,456

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Summary of Reconciliation of Expected Income Tax (Benefit) Computed Using Federal Statutory Income Tax Rate to Effective Income Tax Rate	A reconciliation of the expected income tax (benefit) computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows for the year ended December 31, 2020 and 2019: December 31, 2020 2019 Income tax computed at federal statutory rate 21 % 21.0 % State taxes, net of federal benefit 5.7 % 7.0 % Change in valuation allowance (27.3 )% (31.0 )% R&D credit carryovers 7.6 % 4.1 % Stock-based compensation (6.7 )% (0.9 )% Permanent differences (0.3 )% (0.2 )% Total 0.0 % 0.0 %
Summary of Deferred Tax Assets	The Company’s deferred tax assets at December 31, 2020 and 2019, consist of the following: December 31, 2020 2019 Deferred tax assets: Net operating losses $ 48,832 $ 42,647 Tax credit carryforwards 10,270 6,309 Lease liability 6,430 6,542 Intangibles 1,469 1,498 Stock-based compensation 4,496 534 Depreciation and amortization 230 188 Other 14 13 Total gross deferred tax asset 71,741 57,731 Valuation allowance (65,813 ) (51,537 ) Net deferred tax asset 5,928 6,194 Deferred tax liability Operating lease assets (5,928 ) (6,194 ) Total deferred tax liability (5,928 ) (6,194 ) $ — $ —

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Summary of Computation of Basic and Diluted Net Loss Per Share	The following table summarizes the computation of basic and diluted net loss per share of the Company: Year Ended December 31, 2020 2019 Net loss $ (52,412 ) $ (75,305 ) Deemed dividend resulting from extinguishment upon modification of Series C preferred stock (177,789 ) — Net loss attributable to common stockholders $ (230,201 ) $ (75,305 ) Net loss attributable to common stockholders per share, basic and diluted $ (5.40 ) $ (21.82 ) Weighted average shares of common stock, basic and diluted 42,619,582 3,450,500
Summary of Antidilutive Securities Excluded From Computation of Earnings Per Share	The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: Year Ended December 31, 2020 2019 Convertible preferred stock — 59,883,877 Options to purchase common stock 7,697,058 5,306,176 Unvested restricted stock 84,489 679,158 7,781,547 65,869,211

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Schedule of Operating Leases Presentation in Consolidated Balance Sheets	The following table summarizes the presentation of the Company’s operating leases on its consolidated balance sheets: December 31, December 31, Balance sheet location 2020 2019 Assets: Operating lease assets Operating lease assets $ 22,579 $ 23,560 Liabilities: Current operating lease liabilities Operating lease liabilities $ 1,521 $ 1,249 Non-current operating lease liabilities Operating lease liabilities, net of current portion 22,901 23,583 Total lease liabilities $ 24,422 $ 24,832
Summary of Operating Lease Presentation in Consolidated Statements of Operations and Comprehensive Loss	The following table summarizes the effect of lease costs in the Company’s consolidated statements of operations and comprehensive loss for the years ended December 31, 2020 and 2019: Statement of operations location Year Ended December 31, 2020 Year Ended December 31, 2019 Operating lease costs Research and development $ 3,273 $ 3,216 General and administrative 748 581 Total operating lease cost $ 4,021 $ 3,797
Summary of Future Minimum Lease Payments	The minimum lease payments as of December 31, 2020 for the next five years and thereafter is expected to be as follows: Year Ending December 31, Amount 2021 $ 3,985 2022 4,134 2023 4,254 2024 4,377 2025 4,503 Thereafter 15,959 Total lease payments 37,212 Less: interest (12,790 ) Present value of operating lease liabilities $ 24,422

Nature of Business and Basis _2

Nature of Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 20, 2020	Jul. 08, 2020	Jan. 31, 2021	Dec. 31, 2020	Jul. 07, 2020	Dec. 31, 2019
Nature of Business and Basis of Presentation [Line Items]
Accumulated deficit				$ (404,228)		$ (189,482)
Number of shares issued in transaction	23,000,000
Sale price of stock	$ 20
Issuance of common stock in public offering	$ 425,293			425,293
Underwriting discounts and commissions	32,200
Expense on initial public offering	$ 2,507			$ 2,507
Conversion of stock shares converted	61,992,534
Common stock shares authorized		150,000,000		150,000,000	260,000,000	260,000,000
Stockholders' Equity, Reverse Stock Split		one-for-3.55092
Genentech [Member] | Subsequent Event [Member] | Collaboration and License Agreement [Member]
Nature of Business and Basis of Presentation [Line Items]
Upfront payment received			$ 75,000

Significant Accounting Polici_2

Significant Accounting Policies - Additional Information (Detail)	1 Months Ended		12 Months Ended
	Jul. 31, 2020shares	Nov. 30, 2015	Dec. 31, 2020USD ($)SegmentAgreement	Dec. 31, 2019USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments | Segment			1
Maturity days for highly liquid investments			The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents.
Restricted cash			$ 878,000	$ 878,000
Operating lease option to extent			true
Operating lease option to terminate		true	true
Impairment loss of long lived assets			$ 0	0
Conversion of convertible preferred stock into common stock upon initial public offering, shares | shares	61,992,534
Description of Income tax benefit, likelihood of realized upon ultimate settlement			greater than 50%
Laboratory and Computer Equipment [Member]
Significant Accounting Policies [Line Items]
Property and equipment, useful life			3 years
Furniture and Fixtures [Member]
Significant Accounting Policies [Line Items]
Property and equipment, useful life			5 years
Genentech [Member] | Genentech Agreement [Member]
Significant Accounting Policies [Line Items]
Number of collaboration and license agreement | Agreement			1
Collaboration and license agreement entered date			Dec. 11, 2020
Letter of Credit [Member]
Significant Accounting Policies [Line Items]
Restricted cash			$ 878,000	$ 878,000

Fair Value of Financial Asset_2

Fair Value of Financial Assets - Summary of Financial Assets Measured at Fair Value on a Recurring Basis and Level of the Fair Value Hierarchy (Detail) - Fair value on a recurring basis [Member] - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investments:
Total	$ 677,561	$ 355,520
Investments [Member]
Investments:
Total investments	230,415	313,862
Investments [Member] | US treasury bills [Member]
Investments:
Total investments	33,026	232,604
Investments [Member] | US agency securities [Member]
Investments:
Total investments	197,389	81,258
Level 1 [Member]
Investments:
Total	447,146	41,658
Level 2 [Member]
Investments:
Total	230,415	313,862
Level 2 [Member] | Investments [Member]
Investments:
Total investments	230,415	313,862
Level 2 [Member] | Investments [Member] | US treasury bills [Member]
Investments:
Total investments	33,026	232,604
Level 2 [Member] | Investments [Member] | US agency securities [Member]
Investments:
Total investments	197,389	81,258
Cash equivalents [Member] | Money market funds [Member]
Cash equivalents:
Assets, fair value	447,146	41,658
Cash equivalents [Member] | Level 1 [Member] | Money market funds [Member]
Cash equivalents:
Assets, fair value	$ 447,146	$ 41,658

Investments - Summary of Fair V

Investments - Summary of Fair Value of Available-for-Sale Investments by Type of Security (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 230,351
Unrealized Gains	64
Fair Value	230,415
Investments with a maturity of one year or less [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	50,993	$ 313,537
Unrealized Gains	26	325
Fair Value	51,019	313,862
Investments with a maturity of one to two years [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	179,358
Unrealized Gains	38
Fair Value	179,396
U.S treasury bills [Member] | Investments with a maturity of one year or less [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	29,997	232,336
Unrealized Gains	21	268
Fair Value	30,018	232,604
U.S treasury bills [Member] | Investments with a maturity of one to two years [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	3,008
Fair Value	3,008
U.S agency securities [Member] | Investments with a maturity of one year or less [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	20,996	81,201
Unrealized Gains	5	57
Fair Value	21,001	$ 81,258
U.S agency securities [Member] | Investments with a maturity of one to two years [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	176,350
Unrealized Gains	38
Fair Value	$ 176,388

Collaboration and License Arr_2

Collaboration and License Arrangement with Genentech - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020USD ($)
Collaboration And License Arrangement [Line Items]
Collaboration revenue	$ 82,654,000
Contract asset	$ 7,654,000
Genentech [Member] | Genentech Agreement [Member]
Collaboration And License Arrangement [Line Items]
Collaborative arrangement, purpose	On December 11, 2020, the Company entered into the Genentech Agreement, which granted Genentech a license to develop and commercialize RLY-1971.
Collaborative arrangement, rights and obligations	Unless Genentech elects to exercise its option to conduct the remainder of the ongoing Phase 1a Trial, the Company is responsible for the completion of this trial. Genentech is responsible for conducting all subsequent clinical development of RLY-1971. The Company is also responsible for the one-time transfer of the active pharmaceutical ingredient (“API”) and other materials related to RLY-1971 to Genentech
Non-refundable upfront payment	$ 75,000,000
Milestone payment receivable	25,000,000
Maximum additional amount received upon milestone achievement	695,000,000
Collaboration agreement transaction price	85,867,000
Non-refundable milestone payment transfer amount	5,000,000
Non-refundable milestone payment for completion amount	5,000,000
Variable consideration related to reimbursements due for research and development services	867,000
Development based milestone payments under agreement	0
Regulatory based milestone payments under agreement	0
Genentech [Member] | Genentech Agreement [Member] | Transfer of License [Member]
Collaboration And License Arrangement [Line Items]
Collaboration revenue	82,654,000
Genentech [Member] | Genentech Agreement [Member] | Research and Development Services [Member]
Collaboration And License Arrangement [Line Items]
Collaboration revenue	0
Accounts receivable	75,000,000
Genentech [Member] | Genentech Agreement [Member] | Transfer of Active Pharmaceutical Ingredients [Member]
Collaboration And License Arrangement [Line Items]
Collaboration revenue	0
Contract asset	7,654,000
Genentech [Member] | Genentech Agreement [Member] | Stand-alone Selling Prices (“SSP”) [Member]
Collaboration And License Arrangement [Line Items]
Collaboration agreement transaction price	85,867,000
Genentech [Member] | Genentech Agreement [Member] | Stand-alone Selling Prices (“SSP”) [Member] | Transfer of License [Member]
Collaboration And License Arrangement [Line Items]
Remaining performance obligations	82,654,000,000
Genentech [Member] | Genentech Agreement [Member] | Stand-alone Selling Prices (“SSP”) [Member] | Research and Development Services [Member]
Collaboration And License Arrangement [Line Items]
Remaining performance obligations	2,896,000,000
Genentech [Member] | Genentech Agreement [Member] | Stand-alone Selling Prices (“SSP”) [Member] | Transfer of Active Pharmaceutical Ingredients [Member]
Collaboration And License Arrangement [Line Items]
Remaining performance obligations	317,000,000
Genentech [Member] | Genentech Agreement [Member] | Outside US [Member]
Collaboration And License Arrangement [Line Items]
Maximum additional amount received upon milestone achievement	$ 410,000,000

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant and Equipment [Line Items]
Property and equipment	$ 16,780	$ 15,075
Less: accumulated depreciation	(10,530)	(6,981)
Total property and equipment, net	6,250	8,094
Laboratory Equipment [Member]
Property Plant and Equipment [Line Items]
Property and equipment	13,534	12,003
Leasehold Improvements [Member]
Property Plant and Equipment [Line Items]
Property and equipment	886	860
Computer Equipment [Member]
Property Plant and Equipment [Line Items]
Property and equipment	888	827
Furniture and Fixtures [Member]
Property Plant and Equipment [Line Items]
Property and equipment	895	895
Construction in Process [Member]
Property Plant and Equipment [Line Items]
Property and equipment	$ 577	$ 490

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation expense	$ 3,549	$ 2,845

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
External research and development	$ 5,099	$ 3,077
Professional services	464	336
Other	197	333
Total accrued expenses and other current liabilities	$ 5,760	$ 3,746

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Detail) - USD ($)	Jul. 08, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jul. 20, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Sale price of stock					$ 20
Outstanding convertible preferred stock converted into common shares	37,206,604		59,883,877
Convertible preferred stock outstanding		0	212,642,857
Preferred stock voting rights		The holders of the Convertible Preferred Stock had voting rights equivalent to the number of shares of common stock into which their shares of preferred stock would convert. So long as any of the Convertible Preferred Stock was outstanding, a requisite vote of the Convertible Preferred Stockholders, which was defined as a majority of the Convertible Preferred Stockholders, was required to affirm certain corporate actions, which included, but was not limited to, the disposal of assets, the acquisition of assets or a business and the authorization of additional shares of the Company’s capital. In addition, such actions required a requisite vote of the Series C preferred stockholders and a majority vote of the Series B preferred stockholders, if any of the respective preferred stock was outstanding.
Dividends declared		$ 0	$ 0
IPO [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding convertible preferred stock converted into common shares	61,992,534	0
Underwritten Public Offering [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Preferred stock convertible conversion price		$ 22.80
Outstanding convertible preferred stock converted into common shares			59,382,845
Net proceeds from exchange of stock		$ 100,000,000
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Sale price of stock	$ 22.80
Series C Preferred Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Preferred stock convertible conversion price	$ 3.027603	$ 3.21
Outstanding convertible preferred stock converted into common shares			35,097,955
Issuance of common stock in public offering, net of discounts and issuance costs of $34,707, shares			1,779,093	122,850,909
Net proceeds from exchange of stock				$ 393,587,000
Shares price, per share			$ 3.21
Proceeds from issuance costs			$ 5,661,000
Convertible preferred stock outstanding			124,630,002
Liquidation preference per share		3.21
Series C Preferred Stock [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Liquidation preference per share		22.80
Series C Preferred Stock [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Liquidation preference per share		22.80
Series A Preferred Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding convertible preferred stock converted into common shares			16,002,820
Issuance of common stock in public offering, net of discounts and issuance costs of $34,707, shares				56,824,740
Net proceeds from exchange of stock				$ 56,692,000
Convertible preferred stock outstanding			56,824,740
Liquidation preference per share		1
Series B Preferred Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding convertible preferred stock converted into common shares			8,783,102
Issuance of common stock in public offering, net of discounts and issuance costs of $34,707, shares				31,188,115
Net proceeds from exchange of stock				$ 62,876,000
Convertible preferred stock outstanding			31,188,115
Liquidation preference per share		$ 2.02

Convertible Preferred Stock - S

Convertible Preferred Stock - Summary of Convertible Preferred Stock (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jul. 08, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Preferred stock shares authorized			337,272,859
Preferred stock shares issued			212,642,857
Preferred stock shares outstanding	0		212,642,857
Carrying value			$ 537,781
Liquidation preference			$ 519,825
Common stock issuable upon conversion		37,206,604	59,883,877
Series A Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock shares authorized			56,824,740
Preferred stock shares issued			56,824,740
Preferred stock shares outstanding			56,824,740
Carrying value			$ 75,657
Liquidation preference			$ 56,825
Common stock issuable upon conversion			16,002,820
Series B Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock shares authorized			31,188,115
Preferred stock shares issued			31,188,115
Preferred stock shares outstanding			31,188,115
Carrying value			$ 62,876
Liquidation preference			$ 63,000
Common stock issuable upon conversion			8,783,102
Series C Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock shares authorized			249,260,004
Preferred stock shares issued			124,630,002
Preferred stock shares outstanding			124,630,002
Carrying value			$ 399,248
Liquidation preference			$ 400,000
Common stock issuable upon conversion			35,097,955

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Voting Rights	Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders.
Dividends declared	$ 0	$ 0
Common Stock Restriction Period	4 years
Fair value of shares, vested	$ 9,619
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based awards, authorized for issuance	0
ESPP [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based awards, authorized for issuance	1,092,532

Common Stock - Summary Of The R

Common Stock - Summary Of The Restricted Stock Activity (Detail) - Restricted Stock [Member]	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares - Beginning | shares	679,158
Shares - Vested | shares	(579,825)
Shares - Cancelled | shares	(14,844)
Shares - Ending | shares	84,489
Weighted- Average Purchase Price - Beginning | $ / shares	$ 0.21
Weighted- Average Purchase Price - Vested | $ / shares	0.26
Weighted- Average Purchase Price - Cancelled | $ / shares	0.03
Weighted- Average Purchase Price - Ending | $ / shares	$ 0.04

Common Stock - Summary of Reser

Common Stock - Summary of Reserved Shares of Common Stock (Detail) - shares	Dec. 31, 2020	Jul. 08, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding convertible preferred stock converted into common shares		37,206,604	59,883,877
Shares reserved under the compensation plan	8,026,772		8,407,169
Total shares of common stock reserved for issuance	8,026,772		68,291,046
Series A Preferred Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding convertible preferred stock converted into common shares			16,002,820
Series B Preferred Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding convertible preferred stock converted into common shares			8,783,102
Series C Preferred Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding convertible preferred stock converted into common shares			35,097,955

Share-Based Payments - Addition

Share-Based Payments - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Aug. 01, 2020	Jul. 08, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense		$ 31,960	$ 4,456
Share-based compensation arrangement by share-based payment award, vesting term		4 years
Weighted average grant date fair value of stock options granted		$ 30.14	$ 3.34
Total unrecognized compensation cost related to the unvested stock-based awards, Value		$ 69,948
Total unrecognized compensation cost related to the unvested stock-based awards, Weighted average period		2 years 7 months 9 days
Operating Income (Loss) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense		$ 25,527
2020 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Award, Number of Shares Authorized		8,026,772		0	8,376,080
2016 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Award, Number of Shares Authorized				0
Share-based Compensation Arrangement by Share-based Payment Award, Shares Purchased for Award	1,960,547
Share-based Payment Award, Award Vesting Rights		The commencement of vesting was based on the achievement of certain scientific and operational milestones during a two-year period, for which the achievement was discretionary and subject to the approval of the Company’s board of directors.

Share-Based Payments - Schedule

Share-Based Payments - Schedule of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options and Warrants Outstanding, Number of Shares Beginning Balance	5,306,176
Granted, Number of Shares	2,898,663
Exercised, Number of Shares	(297,000)
Cancelled, Number of Shares	(210,781)
Options and Warrants Outstanding, Number of Shares Ending Balance	7,697,058	5,306,176
Shares, Vested	2,148,119
Shares, Non-vested	5,548,939
Weighted Average Exercise Price Per Share, Outstanding Beginning Balance	$ 4.62
Weighted Average Exercise Price Per Share, Granted	10.90
Weighted Average Exercise Price Per Share, Exercised	4.09
Weighted Average Exercise Price Per Share, Cancelled	4.91
Weighted Average Exercise Price Per Share, Outstanding Ending Balance	6.99	$ 4.62
Weighted Average Exercise Price Per Share, Vested	4.49
Weighted Average Exercise Price Per Share, Non-vested	$ 7.96
Weighted Average Remaining Contractual Life, Outstanding	8 years 6 months	8 years 11 months 26 days
Weighted Average Remaining Contractual Life, Vested	7 years 10 months 24 days
Weighted Average Remaining Contractual Life, Non-vested	8 years 8 months 26 days
Aggregate Intrinsic Value, Outstanding Value	$ 266,050	$ 3,214
Aggregate Intrinsic Value, Vested Value	79,625
Aggregate Intrinsic Value, Non-vested Value	$ 186,425

Share-Based Payments - Schedu_2

Share-Based Payments - Schedule of Estimated Fair Value of Stock Options (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate minimum	0.40%	1.50%
Risk-free interest rate maximum	1.80%	2.50%
Expected term (in years)	6 years 3 months 18 days	6 years 3 months 18 days
Expected volatility rate minimum	73.50%	72.80%
Expected volatility rate maximum	77.60%	73.47%
Expected dividend yield	0.00%	0.00%

Share-Based Payments - Schedu_3

Share-Based Payments - Schedule of Stock-Based Compensation Expense Included In The Company's Consolidated Statements of Operations And Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 31,960	$ 4,456
Research and development expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	14,691	2,687
General and administrative expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 17,269	$ 1,769

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Income tax benefits	$ 0	$ 0
Net operating loss carryforwards, federal	174,028,000
Net operating loss carryforwards, state	192,346,000
Increase in valuation allowance	14,276,000	23,307,000
Unrecognized tax benefits	$ 0	$ 0
Description of income tax examinations	There are currently no pending tax examinations.
Tax Cuts and Jobs Act of 2017, description of corporate tax payers	Corporate taxpayers may carryback NOLs originating during 2018 through 2020 for up to five years, which was not previously allowed under the 2017 Tax Act. The CARES Act also eliminates the 80% of taxable income limitations by allowing corporate entities to fully utilize NOL carryforwards to offset taxable income in 2018, 2019 or 2020. Taxpayers may generally deduct interest up to the sum of 50% of adjusted taxable income plus business interest income (30% limit under the 2017 Tax Act) for tax years beginning January 1, 2019 and 2020. The CARES Act allows taxpayers with alternative minimum tax credits to claim a refund in 2020 for the entire amount of the credits instead of recovering the credits through refunds over a period of years, as originally enacted by the 2017 Tax Act.
CARES Act, percentage of eliminates of taxable income	80.00%
Tax Cuts and Jobs Act of 2017, maximum percentage of interest deducted by tax payers	50.00%
CARES Act, percentage of interest deducted by tax payers	30.00%
CARES Act, percentage of corporate charitable deduction limit	25.00%
CARES Act, period of qualified improvement property for cost-recovery	15 years
CARES Act, percentage of bonus depreciation	100.00%
Maximum [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryback period	5 years
Federal [Member]
Income Tax Disclosure [Line Items]
Income tax benefits	$ 0
Net operating loss carryforwards, subject to expiration	43,127,000
Net operating loss carryforwards, not subject to expiration	$ 130,901,000
Net operating loss carryforwards, beginning to expiring year	2035
Research and development tax credit carryforwards	$ 8,139,000
Research and development tax credit carryforwards, expiration year	2035
State [Member]
Income Tax Disclosure [Line Items]
Income tax benefits	$ 0
Net operating loss carryforwards, beginning to expiring year	2035
Research and development tax credit carryforwards	$ 2,699,000
Research and development tax credit carryforwards, expiration year	2030

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Expected Income Tax (Benefit) Computed Using Federal Statutory Income Tax Rate to Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory rate	21.00%	21.00%
State taxes, net of federal benefit	5.70%	7.00%
Change in valuation allowance	(27.30%)	(31.00%)
R&D credit carryovers	7.60%	4.10%
Stock-based compensation	(6.70%)	(0.90%)
Permanent differences	(0.30%)	(0.20%)
Total	0.00%	0.00%

Income Taxes - Summary of Defer

Income Taxes - Summary of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating losses	$ 48,832	$ 42,647
Tax credit carryforwards	10,270	6,309
Lease liability	6,430	6,542
Intangibles	1,469	1,498
Stock-based compensation	4,496	534
Depreciation and amortization	230	188
Other	14	13
Total gross deferred tax asset	71,741	57,731
Valuation allowance	(65,813)	(51,537)
Net deferred tax asset	5,928	6,194
Deferred tax liability
Operating lease assets	(5,928)	(6,194)
Total deferred tax liability	$ (5,928)	$ (6,194)

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Computation of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net loss	$ (52,412)	$ (75,305)
Deemed dividend resulting from extinguishment upon modification of Series C preferred stock	177,789
Net loss attributable to common stockholders	$ (230,201)	$ (75,305)
Net loss attributable to common stockholders per share, basic and diluted	$ (5.40)	$ (21.82)
Weighted average shares of common stock, basic and diluted	42,619,582	3,450,500

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Detail) - $ / shares	Jul. 08, 2020	Dec. 31, 2020
Series C Preferred Stock [Member]
Earnings Per Share Basic [Line Items]
Preferred stock convertible conversion price	$ 3.027603	$ 3.21

Net Loss Per Share - Summary _2

Net Loss Per Share - Summary of Antidilutive Securities Excluded From Computation of Earnings Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive effect	7,781,547	65,869,211
Convertible preferred stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive effect		59,883,877
Options to purchase common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive effect	7,697,058	5,306,176
Unvested restricted stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive effect	84,489	679,158

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Jun. 15, 2020USD ($)	Dec. 31, 2020USD ($)Targetshares	Dec. 31, 2019USD ($)shares	Jul. 08, 2020shares
Commitments and Contingencies Disclosure [Line Items]
Outstanding convertible preferred stock converted into common shares | shares			59,883,877	37,206,604
Research and development expense		$ 99,862,000	$ 70,306,000
Accrued expenses		5,760,000	3,746,000
DE Shaw Research [Member]
Commitments and Contingencies Disclosure [Line Items]
Research and development expense		6,376,000	1,500,000
Accrued expenses		$ 1,500,000	372,000
DE Shaw Research [Member] | License Agreement Terms [Member]
Commitments and Contingencies Disclosure [Line Items]
Outstanding convertible preferred stock converted into common shares | shares		3,281,253
Research and development arrangement, annual fee	$ 7,900,000		1,000,000
Research and development arrangement, term of contract		3 years
Research and development arrangement, expiration date	Aug. 16, 2025
Milestone payment Due		$ 7,250,000
Maximum additional amount received upon milestone achievement		6,250,000
DE Shaw Research [Member] | Lease Agreement
Commitments and Contingencies Disclosure [Line Items]
Milestone payment Due		1,500,000	0
Other Third Parties [Member]
Commitments and Contingencies Disclosure [Line Items]
Research and development expense		2,704,000	3,493,000
Other Third Parties [Member] | License Agreement Terms [Member]
Commitments and Contingencies Disclosure [Line Items]
Milestone payment Due		$ 0	$ 0
Number of milestone targets | Target		4
Maximum [Member] | DE Shaw Research [Member] | License Agreement Terms [Member]
Commitments and Contingencies Disclosure [Line Items]
Agreement renewal period		1 year
Potential development milestone payments		$ 7,300,000
Maximum [Member] | Other Third Parties [Member] | License Agreement Terms [Member]
Commitments and Contingencies Disclosure [Line Items]
Potential development milestone payments		7,000,000
Minimum [Member] | Other Third Parties [Member] | License Agreement Terms [Member]
Commitments and Contingencies Disclosure [Line Items]
Potential development milestone payments		$ 4,000,000
Series A Preferred Stock [Member]
Commitments and Contingencies Disclosure [Line Items]
Outstanding convertible preferred stock converted into common shares | shares			16,002,820
Series A Preferred Stock [Member] | DE Shaw Research [Member] | License Agreement Terms [Member]
Commitments and Contingencies Disclosure [Line Items]
Shares held | shares			9,999,999
Series C Preferred Stock [Member]
Commitments and Contingencies Disclosure [Line Items]
Outstanding convertible preferred stock converted into common shares | shares			35,097,955
Series C Preferred Stock [Member] | DE Shaw Research [Member] | License Agreement Terms [Member]
Commitments and Contingencies Disclosure [Line Items]
Shares held | shares			1,557,875

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands	1 Months Ended			12 Months Ended
	Sep. 30, 2020ft²	Dec. 31, 2017ft²	Nov. 30, 2015	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Jan. 31, 2018ft²
Operating Leased Assets [Line Items]
Operating lease option to terminate			true	true
Letter of credit				$ 878
Letter of credit expiry date				Sep. 30, 2028
Operating lease, payments				$ 4,878	$ 2,602
Weighted-average remaining lease term				8 years 3 months 18 days	9 years 3 months 18 days
Weighted-average discount rate				10.40%	10.40%
215 First Street [Member]
Operating Leased Assets [Line Items]
Operating lease agreement expiration date			2020-12
399 Binney Street [Member]
Operating Leased Assets [Line Items]
Operating lease agreement expiration date	2029-04	2029-04
Land subject to ground leases | ft²	1,824	44,336				44,807

Leases - Schedule of Operating

Leases - Schedule of Operating Leases Presentation in Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease assets	$ 22,579	$ 23,560
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	rlay:OperatingLeaseAssetsMember	rlay:OperatingLeaseAssetsMember
Current operating lease liabilities	$ 1,521	$ 1,249
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	rlay:OperatingLeaseLiabilitiesMember	rlay:OperatingLeaseLiabilitiesMember
Non-current operating lease liabilities	$ 22,901	$ 23,583
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	rlay:OperatingLeaseLiabilitiesNetOfCurrentPortionMember	rlay:OperatingLeaseLiabilitiesNetOfCurrentPortionMember
Total lease liabilities	$ 24,422	$ 24,832

Leases - Summary of Operating L

Leases - Summary of Operating Lease Presentation in Consolidated Statements of Operations and Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating Leased Assets [Line Items]
Operating lease costs	$ 4,021	$ 3,797
Research and development expenses [Member]
Operating Leased Assets [Line Items]
Operating lease costs	3,273	3,216
General and administrative expenses [Member]
Operating Leased Assets [Line Items]
Operating lease costs	$ 748	$ 581

Leases - Summary of Future Mini

Leases - Summary of Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2021	$ 3,985
2022	4,134
2023	4,254
2024	4,377
2025	4,503
Thereafter	15,959
Total lease payments	37,212
Less: interest	(12,790)
Present value of operating lease liabilities	$ 24,422	$ 24,832

Employee Benefits - Additional

Employee Benefits - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Compensation And Retirement Disclosure [Abstract]
Employer matching contribution	$ 590

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - Third Rock Venture [Member] - Consulting And Management Services [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Related Party Expense	$ 0	$ 200
Due To Related Parties	$ 0	$ 80