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Cover Page - shares	6 Months Ended
Cover Page - shares	Jun. 30, 2020	Jul. 31, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Entity Interactive Data Current	Yes
Entity Central Index Key	0001733294
Current Fiscal Year End Date	--12-31
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2020
Entity Registrant Name	GENERATION BIO CO.
Trading Symbol	GBIO
Entity File Number	001-39319
Entity Incorporation, State or Country Code	DE
Entity Current Reporting Status	No
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Address, Address Line One	301 Binney Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	655-7500
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, $0.0001 Par Value
Entity Common Stock, Shares Outstanding		46,427,673
Entity Ex Transition Period	false

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 171,691	$ 15,076
Marketable securities	129,395
Tenant receivable		448
Prepaid expenses and other current assets	5,091	2,577
Restricted cash		55
Total current assets	306,177	18,156
Property and equipment, net	22,822	21,845
Restricted cash, noncurrent	2,052	2,052
Deferred offering costs		87
Other long-term assets	151
Total assets	331,202	42,140
Current liabilities:
Accounts payable	2,624	2,251
Accrued expenses and other current liabilities	8,912	6,907
Total current liabilities	11,536	9,158
Deferred rent, net of current portion	15,513	15,981
Total liabilities	27,049	25,139
Commitments and contingencies (Note 9)
Convertible preferred stock (Series A, B and C), $0.0001 par value; no shares and 26,425,664 shares authorized at June 30, 2020 and December 31, 2019, respectively; no shares and 26,425,664 shares issued and outstanding at June 30, 2020 and December 31, 2019, respectively		115,593
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 5,000,000 and no shares authorized at June 30, 2020 and December 31, 2019, respectively; no shares issued or outstanding
Common stock, $0.0001 par value; 150,000,000 and 46,750,000 shares authorized at June 30, 2020 and December 31, 2019, respectively; 46,237,096 and 6,976,077 shares issued at June 30, 2020 and December 31, 2019, respectively; 45,028,024 and 5,270,889 shares outstanding at June 30, 2020 and December 31, 2019, respectively	5	1
Additional paid-in capital	448,052	9,859
Accumulated other comprehensive loss	(4)
Accumulated deficit	(143,900)	(108,452)
Total stockholders' equity (deficit)	304,153	(98,592)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 331,202	$ 42,140

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Convertible preferred stock, par value per share	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized	0	26,425,664
Convertible preferred stock, shares issued	0	26,425,664
Convertible preferred stock, shares outstanding	0	26,425,664
Preferred stock, par value per share	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	46,750,000
Common stock, shares issued	46,237,096	6,976,077
Common stock, shares outstanding	45,028,024	5,270,889

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses:
Research and development	$ 13,456	$ 12,237	$ 26,850	$ 23,956
General and administrative	4,308	3,098	8,950	5,855
Total operating expenses	17,764	15,335	35,800	29,811
Loss from operations	(17,764)	(15,335)	(35,800)	(29,811)
Other income (expense):
Interest income and other income (expense), net	33	303	352	685
Net loss and net loss attributable to common stockholders	$ (17,731)	$ (15,032)	$ (35,448)	$ (29,126)
Net loss per share attributable to common stockholders, basic and diluted	$ (1.50)	$ (3.30)	$ (4.10)	$ (6.59)
Weighted average common shares outstanding, basic and diluted	11,801,704	4,557,517	8,648,358	4,421,601
Comprehensive loss:
Net loss	$ (17,731)	$ (15,032)	$ (35,448)	$ (29,126)
Other comprehensive income (loss):
Unrealized gains (losses) on marketable securities	(4)	6	(4)	20
Comprehensive loss	$ (17,735)	$ (15,026)	$ (35,452)	$ (29,106)

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance, convertible preferred stock at Dec. 31, 2018	$ 115,593
Beginning balance, convertible preferred stock, shares at Dec. 31, 2018	26,425,664
Beginning balance at Dec. 31, 2018	$ (41,591)	$ 1	$ 5,552	$ (9)	$ (47,135)
Beginning balance, shares at Dec. 31, 2018		4,054,475
Issuance of common stock upon exercise of stock options	9		9
Issuance of common stock upon exercise of stock options, shares		14,861
Vesting of restricted common stock, shares		546,047
Stock-based compensation expense	2,042		2,042
Unrealized gains (losses) on marketable securities	20			20
Net loss	(29,126)				(29,126)
Ending balance, convertible preferred stock at Jun. 30, 2019	$ 115,593
Ending balance, convertible preferred stock, shares at Jun. 30, 2019	26,425,664
Ending balance at Jun. 30, 2019	$ (68,646)	$ 1	7,603	11	(76,261)
Ending balance, shares at Jun. 30, 2019		4,615,383
Beginning balance, convertible preferred stock at Mar. 31, 2019	$ 115,593
Beginning balance, convertible preferred stock, shares at Mar. 31, 2019	26,425,664
Beginning balance at Mar. 31, 2019	$ (54,669)	$ 1	6,554	5	(61,229)
Beginning balance, shares at Mar. 31, 2019		4,355,671
Vesting of restricted common stock, shares		259,712
Stock-based compensation expense	1,049		1,049
Unrealized gains (losses) on marketable securities	6			6
Net loss	(15,032)				(15,032)
Ending balance, convertible preferred stock at Jun. 30, 2019	$ 115,593
Ending balance, convertible preferred stock, shares at Jun. 30, 2019	26,425,664
Ending balance at Jun. 30, 2019	$ (68,646)	$ 1	7,603	11	(76,261)
Ending balance, shares at Jun. 30, 2019		4,615,383
Beginning balance, convertible preferred stock at Dec. 31, 2019	$ 115,593
Beginning balance, convertible preferred stock, shares at Dec. 31, 2019	26,425,664
Beginning balance at Dec. 31, 2019	$ (98,592)	$ 1	9,859		(108,452)
Beginning balance, shares at Dec. 31, 2019		5,270,889
Issuance of Series C convertible preferred stock, net of issuance costs of $2,640, shares	19,936,296
Issuance of Series C convertible preferred stock, net of issuance costs of $2,640	$ 108,832
Conversion of convertible preferred stock into common stock upon initial public offering, convertible preferred stock	$ (224,425)
Conversion of convertible preferred stock into common stock upon initial public offering, convertible preferred stock, shares	(46,361,960)
Conversion of convertible preferred stock into common stock upon initial public offering	$ 224,425	$ 3	224,422
Conversion of convertible preferred stock into common stock upon initial public offering, shares		27,094,085
Issuance of common stock upon initial public offering, net of issuance costs of $3,185	210,715	$ 1	210,714
Issuance of common stock upon initial public offering, net of issuance costs of $3,185, shares		12,105,263
Issuance of common stock upon exercise of stock options	185		185
Issuance of common stock upon exercise of stock options, shares		40,263
Vesting of restricted common stock, shares		517,524
Stock-based compensation expense	2,872		2,872
Unrealized gains (losses) on marketable securities	(4)			(4)
Net loss	$ (35,448)				(35,448)
Ending balance, convertible preferred stock, shares at Jun. 30, 2020	0
Ending balance at Jun. 30, 2020	$ 304,153	$ 5	448,052	(4)	(143,900)
Ending balance, shares at Jun. 30, 2020		45,028,024
Beginning balance, convertible preferred stock at Mar. 31, 2020	$ 224,425
Beginning balance, convertible preferred stock, shares at Mar. 31, 2020	46,361,960
Beginning balance at Mar. 31, 2020	$ (114,651)	$ 1	11,517		(126,169)
Beginning balance, shares at Mar. 31, 2020		5,570,652
Conversion of convertible preferred stock into common stock upon initial public offering, convertible preferred stock	$ (224,425)
Conversion of convertible preferred stock into common stock upon initial public offering, convertible preferred stock, shares	(46,361,960)
Conversion of convertible preferred stock into common stock upon initial public offering	$ 224,425	$ 3	224,422
Conversion of convertible preferred stock into common stock upon initial public offering, shares		27,094,085
Issuance of common stock upon initial public offering, net of issuance costs of $3,185	210,715	$ 1	210,714
Issuance of common stock upon initial public offering, net of issuance costs of $3,185, shares		12,105,263
Issuance of common stock upon exercise of stock options	31		31
Issuance of common stock upon exercise of stock options, shares		5,434
Vesting of restricted common stock, shares		252,590
Stock-based compensation expense	1,368		1,368
Unrealized gains (losses) on marketable securities	(4)			(4)
Net loss	$ (17,731)				(17,731)
Ending balance, convertible preferred stock, shares at Jun. 30, 2020	0
Ending balance at Jun. 30, 2020	$ 304,153	$ 5	$ 448,052	$ (4)	$ (143,900)
Ending balance, shares at Jun. 30, 2020		45,028,024

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Common Stock [Member] \| IPO [Member]
Stock issuance of costs	$ 3,185	$ 3,185
Series C Convertible Preferred Stock [Member]
Stock issuance of costs		$ 2,640

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (35,448)	$ (29,126)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	2,872	2,042
Depreciation and amortization expense	1,502	525
Accretion of discount on marketable securities		(281)
Changes in operating assets and liabilities:
Tenant receivable	448	(2,048)
Prepaid expenses and other current assets	(2,514)	(447)
Other noncurrent assets	(151)
Accounts payable	799	953
Accrued expenses and other current liabilities	(304)	1,296
Deferred rent	(468)	10,330
Net cash used in operating activities	(33,264)	(16,756)
Cash flows from investing activities:
Purchases of property and equipment	(2,223)	(13,203)
Purchases of marketable securities	(129,399)	(20,789)
Sales and maturities of marketable securities		73,680
Net cash provided by (used in) investing activities	(131,622)	39,688
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs incurred and paid in current period	108,854
Proceeds from initial public offering of common stock, net of commissions and underwriting discounts	213,900
Proceeds from exercise of stock options	185	9
Payment of initial public offering costs	(1,493)
Net cash provided by financing activities	321,446	9
Net increase in cash, cash equivalents and restricted cash	156,560	22,941
Cash, cash equivalents and restricted cash at beginning of period	17,183	9,466
Cash, cash equivalents and restricted cash at end of period	173,743	32,407
Supplemental Cash Flow Information [Abstract]
Conversion of convertible preferred stock to common stock	224,425
Public offering costs included in accounts payable or accrued expenses	1,692
Purchases of property and equipment included in accounts payable and accrued expenses	$ 900	$ 3,579

Nature of the Business and Basis of Presentation

6 Months Ended

Jun. 30, 2020

Accounting Policies [Abstract]

Nature of the Business and Basis of Presentation

The Company was incorporated on October 21, 2016 as Torus Therapeutics, Inc. and subsequently changed its name to Generation Bio Co. (the “Company” or “Generation Bio”). The Company is an innovative genetic medicines company creating a new class of gene therapy utilizing its proprietary

non-viral

gene therapy platform to provide durable, redosable treatments for millions of patients living with rare and prevalent diseases. The Company’s

non-viral

gene therapy platform incorporates its high-capacity DNA construct called closed-ended DNA (“ceDNA”), its cell-targeted lipid nanoparticle delivery system (“ctLNP”) and its established, scalable capsid-free manufacturing process. Using its approach, the Company is developing novel gene therapies to provide targeted delivery of genetic payloads that include large and multiple genes to a range of tissues across a broad array of diseases. The Company is also engineering its gene therapies to be redosable, which may enable individualized patient titration to reach the desired therapeutic expression and to maintain efficacy throughout a patient’s life. The Company is headquartered in Cambridge, Massachusetts.

The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, the ability to establish clinical- and commercial-scale manufacturing processes, the impact of the

COVID-19

pandemic and the ability to secure additional capital to fund operations. Programs currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization of a product. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

On June 16, 2020, the Company completed its initial public offering (“IPO”) pursuant to which it issued and sold 12,105,263 shares of its common stock, including 1,578,947 shares pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $19.00 per share, resulting in net proceeds of $210.7 million, after deducting underwriting discounts and commissions and other offering expenses. Upon the closing of the IPO,

all of

the Company’s outstanding convertible preferred stock automatically converted into shares of common stock.

The accompanying consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. Since inception, the Company has funded its operations with proceeds from the sales of instruments convertible into convertible preferred stock (which converted into convertible preferred stock in 2017)

the sale of convertible preferred stock, and most recently, with proceeds from

the sale of common stock in

the IPO completed in June 2020. The Company has incurred recurring losses, including net losses of

35.4 million for the six months ended June 30, 2020 and $61.3 million for the year ended December 31, 2019. As of June 30, 2020, the Company had an accumulated deficit of $143.9 million. The Company expects to continue to generate operating losses in the foreseeable future. As of August

, 2020, the issuance date of

the

interim condensed consolidated financial statements, the Company expects that its cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months.

The Company will need to obtain additional funding through public or private equity offerings, debt financings, collaborations, strategic alliances and/or licensing arrangements. 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 collaborative or strategic alliances or licensing arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. Arrangements with collaborators or others may require the Company to relinquish rights to certain of its technologies or programs. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, pipeline expansion or commercialization efforts, which could adversely affect its business prospects. Although management will continue to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations when needed or at all.

The accompanying consolidated financial statements reflect the operations of the Company and the Company’s wholly owned subsidiary, Generation Bio Securities Corporation. Intercompany balances and transactions have been eliminated in consolidation. The accompanying consolidated financial statements have been prepared in conformity with generally accepted accounting principles (“GAAP”) in the United States of America. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

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 financial statements and the reported amounts of revenue and 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 expenses and stock-based compensation expense. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results may differ from those estimates or assumptions.

Unaudited interim financial information

The balance sheet at December 31, 2019 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited financial statements as of June 30, 2020 and for the three and six months ended June 30, 2020 and 2019 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with the Company’s audited financial statements included in the Company’s Registration Statement on Form

S-1

(File

No. 333-238608)

on file with SEC. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair

presentation

of the Company’s financial position as of June 30, 2020, the results of operations for the three and six months ended June 30, 2020 and 2019, and cash flows for the six months ended June 30, 2020 and 2019 have been made. The results of operations for the

ree and

six months ended June 30, 2020 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2020 or any other period.

Concentrations of credit risk and of significant suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, and marketable securities. The Company believes it is not exposed to significant credit risk due to the financial strength of the depository institutions in which the cash and cash equivalents are held. The Company maintains its cash equivalents in money market funds that invest in U.S. treasury securities. The Company’s cash equivalents and marketable securities as of June 30, 2020 consisted of money market funds, U.S government treasury securities, U.S. government agency bonds, commercial paper and corporate debt securities. The Company has adopted an investment policy that limits the amounts the Company may invest in the securities of single issuer with the exclusion of the U.S. government. The Company has not experienced any credit losses and does not believe that it is subject to significant credit risk.

The Company is dependent on a small number of third-party suppliers for its drug substance and drug product. In particular, the Company relies, and expects to continue to rely, on third-party suppliers for certain materials and components required for the production of any product candidates it may develop for its programs. These programs could be adversely affected by a significant interruption in the supply process.

Fair value measurements

Certain assets and liabilities of the Company 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 financial 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.

The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities.

Recently adopted accounting pronouncements

In August 2018, the FASB issued ASU

2018-13,

Fair Value Measurement (Topic 820): Disclosure Requirements for Fair Value Measurement. The new standard added, modified or removed disclosure requirements under Topic 820 for clarity and consistency. ASU

2018-13

is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company adopted ASU

2018-03

on January 1, 2020 and the adoption did not have a material impact on its consolidated financial statements.

Recently issued accounting pronouncements

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 not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application 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.

In February 2016, the FASB issued ASU

2016-02,

Leases (Topic 842). The new standard requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. In July 2018, the FASB issued ASU

2018-11,

which provides entities with an additional transition method to adopt Topic 842. Under the new transition method, an entity initially applies the new lease requirements at the adoption date, not the earliest period presented, and recognizes a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption. For public entities, the guidance was effective for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years. For nonpublic entities, the guidance was effective for annual reporting periods beginning after December 15, 2019. Early adoption is permitted for all entities. In November 2019, the FASB issued ASU

2019-10,

which deferred the effective date for nonpublic entities to annual reporting periods beginning after December 15, 2020, and interim periods within fiscal years beginning after December 15, 2021. In June 2020, the FASB issued ASU

2020-05,

which grants a

one-year

effective-date delay for nonpublic entities to annual reporting periods beginning after December 15, 2021 and to interim periods within fiscal years beginning after December 15, 2022. Early adoption continues to be allowed. The Company

plan

adopt ASU

2016-02

on January 1, 2021 using the modified retrospective approach transition method as of the date of adoption such that prior periods will not be restated. The Company will also elect a package of practical expedients, under which an entity need not reassess whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases, or initial direct costs for any existing leases. The adoption of the new standard is expected to result in the recognition of material liabilities and

right-of-use

assets, however, the Company has not completed its assessment.

In June 2016, the FASB issued ASU

2016-13,

Financial Instruments – Credit Losses (Topic 326). The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as

available-for-sale.

The standard eliminates the probable initial recognition threshold and requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial assets to present the net amount expected to be collected. For public entities, the guidance is effective for annual reporting periods beginning after December 15, 2019 and for interim periods within those fiscal years. For nonpublic entities, the guidance was effective for annual reporting periods beginning after December 15, 2020. Early adoption is permitted for all entities. In November 2019, the FASB issued ASU

2019-10,

which deferred the effective date for nonpublic entities to annual reporting periods beginning after December 15, 2022, including interim periods within those fiscal years. The Company is currently evaluating when to adopt the guidance and the impact the guidance will have on its consolidated financial statements.

Fair Value of Financial Assets

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets

As of June 30, 2020, marketable securities by security type consisted of the following:


			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
	(in thousands)
U.S. treasury securities	$	59,943	$	2	$	(1	)	$	59,944
U.S. government agency bonds		11,990		—		(1	)		11,989
Commercial paper		44,862		—		—			44,862
Corporate debt securities		12,604		1		(5	)		12,600

Totals	$	129,399	$	3	$	(7	)	$	129,395

As of June 30, 2020, marketable securities consisted of investments that mature within one year. The Company did not have marketable securities at December 31, 2019.

The following tables present the Company’s assets that are measured at fair value on a recurring basis and indicate the level within the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value, which is described further within Note 2, Summary of Significant Accounting Policies:


	Fair Value Measurements at June 30, 2020 Using:
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash equivalents:
Money market funds	$	169,350	$	—	$	—	$	169,350
Marketable securities:
U.S. treasury securities		—		59,944		—		59,944
U.S. government agency bonds		—		11,989		—		11,989
Commercial paper		—		44,862		—		44,862
Corporate debt securities		—		12,600		—		12,600

Totals	$	169,350	$	129,395	$	—	$	298,745


	Fair Value Measurements at December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash equivalents:
Money market funds	$	15,076	$	—	$	—	$	15,076

Totals	$	15,076	$	—	$	—	$	15,076

Money market funds were valued based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. The Company’s marketable securities, which consisted of U.S. treasury securities, U.S. government agency bonds, commercial paper and corporate debt securities were valued using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Accrued Expenses and Other Current Liabilities

6 Months Ended

Jun. 30, 2020

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:


	June 30, 2020		December 31, 2019
	(in thousands)
Accrued employee compensation and benefits	$	2,852	$	3,255
Accrued external research and development expenses		1,304		1,344
Accrued professional fees		2,383		619
Deferred rent		1,373		1,370
Accrued property and equipment		786		—
Other		214		319

	$	8,912	$	6,907

Convertible Preferred Stock

6 Months Ended

Jun. 30, 2020

Temporary Equity Disclosure [Abstract]

Convertible Preferred Stock

The Company had issued Series A convertible preferred stock (the “Series A”), Series B convertible preferred stock (the “Series B”) and Series C convertible preferred stock (the “Series C”). Collectively the Series A, Series B and Series C are referred to as the Preferred Stock.

On January 9, 2020, the Company issued and sold 19,936,296 shares of Series C at a price of $5.5914 per share for gross proceeds of $111.5 million. The Company incurred issuance costs in connection with this transaction of $2.6 million.

Upon the closing of the IPO in June 2020, the Company’s Preferred Stock automatically converted into 27,094,085 shares of common stock.

Equity

6 Months Ended

Jun. 30, 2020

Equity [Abstract]

Equity

As of June 30, 2020, the Company’s amended and restated certificate of incorporation authorizes the Company to issue 150,000,000 shares of common stock, par value $0.0001 per share, and 5,000,000 shares of preferred stock, par value $0.0001 per share, all of which preferred stock is undesignated.

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 not entitled to receive dividends, unless declared by the board of directors.

Stock-Based Awards

6 Months Ended

Jun. 30, 2020

Share-based Payment Arrangement [Abstract]

Stock-Based Awards

Stock incentive plans

The Company’s 2017 Stock Incentive Plan (the “2017 Plan”) provided for the Company to grant incentive stock options or nonstatutory stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. In January 2020, the number of shares of common stock authorized for issuance under the 2017 Plan was increased from 8,407,405 shares to 10,275,717 shares.

In May 2020 the Company’s board of directors adopted, and in June 2020 the Company’s stockholders approved, the 2020 Stock Incentive Plan (the “2020 Plan” and, together with the 2017 Plan the “Plans”), which became effective on June 11, 2020. The 2020 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. Upon effectiveness of the 2020 Plan, the number of shares of common stock that was reserved for issuance under the 2020 Plan was the sum of (1) 2,547,698 shares; plus (2) the number of shares (up to a maximum of 7,173,014 shares) as

was

equal to the sum of (x) the number of shares of common stock reserved for issuance under the 2017 Plan that remained available for grant under the 2017 Plan on June 11, 2020 and (y) the number of shares of common stock subject to outstanding awards granted under the 2017 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right; plus (3) an annual increase, to be added on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2021 and continuing until, and including, the fiscal year ending December 31, 2030, equal to the lesser of (i) 4% of the number of shares of common stock outstanding on such date, and (ii) an amount determined by the board of directors. Upon the effectiveness of the 2020 Plan, the Company ceased granting additional awards under the 2017 Plan.

The Plans are administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions on any award under the Plans are determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted under the Plans with service-based vesting conditions generally vest over four years and expire after ten years. The exercise price for stock options granted is not less than the fair value of common stock as of the date of grant. Prior to the Company’s IPO, fair value of common stock was determined by the board of directors. Subsequent to the IPO, fair value of common stock will be based on quoted market prices.

As of June 30, 2020, 3,061,794 shares remained available for future issuance under the 2020 Plan. Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards under the 2020 Plan.

Grant of stock options

During the six months ended June 30, 2020, the Company granted

service-based

options to certain employees, directors and consultants for the purchase of 1,659,661 shares of common stock with a weighted average grant date fair value of $7.07

per share

that vest over approximately four years.

During the six months ended June 30, 2020, the Company granted performance-based options to certain employees, directors and consultants for the purchase of 717,154 shares of common stock with a weighted average grant date fair value of $3.26

per share that vest upon the achievement of specified milestones

Employee stock purchase plan

In May 2020 the Company’s board of directors adopted, and in June 2020 the Company’s stockholders approved, the 2020 Employee Stock Purchase Plan (the “2020 ESPP”), which became effective June 11, 2020. The 2020 ESPP will be administered by the Company’s board of directors or by a committee appointed by the board of directors. The 2020 ESPP initially provides participating employees with the opportunity to purchase up to an aggregate of 481,231 shares of common stock. The number of shares of common stock reserved for issuance under the 2020 ESPP will automatically increase on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2021 and continuing for each fiscal year until, and including the fiscal year commencing on, January 1, 2030, in an amount equal to the lowest of (1) 1,302,157 shares of common stock, (2) 1% of the number of shares of common stock outstanding on such date, and (3) an amount determined by the board of directors. No offering periods have commenced under the 2020 ESPP and 481,231 shares remain available for issuance.

Stock-based compensation

Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
	(in thousands)
Research and development expenses	$	936	$	675	$	1,763	$	1,351
General and administrative expenses		432		374		1,109		691

	$	1,368	$	1,049	$	2,872	$	2,042

As of June 30, 2020, total unrecognized compensation cost related to unvested stock-based awards was $19.2 million, which is expected to be recognized over a weighted average period of 3.1 years. Additionally, as of June 30, 2020, the Company has unrecognized compensation cost related to unvested stock-based awards with performance-based vesting conditions for which performance has not been deemed probable of $2.3 million.

Net Loss per Share

6 Months Ended

Jun. 30, 2020

Earnings Per Share [Abstract]

Net Loss per Share

The following potential dilutive securities, presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact:


	June 30,
	2020		2019
Convertible preferred stock (as converted to common stock)		—		14,961,027
Unvested restricted common stock		1,209,072		2,218,595
Stock options to purchase common stock		5,439,546		2,494,444

		6,648,618		19,674,066

Commitments and Contingencies

6 Months Ended

Jun. 30, 2020

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

The Company leases its office and laboratory space under a noncancelable operating lease that was entered into in August 2018, as amended in

June 2020

, and expires in 2029. The Company has an option to extend for one additional term of five years at the greater of the then-current base rent, or the then-current fair market value. The lease agreement includes provisions for a free-rent period and annual rent increases, which are accrued or deferred as appropriate such that rent expense for the lease is recognized on a straight-line basis over the lease term. The Company is responsible for real estate taxes, maintenance, and other operating expenses applicable to the leased premises. The lease provides for a tenant improvement allowance, at the cost of the lessor, not to exceed $14.7 million. Costs incurred by the Company for tenant improvements but not yet reimbursed by the landlord are presented on the accompanying consolidated balance sheets as tenant receivable. The Company posted a customary letter of credit in the amount of approximately $2.1 million as a security deposit. The letter of credit is subject to increase if the Company were to sublease any portion of the leased premises.

Rent expense for the three months ended June 30, 2020 and 2019 was $1.9 million and $1.3 million, respectively. Rent expense for the six months ended June 30, 2020 and 2019 was $3.7 million and $3.5 million, respectively.

Future minimum lease payments as of June 30, 2020 are as follows:


Year Ending December 31,	(in thousands)
2020 (remaining 6 months)	$	3,488
2021		7,053
2022		7,251
2023		7,441
2024		7,679
Thereafter		35,451

	$	68,363

401(k) Plan

The Company has a defined-contribution plan under Section 401(k) of the Internal Revenue Code of 1986 (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.

As currently established, the Company is not required to make, and to date has not made, any contributions to the 401(k) Plan.

Indemnification agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, contract research organizations, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. The Company has not incurred any material costs as a result of such indemnifications and is not currently aware of any indemnification claims.

Legal proceedings

The Company, from time to time, may be party to litigation arising in the ordinary course of business. The Company was not subject to any material legal proceedings during the three and six months ended June 30, 2020.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2020

Accounting Policies [Abstract]

Use of estimates

Unaudited interim financial information

S-1

(File

No. 333-238608)

on file with SEC. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair

presentation

ree and

six months ended June 30, 2020 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2020 or any other period.

Concentrations of credit risk and of significant suppliers

Fair value measurements

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Recently issued accounting pronouncements

In February 2016, the FASB issued ASU

2016-02,

2018-11,

2019-10,

2020-05,

which grants a

one-year

plan

adopt ASU

2016-02

right-of-use

assets, however, the Company has not completed its assessment.

In June 2016, the FASB issued ASU

2016-13,

Financial Instruments – Credit Losses (Topic 326). The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as

available-for-sale.

2019-10,

Fair Value of Financial Assets (Tables)

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

Summary of marketable securities

As of June 30, 2020, marketable securities by security type consisted of the following:


			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
	(in thousands)
U.S. treasury securities	$	59,943	$	2	$	(1	)	$	59,944
U.S. government agency bonds		11,990		—		(1	)		11,989
Commercial paper		44,862		—		—			44,862
Corporate debt securities		12,604		1		(5	)		12,600

Totals	$	129,399	$	3	$	(7	)	$	129,395

Summary of assets measured at fair value on a recurring basis


	Fair Value Measurements at June 30, 2020 Using:
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash equivalents:
Money market funds	$	169,350	$	—	$	—	$	169,350
Marketable securities:
U.S. treasury securities		—		59,944		—		59,944
U.S. government agency bonds		—		11,989		—		11,989
Commercial paper		—		44,862		—		44,862
Corporate debt securities		—		12,600		—		12,600

Totals	$	169,350	$	129,395	$	—	$	298,745


	Fair Value Measurements at December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash equivalents:
Money market funds	$	15,076	$	—	$	—	$	15,076

Totals	$	15,076	$	—	$	—	$	15,076

Accrued Expenses and Other Current Liabilities (Tables)

6 Months Ended

Jun. 30, 2020

Payables and Accruals [Abstract]

Summary of Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:


	June 30, 2020		December 31, 2019
	(in thousands)
Accrued employee compensation and benefits	$	2,852	$	3,255
Accrued external research and development expenses		1,304		1,344
Accrued professional fees		2,383		619
Deferred rent		1,373		1,370
Accrued property and equipment		786		—
Other		214		319

	$	8,912	$	6,907

Stock-Based Awards (Tables)

6 Months Ended

Jun. 30, 2020

Share-based Payment Arrangement [Abstract]

Summary of stock-based compensation expense was classified in the statements of operations and comprehensive loss

Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
	(in thousands)
Research and development expenses	$	936	$	675	$	1,763	$	1,351
General and administrative expenses		432		374		1,109		691

	$	1,368	$	1,049	$	2,872	$	2,042

Net Loss per Share (Tables)

6 Months Ended

Jun. 30, 2020

Earnings Per Share [Abstract]

Summary of potential dilutive securities, presented based on amounts outstanding


	June 30,
	2020		2019
Convertible preferred stock (as converted to common stock)		—		14,961,027
Unvested restricted common stock		1,209,072		2,218,595
Stock options to purchase common stock		5,439,546		2,494,444

		6,648,618		19,674,066

Commitments and Contingencies (Tables)

6 Months Ended

Jun. 30, 2020

Commitments and Contingencies Disclosure [Abstract]

Summary of future minimum lease payments

Future minimum lease payments as of June 30, 2020 are as follows:


Year Ending December 31,	(in thousands)
2020 (remaining 6 months)	$	3,488
2021		7,053
2022		7,251
2023		7,441
2024		7,679
Thereafter		35,451

	$	68,363

Nature of the Business and Basis of Presentation - Additional information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 16, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Date of incorporation				Oct. 21, 2016
Net loss		$ (17,731)	$ (15,032)	$ (35,448)	$ (29,126)	$ (61,300)
Used in BS		$ (143,900)		$ (143,900)		$ (108,452)
Common Stock [Member]
Shares issued during the period		12,105,263		12,105,263
Common Stock [Member] \| IPO [Member]
Shares issued during the period	12,105,263
Shares issued price	$ 19.00
Sale of Stock, Consideration Received on Transaction	$ 210,700
Common Stock [Member] \| Over-Allotment Option [Member]
Shares issued during the period	1,578,947

- Definition

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

+ References + Details

Fair Value of Financial Assets - Summary of marketable securities (Detail) - Fair Value, Recurring [Member] $ in Thousands	Jun. 30, 2020 USD ($)
Marketable Securities [Line Items]
Amortized cost	$ 129,399
Gross unrealized gain	3
Gross unrealized losses	(7)
Estimated fair value	129,395
U.S. treasury securities
Marketable Securities [Line Items]
Amortized cost	59,943
Gross unrealized gain	2
Gross unrealized losses	(1)
Estimated fair value	59,944
U.S. government agency bonds
Marketable Securities [Line Items]
Amortized cost	11,990
Gross unrealized losses	(1)
Estimated fair value	11,989
Commercial paper
Marketable Securities [Line Items]
Amortized cost	44,862
Estimated fair value	44,862
Corporate debt securities
Marketable Securities [Line Items]
Amortized cost	12,604
Gross unrealized gain	1
Gross unrealized losses	(5)
Estimated fair value	$ 12,600

Fair Value of Financial Assets - Summary of assets measured at fair value on a recurring basis (Detail) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Marketable securities:
Marketable securities	$ 129,395
Totals	298,745	$ 15,076
Level 1
Marketable securities:
Totals	169,350	15,076
Level 2
Marketable securities:
Totals	129,395
Money Market Funds
Cash equivalents:
Cash equivalents	169,350	15,076
Money Market Funds \| Level 1
Cash equivalents:
Cash equivalents	169,350	$ 15,076
U.S. treasury securities
Marketable securities:
Marketable securities	59,944
U.S. treasury securities \| Level 2
Marketable securities:
Marketable securities	59,944
U.S. government agency bonds
Marketable securities:
Marketable securities	11,989
U.S. government agency bonds \| Level 2
Marketable securities:
Marketable securities	11,989
Commercial paper
Marketable securities:
Marketable securities	44,862
Commercial paper \| Level 2
Marketable securities:
Marketable securities	44,862
Corporate debt securities
Marketable securities:
Marketable securities	12,600
Corporate debt securities \| Level 2
Marketable securities:
Marketable securities	$ 12,600

Accrued Expenses and Other Current Liabilities - Summary of Accrued expenses and other current liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accrued Expenses And Other Liabilities Current [Line Items]
Accrued employee compensation and benefits	$ 2,852	$ 3,255
Accrued external research and development expenses	1,304	1,344
Accrued professional fees	2,383	619
Deferred rent	1,373	1,370
Accrued property and equipment	786
Other	214	319
Total	$ 8,912	$ 6,907

Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended
	Jan. 09, 2020	Jun. 30, 2020
Temporary Equity [Line Items]
Shares issued during the period		19,936,296
Common Stock [Member]
Temporary Equity [Line Items]
Shares issued upon conversion		27,094,085
Series C Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Shares issued during the period	19,936,296
Shares issued price	$ 5.5914
Gross proceeds	$ 111,500
Stock issuance of costs	$ 2,600	$ 2,640

Equity - Additional Information (Detail) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Equity [Abstract]
Common stock, shares authorized	150,000,000	46,750,000
Common stock, par value per share	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	0
Preferred stock, par value per share	$ 0.0001	$ 0.0001

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		6 Months Ended
	Jun. 11, 2020	Jun. 30, 2020	Jan. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognised stock compensation on account of unvested options		$ 19.2
Unrecognised stock compensation on account of unvested options remaining period over which the compensation is to be recognised		3 years 1 month 6 days
Unvested Stock Awards for Which Performance is not Probable
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognised stock compensation on account of unvested options		$ 2.3
Service Based Options [Member] \| Certain Employees Directors and Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compenation by share based payment arrangement number of options granted		1,659,661
Share based compenation by share based payment arrangement number of options granted weighted average exercise price per share		$ 7.07
Period of vesting of employee stock options		4 years
Performance Based Options [Member] \| Certain Employees Directors and Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compenation by share based payment arrangement number of options granted		717,154
Share based compenation by share based payment arrangement number of options granted weighted average exercise price per share		$ 3.26
2020 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance	2,547,698
Stock based compensation vesting period service based		4 years
Stock based compensation period of expiry		10 years
Common stock shares available for future issuance		3,061,794
2020 Stock Incentive Plan \| Maximum \| Additional From 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance	7,173,014
2020 Stock Incentive Plan \| Maximum \| Annual Increase 2021 To 2030
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock shares additionally reserved for issuance	4.00%
Employee Stock Purchase Plan 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation by share based payment arrangement number of shares authorised for issuance	481,231
Common stock shares available for future issuance		481,231
Employee Stock Purchase Plan 2020 \| Maximum \| Annual Increase 2021 To 2030
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock shares additionally reserved for issuance	1.00%
Number of share instruments newly issued under a share-based compensation plan		1,302,157
Common Stock [Member] \| 2017 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation by share based payment arrangement number of shares authorised for issuance			10,275,717	8,407,405

Stock-Based Awards - Summary of Stock-Based Compensation Expense was Classified in the Statements of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 1,368	$ 1,049	$ 2,872	$ 2,042
Research and development expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	936	675	1,763	1,351
General and administrative expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 432	$ 374	$ 1,109	$ 691

Net Loss per Share - Summary of Potential Dilutive Securities, Presented Based on Amounts Outstanding (Detail) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	6,648,618	19,674,066
Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	0	14,961,027
Unvested restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	1,209,072	2,218,595
Stock option to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	5,439,546	2,494,444

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disclosure of Commitement and Contingencies [Line Items]
Lessee operating lease year of expiry			2029
Operating lease agreement option to renewal term	5 years		5 years
Tenant improvement allowance maximum	$ 14.7		$ 14.7
Letter of Credit for Security Deposit	2.1		2.1
Rent expense operating lease	$ 1.9	$ 1.3	$ 3.7	$ 3.5
Lease existence of option to extend			true

Commitments and Contingencies - Summary of Future Minimum Lease Payments (Detail) $ in Thousands	Jun. 30, 2020 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2020 (remaining 6 months)	$ 3,488
2021	7,053
2022	7,251
2023	7,441
2024	7,679
Thereafter	35,451
Future Monimum Lease Payments	$ 68,363