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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2020	Aug. 05, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Trading Symbol	AGLE
Security Exchange Name	NASDAQ
Entity Registrant Name	AEGLEA BIOTHERAPEUTICS, INC.
Entity Central Index Key	0001636282
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity File Number	001-37722
Entity Tax Identification Number	46-4312787
Entity Address, Address Line One	805 Las Cimas Parkway
Entity Address, Address Line Two	Suite 100
Entity Address, City or Town	Austin
Title of 12(b) Security	Common Stock, $0.0001 Par Value Per Share
Entity Address, Postal Zip Code	78746
City Area Code	512
Local Phone Number	942-2935
Entity Address, State or Province	TX
Entity Incorporation, State or Country Code	DE
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Ex Transition Period	true
Document Transition Report	false
Document Quarterly Report	true
Entity Common Stock, Shares Outstanding		44,599,847

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
CURRENT ASSETS
Cash and cash equivalents	$ 65,713	$ 19,253
Marketable securities	92,017	52,696
Prepaid expenses and other current assets	4,136	2,556
Total current assets	161,866	74,505
Restricted cash	1,500	1,500
Property and equipment, net	4,896	2,385
Operating lease right-of-use assets	4,557	4,726
Other non-current assets	92	67
TOTAL ASSETS	172,911	83,183
CURRENT LIABILITIES
Accounts payable	4,151	3,154
Operating lease liabilities	228	351
Accrued and other current liabilities	11,511	14,854
Total current liabilities	15,890	18,359
Non-current operating lease liabilities	4,695	4,712
Other non-current liabilities	68	31
TOTAL LIABILITIES	20,653	23,102
Commitments and Contingencies (Note 8)
STOCKHOLDERS’ EQUITY
Preferred stock, $0.0001 par value; 10,000,000 shares authorized as of June 30, 2020 and December 31, 2019; no shares issued and outstanding as of June 30, 2020 and December 31, 2019
Common stock, $0.0001 par value; 500,000,000 shares authorized as of June 30, 2020 and December 31, 2019; 44,599,847 shares and 29,084,437 shares issued and outstanding as of June 30, 2020 and December 31, 2019, respectively	5	3
Additional paid-in capital	387,475	255,142
Accumulated other comprehensive income	39	51
Accumulated deficit	(235,261)	(195,115)
TOTAL STOCKHOLDERS’ EQUITY	152,258	60,081
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 172,911	$ 83,183

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Type of revenue [extensible list]	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses:
Research and development	$ 16,869	$ 14,806	$ 31,431	$ 29,195
General and administrative	4,691	3,816	9,151	7,084
Total operating expenses	21,560	18,622	40,582	36,279
Loss from operations	(21,560)	(18,622)	(40,582)	(36,279)
Other income (expense):
Interest income	161	619	461	1,126
Other expense, net	(19)	(16)	(25)	(33)
Total other income	142	603	436	1,093
Net loss	$ (21,418)	$ (18,019)	$ (40,146)	$ (35,186)
Net loss per share, basic and diluted	$ (0.40)	$ (0.55)	$ (0.93)	$ (1.14)
Weighted-average common shares outstanding, basic and diluted	52,941,603	32,840,357	43,019,670	30,936,623

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (21,418)	$ (18,019)	$ (40,146)	$ (35,186)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities	173	54	(12)	94
Total comprehensive loss	$ (21,245)	$ (17,965)	$ (40,158)	$ (35,092)

- Definition

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

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+ Details

Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balances at Dec. 31, 2018	$ 67,428	$ 2	$ 184,314	$ (27)	$ (116,861)
Balances (in shares) at Dec. 31, 2018		24,140
Issuance of common stock in connection with employee stock purchase plan	143		143
Issuance of common stock in connection with employee stock purchase plan (in shares)		20
Issuance of common stock in connection with exercise of stock options	261		261
Issuance of common stock in connection with exercise of stock options (in shares)		52
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs	64,503	$ 1	64,502
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs (in shares)		4,625
Stock-based compensation expense	1,081		1,081
Unrealized gain (loss) on marketable securities	40			40
Net loss	(17,167)				(17,167)
Balances at Mar. 31, 2019	116,289	$ 3	250,301	13	(134,028)
Balances (in shares) at Mar. 31, 2019		28,837
Balances at Dec. 31, 2018	67,428	$ 2	184,314	(27)	(116,861)
Balances (in shares) at Dec. 31, 2018		24,140
Unrealized gain (loss) on marketable securities	94
Net loss	(35,186)
Balances at Jun. 30, 2019	99,615	$ 3	251,592	67	(152,047)
Balances (in shares) at Jun. 30, 2019		28,848
Balances at Mar. 31, 2019	116,289	$ 3	250,301	13	(134,028)
Balances (in shares) at Mar. 31, 2019		28,837
Issuance of common stock in connection with exercise of stock options	46		46
Issuance of common stock in connection with exercise of stock options (in shares)		11
Stock-based compensation expense	1,245		1,245
Unrealized gain (loss) on marketable securities	54			54
Net loss	(18,019)				(18,019)
Balances at Jun. 30, 2019	99,615	$ 3	251,592	67	(152,047)
Balances (in shares) at Jun. 30, 2019		28,848
Balances at Dec. 31, 2019	60,081	$ 3	255,142	51	(195,115)
Balances (in shares) at Dec. 31, 2019		29,084
Issuance of common stock in connection with employee stock purchase plan	174		174
Issuance of common stock in connection with employee stock purchase plan (in shares)		26
Issuance of common stock in connection with exercise of stock options	115		115
Issuance of common stock in connection with exercise of stock options (in shares)		37
Stock-based compensation expense	1,348		1,348
Unrealized gain (loss) on marketable securities	(185)			(185)
Net loss	(18,728)				(18,728)
Balances at Mar. 31, 2020	42,805	$ 3	256,779	(134)	(213,843)
Balances (in shares) at Mar. 31, 2020		29,147
Balances at Dec. 31, 2019	60,081	$ 3	255,142	51	(195,115)
Balances (in shares) at Dec. 31, 2019		29,084
Unrealized gain (loss) on marketable securities	(12)
Net loss	(40,146)
Balances at Jun. 30, 2020	152,258	$ 5	387,475	39	(235,261)
Balances (in shares) at Jun. 30, 2020		44,600
Balances at Mar. 31, 2020	42,805	$ 3	256,779	(134)	(213,843)
Balances (in shares) at Mar. 31, 2020		29,147
Issuance of common stock in connection with exercise of stock options	44		44
Issuance of common stock in connection with exercise of stock options (in shares)		10
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs	129,054	$ 2	129,052
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs (in shares)		15,443
Stock-based compensation expense	1,600		1,600
Unrealized gain (loss) on marketable securities	173			173
Net loss	(21,418)				(21,418)
Balances at Jun. 30, 2020	$ 152,258	$ 5	$ 387,475	$ 39	$ (235,261)
Balances (in shares) at Jun. 30, 2020		44,600

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (40,146)	$ (35,186)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	376	207
Purchase net discount on marketable securities	19	480
Net accretion of discount on marketable securities	(58)	(543)
Stock-based compensation	2,948	2,326
Non-cash operating lease expense	306	191
Other	(15)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,637)	(2,223)
Accounts payable	1,318	2,141
Operating lease liabilities	(277)	(178)
Accrued and other liabilities	(3,941)	595
Net cash used in operating activities	(41,107)	(32,190)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(2,714)	(175)
Purchases of marketable securities	(75,500)	(77,956)
Proceeds from maturities of marketable securities	36,206	50,054
Net cash used in investing activities	(42,008)	(28,077)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of common stock and pre-funded warrants in public offering, net of offering costs	129,250	64,298
Proceeds from employee stock plan purchases and stock option exercises	333	450
Principal payments on finance lease obligation	(8)	(12)
Net cash provided by financing activities	129,575	64,736
NET INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	46,460	4,469
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH
Beginning of period	20,753	22,461
End of period	67,213	26,930
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Leased assets obtained in exchange for lease obligations	176	$ 5,294
Unpaid amounts related to purchase of property and equipment	$ 440

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Such management estimates include those related to accruals of research and development related costs, stock-based compensation, and certain company income tax related items. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ significantly from those estimates.

Cash and Cash Equivalents

The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents consist of money market funds and debt securities and are stated at fair value.

Marketable Securities

All investments have been classified as available-for-sale and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its investments in debt securities at the time of purchase. The Company may or may not hold securities with stated maturities greater than one year until maturity. All available-for-sale securities are considered available to support current operations and are classified as current assets. The Company presents credit losses as an allowance rather than as a reduction in the amortized cost of the available-for-sale securities.

For available-for-sale debt securities in an unrealized loss position, the Company first assesses whether it intends to sell, or it is more likely than not that it will be required to sell the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value and recognized in other income (expense) in the results of operations. For available-for-sale debt securities that do not meet the aforementioned criteria, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, management considers the extent to which fair value is less than amortized cost, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, an allowance is recorded for the difference between the present value of cash flows expected to be collected and the amortized cost basis of the security. Impairment losses attributable to credit loss factors are charged against the allowance when management believes an available-for-sale security is uncollectible or when either of the criteria regarding intent or requirement to sell is met.

Any unrealized losses from declines in fair value below the amortized cost basis as a result of non-credit loss factors is recognized as a component of accumulated other comprehensive (loss) income, along with unrealized gains. Realized gains and losses and declines in fair value, if any, on available-for-sale securities are included in other income (expense) in the results of operations. The cost of securities sold is based on the specific-identification method.

Restricted Cash

Restricted cash consists of a money market account held by a financial institution as collateral for the Company’s obligations under its facility lease for the Company’s corporate headquarters in Austin, TX.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, marketable securities, and restricted cash. The Company’s investment policy limits investments to high credit quality securities issued by the U.S. government, U.S. government-sponsored agencies, highly rated banks, and corporate issuers, subject to certain concentration limits and restrictions on maturities. The Company’s cash, cash equivalents, marketable securities, and restricted cash are held by financial institutions in the United States that management believes are of high credit quality. Amounts on deposit may at times exceed federally insured limits. The Company has not experienced any losses on its deposits of cash, cash equivalents, and restricted cash and its accounts are monitored by management to mitigate risk. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash, cash equivalents, restricted cash, and bond issuers.

Property and Equipment

Property and equipment are stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets. Repairs and maintenance that do not extend the life or improve an asset are expensed as incurred. Upon retirement or sale, the cost of disposed assets and their related accumulated depreciation and amortization are removed from the balance sheet. Any gain or loss is credited or charged to operations.

The useful lives of the property and equipment are as follows:

Laboratory equipment		5 years
Furniture and office equipment		5 years
Computer equipment		3 years
Software		3 years
Leasehold improvements		Shorter of remaining lease term or estimated useful life

Impairment of Long-Lived Assets

Long-lived assets are reviewed for indications of possible impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amounts to the future undiscounted cash flows attributable to these assets. An impairment loss is recognized to the extent an asset group is not recoverable, and the carrying amount exceeds the projected discounted future cash flows arising from these assets. There were no impairments of long-lived assets for the six months ended June 30, 2020 and 2019.

Accrued Research and Development Costs

The Company records the costs associated with research, nonclinical studies, clinical trials, and manufacturing development as incurred. These costs are a significant component of the Company’s research and development expenses, with a substantial portion of the Company’s on-going research and development activities conducted by third-party service providers, including contract research and manufacturing organizations.

The Company accrues for expenses resulting from obligations under agreements with contract research organizations (“CROs”), contract manufacturing organizations (“CMOs”), and other outside service providers for which payment flows do not match the periods over which materials or services are provided to the Company. Accruals are recorded based on estimates of services received and efforts expended pursuant to agreements established with CROs, CMOs, and other outside service providers. These estimates are typically based on contracted amounts applied to the proportion of work performed and determined through analysis with internal personnel and external service providers as to the progress or stage of completion of the services. The Company makes significant judgments and estimates in determining the accrual balance in each reporting period. In the event advance payments are made to a CRO, CMO, or outside service provider, the payments will be recorded as a prepaid asset which will be amortized as the contracted services are performed. As actual costs become known, the Company adjusts its accruals. Inputs, such as the services performed, the number of patients enrolled, or the study duration, may vary from the Company’s estimates, resulting in adjustments to research and development expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. Historically, the Company has not experienced any material deviations between accrued and actual research and development expenses.

Leases

The Company determines if an arrangement is a lease at inception. Right-of-use ("ROU") 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. The classification of the Company's leases as operating or finance leases along with the initial measurement and recognition of the associated ROU assets and lease liabilities is performed at the lease commencement date. The measurement of lease liabilities is based on the present value of future lease payments over the lease term. As the Company's leases do not provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of future lease payments. The ROU asset is based on the measurement of the lease liability and also includes any lease payments made prior to or on lease commencement and excludes lease incentives and initial direct costs incurred, as applicable. The lease terms may include options to extend or terminate the lease when it is reasonably certain the Company will exercise any such options. Rent expense for the Company's operating leases is recognized on a straight-line basis over the lease term. Amortization expense for the ROU asset associated with its finance leases is recognized on a straight-line basis over the term of the lease and interest expense associated with its finance leases is recognized on the balance of the lease liability using the effective interest method based on the estimated incremental borrowing rate.

The Company has lease agreements with lease and non-lease components. As allowed under Topic 842, the Company has elected to not separate lease and non-lease components for any leases involving real estate and office equipment classes of assets and, as a result, accounts for the lease and non-lease components as a single lease component. The Company has also elected to not apply the recognition requirement of Topic 842 to leases with a term of 12 months or less for all classes of assets.

Fair Value of Financial Instruments

The Company uses fair value measurements to record fair value adjustments to certain financial and non-financial assets and liabilities and to determine fair value disclosures. The accounting standards define fair value, establish a framework for measuring fair value, and require disclosures about fair value measurements. Fair value is defined as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities required to be recorded at fair value, the principal or most advantageous market in which the Company would transact are considered

along with assumptions that market participants would use when pricing the asset or liability, such as inherent risk, transfer restrictions, and risk of nonperformance.

The accounting standard for fair value establishes a fair value hierarchy based on three levels of inputs, the first two of which are considered observable and the last unobservable, that requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. A financial instrument’s categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement.

The three levels of inputs that may be used to measure fair value are as follows:

Level 1:

Observable inputs, such as quoted prices in active markets for identical assets or liabilities.

Level 2:

Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3:

Valuations based on unobservable inputs to the valuation methodology and including data about assumptions that market participants would use in pricing the asset or liability based on the best information available under the circumstances.

Financial instruments carried at fair value include cash, cash equivalents, marketable securities, and restricted cash. The carrying amount of accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development costs include, but are not limited to, salaries, benefits, travel, stock-based compensation, consulting costs, contract research service costs, laboratory supplies and facilities, contract manufacturing costs, and costs paid to other third parties that conduct research and development activities on the Company’s behalf. Amounts incurred in connection with license agreements are also included in research and development expense.

Advance payments for goods or services to be rendered in the future for use in research and development activities are recorded as a prepaid asset and expensed as the related goods are delivered or the services are performed.

Stock-Based Compensation

The Company recognizes the cost of stock-based awards granted to employees and non-employees based on the estimated grant-date fair values of the awards. The value of the award is recognized as compensation expense on a straight-line basis over the requisite service period. Forfeitures are recognized when they occur, which may result in the reversal of compensation costs in subsequent periods as the forfeitures arise. Compensation expense for employee and non-employee share-based payment awards with performance conditions is recognized when the performance condition is deemed probable.

Income Taxes

The Company and its eight wholly owned subsidiary corporations use the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequences of temporary differences between the financial statements and the tax bases of assets and liabilities. Additionally, any changes in income tax laws are immediately recognized in the quarter of enactment.

A valuation allowance is established against the deferred tax assets to reduce their carrying value to an amount that is more likely than not to be realized. The deferred tax assets and liabilities are classified as noncurrent along with the related valuation allowance. Due to a lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance.

The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on the technical merits, as the largest amount of benefits that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the unrecognized tax benefits as a component of income tax expense, if applicable.

On March 27, 2020, the Coronavirus Aid, Relief and Economic Security (“CARES”) Act was enacted and signed into law in response to COVID-19. The CARES Act includes changes to the tax provisions that benefit business entities and makes certain technical corrections to the 2017 Tax Cuts and Jobs Act. The tax relief measures for businesses include a five-year net operating loss carryback, suspension of annual deduction limitation of 80% of taxable income from net operating losses generated in a tax year beginning after December 31, 2017, changes in the deductibility of interest, acceleration of alternative minimum tax credit refunds, payroll tax relief, technical corrections on net operating loss carryforwards for fiscal year taxpayers and allowing accelerated deductions for qualified improvement property. The CARES Act also provides other non-tax benefits to assist those impacted by the pandemic. The Company evaluated the impact and determined the CARES Act did not have a material impact on its consolidated financial condition or results of operations as of and for the six months ended June 30, 2020.

Comprehensive Loss

Comprehensive loss is the change in stockholders’ equity from transactions and other events and circumstances other than those resulting from investments by stockholders and distributions to stockholders. The Company’s other comprehensive income is currently comprised of changes in unrealized losses and gains on available-for-sale securities.

Recently Adopted Accounting Pronouncements

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which changes the impairment model for most financial assets and certain other instruments. For available-for-sale debt securities with unrealized credit losses, the credit losses will be recognized as allowances rather than as reductions in the amortized cost of the securities. On January 1, 2020, the Company adopted ASU 2016-13 using the modified retrospective approach and no cumulative effect adjustment to accumulated deficit was needed as of the adoption date. Additionally, no prior period amounts were adjusted and continue to be reported in accordance with the legacy other-than-temporary impairment model. The adoption of ASU 2016-13 did not have a material impact on the Company’s consolidated financial statements.

In August 2018, the FASB issued ASU No. 2018-15, Intangibles – Goodwill and Other – Internal Use Software (Subtopic 350-40), to align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The amendments in the update require an entity in a hosting arrangement that is a service contract to follow the guidance in Subtopic 350-40 to determine which implementation costs to capitalize as an asset related to the service contract and which costs to expense. Capitalized implementation costs are recorded in prepaid expenses and other current assets or other non-current assets on the statement of financial position and the related amortization expense is recorded in operating expenses in the results of operations. On January 1, 2020, the Company adopted ASU 2018-15 on a prospective basis and no prior period amounts were adjusted. The adoption of ASU 2018-15 did not have a material impact on the Company’s consolidated financial statements.

Fair Value Measurements

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The Company measures and reports certain financial instruments as assets and liabilities at fair value on a recurring basis. The following tables sets forth the fair value of the Company’s financial assets and liabilities at fair value on a recurring basis based on the three-tier fair value hierarchy (in thousands):

	June 30, 2020
	Level 1		Level 2		Level 3		Total
Financial Assets
Money market funds	$	43,306	$	—	$	—	$	43,306
U.S. treasury securities		—		71,464		—		71,464
U.S. government agency securities		—		10,534		—		10,534
Commercial paper		—		1,751		—		1,751
Corporate bonds		—		18,766		—		18,766
Total financial assets	$	43,306	$	102,515	$	—	$	145,821

	December 31, 2019
	Level 1		Level 2		Level 3		Total
Financial Assets
Money market funds	$	7,023	$	—	$	—	$	7,023
Reverse repurchase agreements		—		6,250		—		6,250
Commercial paper		—		15,193		—		15,193
Corporate bonds		—		39,750		—		39,750
Total financial assets	$	7,023	$	61,193	$	—	$	68,216

The Company measures the fair value of money market funds on quoted prices in active markets for identical asset or liabilities. The Level 2 assets include U.S. treasury securities, U.S. government agency securities, reverse repurchase agreements, commercial paper, and corporate bonds and are valued based on quoted prices for similar assets in active markets and inputs other than quoted prices that are derived from observable market data.

The Company evaluates transfers between levels at the end of each reporting period. There were no transfers between Level 1 and Level 2 during the periods presented.

- 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

Cash Equivalents and Marketable Securities

6 Months Ended

Jun. 30, 2020

Investments Debt And Equity Securities [Abstract]

Cash Equivalents and Marketable Securities

4. Cash Equivalents and Marketable Securities

The following tables summarize the estimated fair value of the Company’s cash equivalents and marketable securities and the gross unrealized gains and losses (in thousands):

	June 30, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash equivalents
Money market funds	$	43,306	$	—	$	—		$	43,306
U.S. treasury securities		5,499		—		—			5,499
U.S. government agency securities		4,999		—		—			4,999
Total cash equivalents		53,804		—		—			53,804

Marketable securities
U.S. treasury securities		65,966		3		(4	)		65,965
U.S. government agency securities		5,535		—		—			5,535
Commercial paper		1,748		3		—			1,751
Corporate bonds		18,729		38		(1	)		18,766
Total marketable securities	$	91,978	$	44	$	(5	)	$	92,017

	December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash equivalents
Money market funds	$	7,023	$	—	$	—		$	7,023
Reverse repurchase agreements		6,250		—		—			6,250
Commercial paper		2,247		—		—			2,247
Total cash equivalents		15,520		—		—			15,520

Marketable securities
Commercial paper		12,931		15		—			12,946
Corporate bonds		39,714		45		(9	)		39,750
Total marketable securities	$	52,645	$	60	$	(9	)	$	52,696

The reverse repurchase agreements are settled in cash nightly, and as such are classified as cash equivalents.

The following table summarizes available-for-sale securities in an unrealized loss position for which an allowance for credit losses has not been recorded at June 30, 2020 and December 31, 2019, aggregated by major security type and length of time in a continuous unrealized loss position:

	June 30, 2020
	Less Than 12 Months					12 Months or Longer				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
U.S. treasury securities	$	24,987	$	(4	)	$	—	$	—	$	24,987	$	(4	)
Corporate bonds		5,001		(1	)		—		—		5,001		(1	)
Total	$	29,988	$	(5	)	$	—	$	—	$	29,988	$	(5	)

	December 31, 2019
	Less Than 12 Months					12 Months or Longer				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Corporate bonds	$	13,022	$	(9	)	$	—	$	—	$	13,022	$	(9	)

As of June 30, 2020 and December 31, 2019, the Company held 11 and 13 debt securities, respectively, that were in an unrealized loss position. The Company evaluated its securities for credit losses and considered the decline in market value to be primarily attributable to current economic and market conditions and not attributable to a credit loss or other factors. Additionally, the Company does not intend to sell the securities in an unrealized loss position and does not expect they will be required to sell the securities before recovery of the unamortized cost basis. As of June 30, 2020 and December 31, 2019, an allowance for credit losses had not been recognized and no marketable securities were considered impaired.

There were no realized gains or losses on marketable securities for the six months ended June 30, 2020 and 2019. Interest on marketable securities is included in interest income. Accrued interest receivable on available-for-sale debt securities totaled $0.1 million and $0.3 million at June 30, 2020 and December 31, 2019, respectively, and is excluded from the estimate of credit losses.

The following table summarizes the contractual maturities of the Company’s marketable securities at estimated fair value (in thousands):

	June 30,		December 31,
	2020		2019
Due in one year or less	$	92,017	$	49,687
Due in 1 - 2 years		—		3,009
Total marketable securities	$	92,017	$	52,696

The Company may sell investments at any time for use in current operations even if they have not yet reached maturity. As a result, the Company classifies marketable securities, including securities with maturities beyond twelve months as current assets.

Stockholders' Equity

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stockholders' Equity

6. Stockholders’ Equity

Public Offering

In April 2020, the Company issued and sold 15,442,303 shares of common stock at a public offering price of $4.75 per share and pre-funded warrants to purchase up to 13,610,328 shares of common stock at a public offering price of $4.7499 per warrant in an underwritten public offering pursuant to a shelf registration statement on Form S-3. This includes the full exercise by the underwriters of their option to purchase up to 3,789,473 additional shares of common stock. The net proceeds to the Company from this public offering were approximately $129.1 million, after deducting underwriting discounts and commissions of $8.2 million and offering costs of $0.7 million.

The public offering price for the pre-funded warrants was equal to the public offering price of the common stock, less the $0.0001 per share exercise price of each warrant. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital and have no expiration date. Per the terms of the warrant agreement, the outstanding warrants to purchase shares of common stock may not be exercised if the holder’s ownership of the Company’s common stock would exceed 4.99% (“Maximum Ownership Percentage”). By written notice to the Company, the holders may increase or decrease the Maximum Ownership Percentage up to 19.99%. The revised Maximum Ownership Percentage would be effective 60 days after the notice is received by the Company.

As of June 30, 2020, the following pre-funded warrants for common stock were issued and outstanding:

Issue Date	Expiration Date	Exercise Price		Number of Warrants Outstanding
February 8, 2019	None	$	0.0001		4,000,000
April 30, 2020	None	$	0.0001		13,610,328
Total pre-funded warrants					17,610,328

Stock-Based Compensation

The 2016 Equity Incentive Plan (“2016 Plan”) provides for an automatic increase in the number of shares reserved for issuance thereunder on January 1 of each year for the remaining term of the plan (through 2028) equal to (a) 4.0% of the number of issued and outstanding shares of common stock on December 31 of the immediately preceding year, or (b) a lesser amount as approved by the Company’s board of directors each year. As a result of this provision, on January 1, 2020 and January 1, 2019, an additional 1,163,377 and 965,603 shares, respectively, became available for issuance under the 2016 Plan.

As of June 30, 2020, the 2016 Plan had 1,341,292 shares available for future issuance.

During the three months ended June 30, 2020 and 2019, the Company issued an aggregate of 239,400 and 159,600 options to purchase common stock, respectively, under the Company’s equity incentive plans for an aggregate fair value of $1.2 million and $0.7 million, respectively.

During the six months ended June 30, 2020 and 2019, the Company issued an aggregate of 1,444,400 and 1,201,900 options to purchase common stock, respectively, under the Company’s equity incentive plans for an aggregate fair value of $7.6 million and $6.9 million, respectively.

There were no shares issued and sold under the Company’s 2016 Employee Stock Purchase Plan (“2016 ESPP”) during the three months ended June 30, 2020 and 2019. The Company issued and sold 25,928 shares for aggregate cash proceeds of $0.2 million during the six months ended June 30, 2020 and 20,132 shares for aggregate cash proceeds of $0.1 million during the six months ended June 30, 2019.

Total stock-based compensation expense related to the Company’s equity incentive plans and 2016 ESPP was as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
Research and development	$	665	$	464	$	1,197	$	866
General and administrative		935		781		1,751		1,460
Total stock-based compensation expense	$	1,600	$	1,245	$	2,948	$	2,326

The following table summarizes the weighted-average Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted under the Company’s equity incentive plans, and the shares purchasable under the 2016 ESPP during the periods presented:

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2020			2019			2020			2019
Equity Incentive Plans
Expected term (in years)		5.50			5.70			5.94			5.99
Expected volatility		77	%		78	%		75	%		81	%
Risk-free interest		0.46	%		2.05	%		1.29	%		2.50	%
Dividend yield		0	%		0	%		0	%		0	%

2016 ESPP
Expected term (in years)		—			—			0.50			0.49
Expected volatility		—			—			53	%		66	%
Risk-free interest		—			—			1.49	%		2.55	%
Dividend yield		—			—			0	%		0	%

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2020

Accounting Policies [Abstract]

Use of Estimates

Cash and Cash Equivalents

Marketable Securities

Restricted Cash

Concentration of Credit Risk

Property and Equipment

The useful lives of the property and equipment are as follows:

Laboratory equipment		5 years
Furniture and office equipment		5 years
Computer equipment		3 years
Software		3 years
Leasehold improvements		Shorter of remaining lease term or estimated useful life

Impairment of Long-Lived Assets

Accrued Research And Development Costs

Accrued Research and Development Costs

Leases

Fair Value of Financial Instruments

along with assumptions that market participants would use when pricing the asset or liability, such as inherent risk, transfer restrictions, and risk of nonperformance.

The three levels of inputs that may be used to measure fair value are as follows:

Level 1:

Observable inputs, such as quoted prices in active markets for identical assets or liabilities.

Level 2:

Level 3:

Research and Development Costs

Stock-Based Compensation

Income Taxes

Comprehensive Income

Comprehensive Loss

Recent Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Fair Value Measurement (Tables)

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

Financial Assets and Liabilities Measured at Fair Value on Recurring Basis

The following tables sets forth the fair value of the Company’s financial assets and liabilities at fair value on a recurring basis based on the three-tier fair value hierarchy (in thousands):

	June 30, 2020
	Level 1		Level 2		Level 3		Total
Financial Assets
Money market funds	$	43,306	$	—	$	—	$	43,306
U.S. treasury securities		—		71,464		—		71,464
U.S. government agency securities		—		10,534		—		10,534
Commercial paper		—		1,751		—		1,751
Corporate bonds		—		18,766		—		18,766
Total financial assets	$	43,306	$	102,515	$	—	$	145,821

	December 31, 2019
	Level 1		Level 2		Level 3		Total
Financial Assets
Money market funds	$	7,023	$	—	$	—	$	7,023
Reverse repurchase agreements		—		6,250		—		6,250
Commercial paper		—		15,193		—		15,193
Corporate bonds		—		39,750		—		39,750
Total financial assets	$	7,023	$	61,193	$	—	$	68,216

Cash Equivalents and Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2020

Investments Debt And Equity Securities [Abstract]

Schedule of Estimated Fair Value of Cash Equivalents and Marketable Securities

The following tables summarize the estimated fair value of the Company’s cash equivalents and marketable securities and the gross unrealized gains and losses (in thousands):

	June 30, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash equivalents
Money market funds	$	43,306	$	—	$	—		$	43,306
U.S. treasury securities		5,499		—		—			5,499
U.S. government agency securities		4,999		—		—			4,999
Total cash equivalents		53,804		—		—			53,804

Marketable securities
U.S. treasury securities		65,966		3		(4	)		65,965
U.S. government agency securities		5,535		—		—			5,535
Commercial paper		1,748		3		—			1,751
Corporate bonds		18,729		38		(1	)		18,766
Total marketable securities	$	91,978	$	44	$	(5	)	$	92,017

	December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash equivalents
Money market funds	$	7,023	$	—	$	—		$	7,023
Reverse repurchase agreements		6,250		—		—			6,250
Commercial paper		2,247		—		—			2,247
Total cash equivalents		15,520		—		—			15,520

Marketable securities
Commercial paper		12,931		15		—			12,946
Corporate bonds		39,714		45		(9	)		39,750
Total marketable securities	$	52,645	$	60	$	(9	)	$	52,696

Schedule of Gross Unrealized Losses and Fair Value by Investment Category and Age

	June 30, 2020
	Less Than 12 Months					12 Months or Longer				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
U.S. treasury securities	$	24,987	$	(4	)	$	—	$	—	$	24,987	$	(4	)
Corporate bonds		5,001		(1	)		—		—		5,001		(1	)
Total	$	29,988	$	(5	)	$	—	$	—	$	29,988	$	(5	)

	December 31, 2019
	Less Than 12 Months					12 Months or Longer				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Corporate bonds	$	13,022	$	(9	)	$	—	$	—	$	13,022	$	(9	)

Summary of Contractual Maturities of Marketable Securities at Estimated Fair Value

The following table summarizes the contractual maturities of the Company’s marketable securities at estimated fair value (in thousands):

	June 30,		December 31,
	2020		2019
Due in one year or less	$	92,017	$	49,687
Due in 1 - 2 years		—		3,009
Total marketable securities	$	92,017	$	52,696

Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary Of Pre-funded Warrants For Common Stock Issued And Outstanding

As of June 30, 2020, the following pre-funded warrants for common stock were issued and outstanding:

Issue Date	Expiration Date	Exercise Price		Number of Warrants Outstanding
February 8, 2019	None	$	0.0001		4,000,000
April 30, 2020	None	$	0.0001		13,610,328
Total pre-funded warrants					17,610,328

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense related to the Company’s equity incentive plans and 2016 ESPP was as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
Research and development	$	665	$	464	$	1,197	$	866
General and administrative		935		781		1,751		1,460
Total stock-based compensation expense	$	1,600	$	1,245	$	2,948	$	2,326

Schedule of Estimated Fair Value of Stock Options Granted

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2020			2019			2020			2019
Equity Incentive Plans
Expected term (in years)		5.50			5.70			5.94			5.99
Expected volatility		77	%		78	%		75	%		81	%
Risk-free interest		0.46	%		2.05	%		1.29	%		2.50	%
Dividend yield		0	%		0	%		0	%		0	%

2016 ESPP
Expected term (in years)		—			—			0.50			0.49
Expected volatility		—			—			53	%		66	%
Risk-free interest		—			—			1.49	%		2.55	%
Dividend yield		—			—			0	%		0	%

Cash Equivalents and Marketable Securities - Schedule of Estimated Fair Value of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	$ 53,804	$ 15,520
Cash equivalents, estimated fair value	53,804	15,520
Marketable securities, amortized cost	91,978	52,645
Marketable securities, gross unrealized gains	44	60
Marketable securities, gross unrealized losses	(5)	(9)
Marketable securities, estimated fair value	92,017	52,696
Money market funds
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	43,306	7,023
Cash equivalents, estimated fair value	43,306	7,023
U.S. treasury securities
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	5,499
Cash equivalents, estimated fair value	5,499
Marketable securities, amortized cost	65,966
Marketable securities, gross unrealized gains	3
Marketable securities, gross unrealized losses	(4)
Marketable securities, estimated fair value	65,965
U.S. government agency securities
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost	4,999
Cash equivalents, estimated fair value	4,999
Marketable securities, amortized cost	5,535
Marketable securities, estimated fair value	5,535
Reverse repurchase agreements
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost		6,250
Cash equivalents, estimated fair value		6,250
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, amortized cost		2,247
Cash equivalents, estimated fair value		2,247
Marketable securities, amortized cost	1,748	12,931
Marketable securities, gross unrealized gains	3	15
Marketable securities, estimated fair value	1,751	12,946
Corporate bonds
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, amortized cost	18,729	39,714
Marketable securities, gross unrealized gains	38	45
Marketable securities, gross unrealized losses	(1)	(9)
Marketable securities, estimated fair value	$ 18,766	$ 39,750

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued	15,442,303	44,599,847		44,599,847			29,084,437
Public offering price of common stock	$ 4.75
Additional commons stock shares issued	3,789,473
Proceeds from issue of common stock	$ 129.1
Underwriter's discount and commission	8.2
Offering cost	$ 0.7
Reduction in exercise price of each warrant from public offering price for pre-funded warrants per share	$ 0.0001
Maximum ownership percentage for outstanding warrants to purchase shares of common stock to be exercised	4.99%
Period after notice received by company maximum ownership percentage to be effective description				The revised Maximum Ownership Percentage would be effective 60 days after the notice is received by the Company.
2016 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of outstanding share of common stock				4.00%
Additional number of shares available for issuance						1,163,377		965,603
Common stock available for future issuance		1,341,292		1,341,292
2016 Equity Incentive Plan \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option to purchase an aggregate of common stock shares		239,400	159,600	1,444,400	1,201,900
Stock options to purchase common stock aggregate fair value		$ 1.2	$ 0.7	$ 7.6	$ 6.9
2016 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option to purchase an aggregate of common stock shares		0	0	25,928	20,132
Aggregate cash proceeds from sale of shares				$ 0.2	$ 0.1
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum ownership percentage for outstanding warrants to purchase shares of common stock to be exercised	19.99%
Pre Funded Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued	13,610,328
Public offering price of common stock	$ 4.7499

The Company and Basis of Presentation - Additional Information (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segments \| Segment	1
Working capital	$ 146,000
Accumulated deficit	(235,261)	$ (195,115)
Cash, cash equivalents, marketable securities, and restricted cash	$ 159,200

Summary of Significant Accounting Policies - Additional Information (Details)		6 Months Ended
	Mar. 27, 2020	Jun. 30, 2020 USD ($) Subsidary	Jun. 30, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Impairments of long-lived assets \| $		$ 0	$ 0
Number of subsidiary corporations owned \| Subsidary		8
Net operating loss carryback period	5 years
Net operating loss carryforwards taxable income suspension of annual deduction limitation Percentage	80.00%
Maximum
Summary Of Significant Accounting Policies [Line Items]
Marketable securities stated maturity period		1 year

Summary of Significant Accounting Policies - Summary of Useful Lives of Property and Equipment (Details)	6 Months Ended
	Jun. 30, 2020
Laboratory Equipment
Property Plant And Equipment [Line Items]
Useful lives of the property and equipment	5 years
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Useful lives of the property and equipment	5 years
Computer Equipment
Property Plant And Equipment [Line Items]
Useful lives of the property and equipment	3 years
Software
Property Plant And Equipment [Line Items]
Useful lives of the property and equipment	3 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Useful lives of the property and equipment	Shorter of remaining lease term or estimated useful life

Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financial Assets
Financial assets, fair value	$ 145,821	$ 68,216
Money market funds
Financial Assets
Financial assets, fair value	43,306	7,023
U.S. treasury securities
Financial Assets
Financial assets, fair value	71,464
U.S. government agency securities
Financial Assets
Financial assets, fair value	10,534
Reverse repurchase agreements
Financial Assets
Financial assets, fair value		6,250
Commercial paper
Financial Assets
Financial assets, fair value	1,751	15,193
Corporate bonds
Financial Assets
Financial assets, fair value	18,766	39,750
Level 1
Financial Assets
Financial assets, fair value	43,306	7,023
Level 1 \| Money market funds
Financial Assets
Financial assets, fair value	43,306	7,023
Level 2
Financial Assets
Financial assets, fair value	102,515	61,193
Level 2 \| U.S. treasury securities
Financial Assets
Financial assets, fair value	71,464
Level 2 \| U.S. government agency securities
Financial Assets
Financial assets, fair value	10,534
Level 2 \| Reverse repurchase agreements
Financial Assets
Financial assets, fair value		6,250
Level 2 \| Commercial paper
Financial Assets
Financial assets, fair value	1,751	15,193
Level 2 \| Corporate bonds
Financial Assets
Financial assets, fair value	$ 18,766	$ 39,750

Fair Value Measurements - Additional Information (Details)	Jun. 30, 2020 USD ($)
Fair Value Disclosures [Abstract]
Fair value assets transferred from level 1 to level 2	$ 0

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	44,599,847	29,084,437
Common stock, shares outstanding	44,599,847	29,084,437

Cash Equivalents and Marketable Securities - Schedule of Gross Unrealized Losses and Fair Value by Investment Category and Age (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 29,988
Less than 12 Months, Unrealized Loss	(5)
Total, Fair Value	29,988
Total, Unrealized Loss	(5)
U.S. treasury securities
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	24,987
Less than 12 Months, Unrealized Loss	(4)
Total, Fair Value	24,987
Total, Unrealized Loss	(4)
Corporate bonds
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	5,001	$ 13,022
Less than 12 Months, Unrealized Loss	(1)	(9)
Total, Fair Value	5,001	13,022
Total, Unrealized Loss	$ (1)	$ (9)

Cash Equivalents and Marketable Securities - Additional Information (Details) - US Government Agencies Debt Securities $ in Thousands			6 Months Ended
	Jun. 30, 2020 USD ($) Security	Dec. 31, 2019 USD ($) Security	Jun. 30, 2020 USD ($) Security	Jun. 30, 2019 USD ($)
Cash Equivalents And Marketable Securities [Line Items]
Number of debt securities held \| Security	11	13	11
Allowance for Credit Loss	$ 0	$ 0	$ 0
Impairment of marketable securities	0	0
Realized gains or losses on marketable securities			0	$ 0
Accrued interest receivable on available-for-sale debt securities	$ 100	$ 300	$ 100

Cash Equivalents and Marketable Securities - Summary of Contractual Maturities of Marketable Securities at Estimated Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Due in one year or less	$ 92,017	$ 49,687
Due in 1 - 2 years		3,009
Total marketable securities	$ 92,017	$ 52,696

Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accrued Liabilities And Other Liabilities [Abstract]
Accrued compensation	$ 2,208	$ 3,273
Accrued contracted research and development costs	7,927	10,485
Accrued professional and consulting fees	769	627
Other	607	469
Total accrued and other current liabilities	$ 11,511	$ 14,854

Stockholders' Equity - Summary Of Pre-funded Warrants For Common Stock Issued And Outstanding (Details) - Pre-funded Warrants	6 Months Ended
	Jun. 30, 2020 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Warrants Outstanding	17,610,328
February 8, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issue Date	Feb. 08, 2019
Expiration Date	None
Exercise Price \| $ / shares	$ 0.0001
Number of Warrants Outstanding	4,000,000
April 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issue Date	Apr. 30, 2020
Expiration Date	None
Exercise Price \| $ / shares	$ 0.0001
Number of Warrants Outstanding	13,610,328

License Agreements - Additional Information (Details) - License Agreements $ in Millions	1 Months Ended	6 Months Ended
	Jan. 31, 2017 USD ($) LicenseAgreement	Jun. 30, 2020
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research agreement date		2013-12
Number of license agreements \| LicenseAgreement	2
Maximum future contingent license payment	$ 6.4
Aggregate potential milestone payments for receipt of regulatory approval	5.0
Aggregate potential milestone payments for final regulatory approval of second indication	$ 0.5
Minimum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Rate of revenue share	6.50%
Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Rate of revenue share	25.00%