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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	May 04, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Registrant Name	89bio, Inc.
Entity Central Index Key	0001785173
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		13,793,858
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Title of 12(b) Security	Common stock, par value $0.001 per share
Trading Symbol	ETNB
Security Exchange Name	NASDAQ
Entity File Number	001-39122
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-4946844
Entity Address, Address Line One	142 Sansome Street
Entity Address, Address Line Two	Second Floor
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94104
City Area Code	415
Local Phone Number	500-4614
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 85,532	$ 93,335
Restricted cash	24	25
Prepaid and other current assets	1,857	1,966
Total current assets	87,413	95,326
Property and equipment, net	204	155
Other assets	72	72
Total assets	87,689	95,553
Current liabilities:
Accounts payable	4,055	989
Accrued expenses	3,732	4,620
Total current liabilities	7,787	5,609
Commitments and contingencies (Note 5)
Stockholders’ equity:
Common stock	14	14
Additional paid-in capital	164,028	163,526
Accumulated deficit	(84,140)	(73,596)
Total stockholders’ equity	79,902	89,944
Total liabilities and stockholders’ equity	$ 87,689	$ 95,553

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating expenses:
Research and development	$ 7,778	$ 4,309
General and administrative	2,924	523
Total operating expenses	10,702	4,832
Loss from operations	10,702	4,832
Other income, net	(157)	(416)
Net loss before tax	10,545	4,416
Income tax (benefit) expense	(1)	23
Net loss and comprehensive loss	$ 10,544	$ 4,439
Net loss per share, basic and diluted	$ 0.76	$ 7.26
Weighted-average shares used to compute net loss per share, basic and diluted	13,789,786	611,226

Condensed Consolidated Statements of Convertible Preferred Stock, and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Convertible Preferred Stock
Beginning balance at Dec. 31, 2018	$ (16,057)	$ 1	$ 118	$ (16,176)
Beginning balance, shares at Dec. 31, 2018					24,000,000
Beginning balance at Dec. 31, 2018					$ 23,073
Beginning balance, shares at Dec. 31, 2018		611,226
Share-based compensation	35		35	0
Net loss and comprehensive loss	(4,439)		0	(4,439)
Ending balance at Mar. 31, 2019	(20,461)	$ 1	153	(20,615)
Ending balance, shares at Mar. 31, 2019					24,000,000
Ending balance at Mar. 31, 2019					$ 23,073
Ending balance, shares at Mar. 31, 2019		611,226
Beginning balance at Dec. 31, 2019	$ 89,944	$ 14	163,526	(73,596)
Beginning balance, shares at Dec. 31, 2019	0				0
Beginning balance at Dec. 31, 2019					$ 0
Beginning balance, shares at Dec. 31, 2019		13,788,982
Issuance of common stock upon exercise of stock options	$ 9	$ 0	9	0
Issuance of common stock upon exercise of stock options, shares	4,876	4,876
Share-based compensation	$ 493		493	0
Net loss and comprehensive loss	(10,544)		0	(10,544)
Ending balance at Mar. 31, 2020	$ 79,902	$ 14	$ 164,028	$ (84,140)
Ending balance, shares at Mar. 31, 2020	0				0
Ending balance at Mar. 31, 2020					$ 0
Ending balance, shares at Mar. 31, 2020		13,793,858

- Definition

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

+ References + Details

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (10,544)	$ (4,439)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	12	3
Share-based compensation	493	35
Deferred tax assets		(19)
Revaluation of convertible preferred stock liability		(437)
Changes in operating assets and liabilities:
Prepaids and other current assets	109	(82)
Accounts payable	3,066	(427)
Accrued expenses	(888)	1,199
Net cash used in operating activities	(7,752)	(4,167)
Cash flows from investing activities:
Purchases of property and equipment	(61)	(2)
Net cash used in investing activities	(61)	(2)
Cash flows from financing activities:
Proceeds from issuance of common stock upon exercise of stock options	9
Net cash provided by financing activities	9
Net decrease in cash and cash equivalents, and restricted cash	(7,804)	(4,169)
Cash and cash equivalents, and restricted cash at beginning of period	93,360	11,257
Cash and cash equivalents, and restricted cash at end of period	85,556	7,088
Components of cash and cash equivalents, and restricted cash:
Cash and cash equivalents	85,532	7,064
Restricted cash	24	24
Cash and cash equivalents, and restricted cash at end of period	85,556	$ 7,088
Noncash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued expenses	$ 54

Organization and Basis of Presentation

3 Months Ended

Mar. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Basis of Presentation

1. Organization and Basis of Presentation

Description of Business

89bio, Inc. (“89bio” or the “Company”) is a clinical-stage biopharmaceutical company focused on the development and commercialization of innovative therapies for the treatment of liver and cardio-metabolic diseases. The Company’s lead product candidate, BIO89-100, a specifically engineered glycoPEGylated analog of fibroblast growth factor 21, is currently being developed for the treatment of nonalcoholic steatohepatitis.

89bio, Inc. was formed as a Delaware corporation on June 28, 2019, for the purpose of completing an initial public offering (“IPO”) and related transactions in order to carry on the business of 89Bio Ltd., which was incorporated in Israel in January 2018.

The Company completed an internal reorganization transaction in September 2019, pursuant to which 89Bio Ltd. became a wholly owned subsidiary of 89bio, Inc. (the “Reorganization”). As part of the Reorganization, all of the equity holders of 89Bio Ltd. exchanged 100% of the equity of 89Bio Ltd. for 100% of the equity of 89bio, Inc. The Reorganization was considered a transaction between entities under common control.

Initial Public Offering

On November 13, 2019, 89bio, Inc. completed the IPO, pursuant to which it issued and sold an aggregate of 6,100,390 shares of common stock (inclusive of 795,703 shares pursuant to the underwriters’ option to purchase additional shares) at the IPO price of $16.00 per share, resulting in net proceeds of $87.7 million after deducting underwriting discounts and commissions of $6.8 million and other offering expenses of $3.1 million. Upon the closing of the IPO, the Company’s outstanding convertible preferred stock automatically converted into 7,077,366 shares of common stock of 89bio, Inc. based on a proportional adjustment to the conversion ratio of the convertible preferred stock on a 1-for-6.217 basis.

Liquidity

The accompanying condensed consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and liquidation of liabilities in the normal course of business. To date, the Company has not generated revenues from its activities and has incurred substantial operating losses. Management expects the Company to continue to generate substantial operating losses for the foreseeable future until it completes development of its products and seeks regulatory approvals to market such products. The Company had cash and cash equivalents of $85.5 million as of March 31, 2020. Management expects to continue to fund its operations primarily through utilization of its current financial resources and through additional raises of capital.

The Company intends to raise such capital through the issuance of additional equity financing and/or debt financing. However, if such financing is not available at adequate levels, the Company will need to reevaluate its operating plan and may be required to delay the development of its products. The Company expects that its cash and cash equivalents as of March 31, 2020 will be sufficient to fund operating expenses and capital expenditure requirements for a period of at least one year from the date these unaudited condensed consolidated financial statements are filed with the Securities and Exchange Commission (“SEC”).

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Unaudited Condensed Consolidated Financial Statements

The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“U.S. GAAP”) and applicable rules and regulations of the SEC regarding interim financial reporting.

The accompanying interim condensed consolidated financial statements are unaudited. The interim unaudited condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements as of and for the year ended December 31, 2019 and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s consolidated financial position, results of operations and comprehensive loss, and cash flows. The results of operations for the three months ended March 31, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any other future annual or interim period. The condensed consolidated balance sheet as of December 31, 2019 was derived from the audited financial statements as of that date. These condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements included in the Annual Report on Form 10-K for the year ended December 31, 2019, which was filed with the SEC on March 18, 2020.

Principles of Consolidation

The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include but are not limited to the fair value of stock options, the convertible preferred stock liability and certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates.

Fair Value Measurements

Financial assets and liabilities are recorded at fair value on a recurring basis in the balance sheets. The carrying values of Company’s financial assets and liabilities, including cash and cash equivalents, restricted cash, prepaid and other current assets, accounts payable, and accrued expenses approximate their fair values due to the short-term maturity of these instruments. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. Assets and liabilities recorded at fair value are categorized based upon the level of judgment associated with the inputs used to measure their fair value. Hierarchical levels are directly related to the amount of subjectivity with the inputs to the valuation of these assets or liabilities as follows:

Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date;

Level 2—Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable inputs for similar assets or liabilities. These include quoted prices for identical or similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active;

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Convertible Preferred Stock Liability

The freestanding instruments related to the commitment by the Series A convertible preferred stockholders to purchase and by the Company to sell its Series A convertible preferred stock in subsequent closings, contingent upon the achievement of certain developmental milestones and approval by the board of directors, at a fixed price per stock, were considered a liability (or an asset), measured at fair value as the shares underlying the rights contained liquidation preferences upon certain “deemed liquidation events” that were not solely within the Company’s control and which were considered in-substance contingent redemption features. The instruments were subject to revaluation at each balance sheet date until settlement or extinguishment, with revaluations recognized as either a component of other income, net in the condensed consolidated statements of operations and comprehensive loss, or additional paid-in capital in the condensed consolidated balance sheets. Upon the completion of the Company’s IPO, the remaining shares of convertible preferred stock that were previously issuable under the third closing were no longer issuable. Accordingly, the preferred stock liability was extinguished and because the transaction occurred between related parties, the resulting $25.6 million was accounted for as a capital contribution by the preferred stockholders.

Risk and Uncertainties

In December 2019, a novel strain of coronavirus, SARS-CoV-2, causing a disease referred to as COVID-19, was reported to have surfaced in Wuhan, China. Since then, COVID-19 has spread to other countries, including the United States, and has been declared a pandemic by the World Health Organization.

If COVID-19 continues to spread in the United States and worldwide, the Company may experience disruptions that could negatively impact its ability to recruit and onboard new employees and productivity, disrupt the business and delay preclinical and clinical programs and timelines, the magnitude of which will depend, in part, on the length and severity of restrictions and limitations on the Company’s ability to conduct business in the ordinary course. At this point, the extent to which COVID-19 may impact the Company’s operating results and financial condition is uncertain.

Recently Adopted Accounting Pronouncement

In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, which amends ASC 820, Fair Value Measurement. This ASU modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. The Company adopted this standard effective from January 1, 2020, with the removed and modified disclosures adopted on a retrospective basis and the new disclosures adopted on a prospective basis. The standard did not have a material impact on the Company’s consolidated financial statements and related disclosures.

Recent Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02—Leases (“ASU 2016-02”), requiring the recognition of lease assets and liabilities on the balance sheet. The standard: (a) clarifies the definition of a lease; (b) requires a dual approach to lease classification similar to current lease classifications; and (c) causes lessees to recognize leases on the balance sheet as a lease liability with a corresponding right-of-use asset for leases with a lease-term of more than twelve months. The standard is effective for public entities for fiscal years beginning after December 15, 2018 and for nonpublic entities for fiscal years beginning after December 15, 2020. As an emerging growth company, ASU 2016-02 is effective for the Company for the year ending December 31, 2021 and interim periods within the year ending December 31, 2022. The Company is currently evaluating the impact of this standard on its consolidated financial statements and related disclosures.

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard is effective for public entities for fiscal years beginning after December 15, 2020 and for nonpublic entities for fiscal years beginning after December 15, 2021. As an emerging growth company, ASU 2019-12 is effective for the Company for the year ending December 31, 2022 and interim periods within the year ending December 31, 2023. The Company is currently evaluating the impact of this standard on its consolidated financial statements and related disclosures.

Fair Value Measurements

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The Company’s convertible preferred stock liability represented a Level 3 financial liability measured at fair value on a recurring basis prior to its extinguishment as of December 31, 2019. Accordingly, there was no Level 3 financial liability as of March 31, 2020.

For the three months ended March 31, 2019, changes in the fair value of the Company’s Level 3 financial liability were measured on a recurring basis as follows (in thousands):

	Three Months Ended
	March 31, 2019
Beginning balance	$	1,671
Revaluation of convertible preferred stock liability recorded in other income, net		(437	)
Ending balance	$	1,234

The Company’s convertible preferred stock liability resulted from the initial sale of Series A convertible preferred stock where the investors committed to purchase additional shares of Series A convertible preferred stock in subsequent closings, contingent upon the achievement by the Company of certain development milestones and approval by the board of directors. The investors’ commitment to purchase and the Company’s commitment to sell shares of Series A convertible preferred stock represented a freestanding instrument accounted for at fair value and re-measured at each reporting date. The Company estimated the fair value of this commitment using the Black-Scholes option-pricing model using the following assumptions:

	Three Months Ended
	March 31, 2019
Stock price	$	0.99
Exercise price	$	1.00
Expected term (years)	0.24-2.25
Expected volatility		72.0	%
Risk-free interest rate	2.3-2.4		%

- 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

Consolidated Balance Sheet Components

3 Months Ended

Mar. 31, 2020

Balance Sheet Related Disclosures [Abstract]

Consolidated Balance Sheet Components

4. Consolidated Balance Sheet Components

Accrued Expenses

Accrued expenses consist of the following (in thousands):

	March 31,		December 31,
	2020		2019
Accrued research and development expense	$	2,169	$	2,326
Accrued employee and related expenses		730		1,396
Accrued professional and legal fees		552		573
Accrued other		281		325
Total accrued expenses	$	3,732	$	4,620

Commitments and Contingencies

3 Months Ended

Mar. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

5. Commitments and Contingencies

Leases

Future minimum lease payments under the Company’s non-cancellable operating lease obligations as of March 31, 2020, are as follows (in thousands):


Remainder of 2020	$	161
2021		216
2022		8
Total future minimum annual payments	$	385

Rent expense was $60,000 and $27,000 for the three months ended March 31, 2020 and 2019, respectively.

Asset Transfer and License Agreement with Teva Pharmaceutical Industries Ltd

In April 2018, the Company concurrently entered into two Asset Transfer and License Agreements (the “Teva Agreements”) with Teva Pharmaceutical Industries Ltd (“Teva”) under which it acquired certain patents and intellectual property relating to two programs: (1) Teva’s glycoPEGylated FGF21 program, including the compound TEV-47948 (BIO89-100), a glycoPEGylated long-acting FGF21 and (2) Teva’s development program of small molecule inhibitors of Fatty Acid Synthase. Pursuant to the Teva Agreements, the Company paid Teva an initial nonrefundable upfront payment of $6.0 million and the Company could be obligated to pay Teva up to $67.5 million under each program, for a total of $135.0 million, upon the achievement of certain clinical development and commercial milestones. In addition, the Company is obligated to pay Teva tiered royalties at percentages in the low-to-mid single-digits on worldwide net sales on all products containing the Teva compounds.

The Teva Agreements can be terminated (i) by the Company without cause, after the first anniversary of the effective date, upon 120 days’ written notice to Teva, (ii) by either party, if the other party materially breaches any of its obligations under the Agreements and fails to cure such breach within 60 days after receiving notice thereof, or (iii) by either party, if a bankruptcy petition is filed against the other party and is not dismissed within 60 days. In addition, Teva can also terminate the agreement related to the Company’s glycoPEGylated FGF21 program in the event the Company, or any of its affiliates or sublicensees, challenges any of the Teva patents licensed to the Company, and the challenge is not withdrawn within 30 days of written notice from Teva.

The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the total consideration transferred to Teva as research and development expense in the condensed consolidated statements of operations and comprehensive loss because the acquired technology represented in-process research and development and had no alternative future use. During the three months ended March 31, 2020 and 2019, there were no license payment expenses related to the Teva Agreements.

Convertible Preferred Stock

3 Months Ended

Mar. 31, 2020

Temporary Equity Disclosure [Abstract]

Convertible Preferred Stock

6. Convertible Preferred Stock

In April 2018, the Company entered into the Series A Share Purchase Agreement (the “Series A SPA”), pursuant to which the investors committed to invest an aggregate amount of up to $60.0 million for the issuance of shares of Series A convertible preferred stock at a price of $1.00 per share.

The initial closing occurred on April 16, 2018, and the Company issued 14,900,000 shares of Series A convertible preferred stock at a price per share of $1.00 for net cash proceeds of $14.7 million. In addition, a convertible note in the amount of $100,000 that was outstanding and automatically convertible in the Company’s next equity financing, converted into 100,000 shares of Series A convertible preferred stock upon the initial closing of the Series A financing. The investors also committed to purchase 15,000,000 and 30,000,000 shares of Series A convertible preferred stock at a price of $1.00 per share in second and third closings, respectively, contingent upon the achievement by the Company of certain development milestones and approval by the board of directors.

The investors’ commitment to purchase and the Company’s commitment to sell shares of Series A convertible preferred stock represent a freestanding instrument accounted for at fair value and re-measured at each reporting date. For the three months ended March 31, 2020 and 2019, the Company recorded a gain of $0 and $437,000, respectively, for the revaluation of the convertible preferred stock liability within other income, net in the condensed consolidated statements of operations and comprehensive loss.

In December 2018 and in June 2019, the Company and the Series A convertible preferred stockholders agreed to issue 9,000,000 and 20,000,000 shares of Series A convertible preferred stock at a price of $1.00 per share, respectively, related to the second and third closings. Aggregate net proceeds of $9.0 million were received in December 2018 and $20.0 million were received in June and July 2019.

On October 25, 2019, the Company and the Series A preferred stockholders amended the Series A SPA, and the parties agreed that the Series A SPA would terminate upon consummation of the Company’s IPO.

Upon the completion of the Company’s IPO on November 13, 2019, the remaining 16,000,000 shares of convertible preferred stock that were previously issuable under the third closing were no longer issuable. Accordingly, the preferred stock liability was extinguished and because the transaction occurred between related parties, the resulting $25.6 million was accounted for as a capital contribution by the preferred stockholders.

Additionally, immediately prior to the completion of the Company’s IPO, all outstanding shares of convertible preferred stock automatically converted into 7,077,366 shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. Accordingly, there were no shares of convertible preferred stock outstanding as of March 31, 2020 and December 31, 2019.

Share-Based Compensation

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation

7. Share-Based Compensation

Equity Incentive Plans

In 2018, the Company’s board of directors adopted the 89Bio Ltd. 2018 Equity Incentive Plan (the “2018 Plan”). In connection with the Reorganization, in September 2019, the Company’s board of directors approved the 2019 Equity Incentive Plan (the “2019 Plan”), which became effective on September 17, 2019. From and after the effective date of the 2019 Plan, the Company will no longer be making any future awards under the 2018 Plan.

The Company initially reserved 2,844,193 shares of common stock for issuance under the 2019 Plan. In addition, the number of shares of common stock reserved for issuance under the 2019 Plan will automatically increase on the first day of January for a period of up to ten years, commencing on January 1, 2020, in an amount equal to 4% of the total number of shares of the Company’s capital stock outstanding on the immediately preceding December 31, or a lesser number of shares determined by the Company’s board of directors. As of March 31, 2020, there were 1,676,191 shares of common stock available for issuance as future option grants under the 2019 Plan.

Employee Stock Purchase Plan (ESPP)

In October 2019, the Company adopted the 2019 Employee Stock Purchase Plan (“ESPP”), which became effective following the date of the IPO. The Company initially reserved 225,188 shares of common stock for purchase under the ESPP. The number of shares of common stock reserved for issuance under the ESPP will automatically increase on the first day of January for a period of up to ten years, in an amount equal to 1% of the total number of shares of the Company’s common stock outstanding on the immediately preceding December 31, or a lesser number of shares determined by the Company’s board of directors. Purchases will be accomplished through the participation of discrete offering periods. Each offering will be no more than 27 months long. For each offering period, ESPP participants will purchase shares of common stock at a price per share equal to 85% of the lesser of the fair market value of the Company’s common stock on (1) the first trading day of the applicable offering period or (2) the last trading day of each purchase period the applicable offering period.

The first six month offering period pursuant to the ESPP commenced on January 1, 2020. Total share-based compensation related to the ESPP for the three months ended March 31, 2020 was $13,000. As of March 31, 2020, 363,078 shares of common stock were available for issuance under the ESPP.

The Company recorded share-based compensation for the periods indicated as follows (in thousands):

	Three Months Ended
	March 31,
	2020		2019
Research and development	$	192	$	7
General and administrative		301		28
Total share-based compensation	$	493	$	35

The fair value of option awards granted for the periods indicated was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended
	March 31,
	2020			2019
Stock Options
Expected term (years)	6.00-6.11				6.11
Expected volatility	86.4-87.5		%		61.8	%
Risk-free interest rate	0.5-1.5		%	2.5-2.6		%
Expected dividend		—			—

The following table summarizes stock option activity for the three months ended March 31, 2020:

						Weighted
				Weighted		Average
				Average		Remaining		Aggregate
	Number of			Exercise		Contractual		Intrinsic
	Options			Price		Term		Value
						(In years)		(In thousands)
Balance outstanding as of December 31, 2019		1,320,243		$	3.34		9.23	$	30,353
Granted		439,800			31.66
Exercised		(4,876	)		1.93
Cancelled		(40,482	)		2.87
Balance outstanding as of March 31, 2020		1,714,685			10.62		9.21	$	28,115
Exercisable as of March 31, 2020		299,571		$	2.00		8.69	$	6,850

Net Loss Per Share

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Net Loss Per Share

8. Net Loss Per Share

Basic net loss per share is computed by dividing net loss by the weighted-average number of common shares outstanding for the period. Since the Company was in a loss position for all periods presented, diluted net loss per share is the same as basic net loss per share for all periods as the inclusion of all potential shares of common stock outstanding would have been anti-dilutive.

The following outstanding potentially dilutive common stock equivalents have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect:

	Three Months Ended
	March 31,
	2020		2019
Stock options to purchase common stock		1,714,685		734,569
Employee stock purchase plan		1,735		—
Convertible preferred stock, as converted		—		3,860,383
Total		1,716,420		4,594,952

Related Party Transactions

3 Months Ended

Mar. 31, 2020

Related Party Transactions

9. Related Party Transactions

The Company incurred $4,000 and $33,000 in professional consulting services expense related to certain members of the board of directors for the three months ended March 31, 2020 and 2019, respectively, which is recorded within research and development expenses in the Company’s condensed consolidated statements of operations and comprehensive loss. The related party liability balance was $0 as of March 31, 2020 and $11,000 as of December 31, 2019, respectively, which is recorded within accounts payable and accrued expenses in the Company’s condensed consolidated balance sheets.

The Company and the Series A preferred stockholders amended the Series A SPA on October 25, 2019, and the parties agreed that the Series A SPA would terminate upon consummation of the Company’s IPO. Upon the completion of the Company’s IPO on November 13, 2019, the remaining 16,000,000 shares of convertible preferred stock that were issuable were no longer issuable. Accordingly, the preferred stock liability was extinguished and because the transaction occurred between related parties, the resulting $25.6 million was accounted for as a capital contribution by the preferred stockholders and recorded as part of additional paid-in capital in the condensed consolidated balance sheets (see Note 6).

Subsequent Event

3 Months Ended

Mar. 31, 2020

Subsequent Events [Abstract]

Subsequent Event

10. Subsequent Event

On April 7, 2020, the Company and certain of its subsidiaries entered into a Loan and Security Agreement (the “Loan Agreement”) with the lenders referred to therein (the “Lenders”), and Silicon Valley Bank, as collateral agent. The Loan Agreement provides for (i) a secured term A loan facility (the “Term A Loan Facility”) of up to $10.0 million and (ii) a secured term B loan facility (the “Term B Loan Facility”) of up to $5.0 million that is available upon the Company satisfying certain milestones. The Term A Loan Facility matures on November 1, 2022; provided, that if the Term B Loan Facility is funded, the facilities instead mature on September 1, 2023. The loan will bear interest at the greater of (i) 4.50% and (ii) the sum of (a) the Prime Rate as reported in The Wall Street Journal plus (b) 1.25%.

In addition, under the Loan Agreement, the Company agreed to issue the Lenders warrants to purchase shares of the Company’s common stock. On April 7, 2020, warrants to purchase 25,000 shares of the Company’s common stock were issued with a warrant exercise price of $22.06 per share. Additional warrants exercisable for 8,333 shares of common stock will be issued in connection with the Term B Loan Facility, if funded.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2020
Accounting Policies [Abstract]
Unaudited Condensed Consolidated Financial Statements	Unaudited Condensed Consolidated Financial Statements The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“U.S. GAAP”) and applicable rules and regulations of the SEC regarding interim financial reporting. The accompanying interim condensed consolidated financial statements are unaudited. The interim unaudited condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements as of and for the year ended December 31, 2019 and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s consolidated financial position, results of operations and comprehensive loss, and cash flows. The results of operations for the three months ended March 31, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any other future annual or interim period. The condensed consolidated balance sheet as of December 31, 2019 was derived from the audited financial statements as of that date. These condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements included in the Annual Report on Form 10-K for the year ended December 31, 2019, which was filed with the SEC on March 18, 2020.
Principles of Consolidation	Principles of Consolidation The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include but are not limited to the fair value of stock options, the convertible preferred stock liability and certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates.
Fair Value Measurements	Fair Value Measurements Financial assets and liabilities are recorded at fair value on a recurring basis in the balance sheets. The carrying values of Company’s financial assets and liabilities, including cash and cash equivalents, restricted cash, prepaid and other current assets, accounts payable, and accrued expenses approximate their fair values due to the short-term maturity of these instruments. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. Assets and liabilities recorded at fair value are categorized based upon the level of judgment associated with the inputs used to measure their fair value. Hierarchical levels are directly related to the amount of subjectivity with the inputs to the valuation of these assets or liabilities as follows: Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2—Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable inputs for similar assets or liabilities. These include quoted prices for identical or similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active; Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
Convertible Preferred Stock Liability	Convertible Preferred Stock Liability The freestanding instruments related to the commitment by the Series A convertible preferred stockholders to purchase and by the Company to sell its Series A convertible preferred stock in subsequent closings, contingent upon the achievement of certain developmental milestones and approval by the board of directors, at a fixed price per stock, were considered a liability (or an asset), measured at fair value as the shares underlying the rights contained liquidation preferences upon certain “deemed liquidation events” that were not solely within the Company’s control and which were considered in-substance contingent redemption features. The instruments were subject to revaluation at each balance sheet date until settlement or extinguishment, with revaluations recognized as either a component of other income, net in the condensed consolidated statements of operations and comprehensive loss, or additional paid-in capital in the condensed consolidated balance sheets. Upon the completion of the Company’s IPO, the remaining shares of convertible preferred stock that were previously issuable under the third closing were no longer issuable. Accordingly, the preferred stock liability was extinguished and because the transaction occurred between related parties, the resulting $25.6 million was accounted for as a capital contribution by the preferred stockholders.
Risk and Uncertainties	Risk and Uncertainties In December 2019, a novel strain of coronavirus, SARS-CoV-2, causing a disease referred to as COVID-19, was reported to have surfaced in Wuhan, China. Since then, COVID-19 has spread to other countries, including the United States, and has been declared a pandemic by the World Health Organization. If COVID-19 continues to spread in the United States and worldwide, the Company may experience disruptions that could negatively impact its ability to recruit and onboard new employees and productivity, disrupt the business and delay preclinical and clinical programs and timelines, the magnitude of which will depend, in part, on the length and severity of restrictions and limitations on the Company’s ability to conduct business in the ordinary course. At this point, the extent to which COVID-19 may impact the Company’s operating results and financial condition is uncertain.
Recently Adopted Accounting Pronouncement	Recently Adopted Accounting Pronouncement In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, which amends ASC 820, Fair Value Measurement. This ASU modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. The Company adopted this standard effective from January 1, 2020, with the removed and modified disclosures adopted on a retrospective basis and the new disclosures adopted on a prospective basis. The standard did not have a material impact on the Company’s consolidated financial statements and related disclosures.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02—Leases (“ASU 2016-02”), requiring the recognition of lease assets and liabilities on the balance sheet. The standard: (a) clarifies the definition of a lease; (b) requires a dual approach to lease classification similar to current lease classifications; and (c) causes lessees to recognize leases on the balance sheet as a lease liability with a corresponding right-of-use asset for leases with a lease-term of more than twelve months. The standard is effective for public entities for fiscal years beginning after December 15, 2018 and for nonpublic entities for fiscal years beginning after December 15, 2020. As an emerging growth company, ASU 2016-02 is effective for the Company for the year ending December 31, 2021 and interim periods within the year ending December 31, 2022. The Company is currently evaluating the impact of this standard on its consolidated financial statements and related disclosures. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard is effective for public entities for fiscal years beginning after December 15, 2020 and for nonpublic entities for fiscal years beginning after December 15, 2021. As an emerging growth company, ASU 2019-12 is effective for the Company for the year ending December 31, 2022 and interim periods within the year ending December 31, 2023. The Company is currently evaluating the impact of this standard on its consolidated financial statements and related disclosures.

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Summary of Changes in Fair Value of Level 3 Liability

For the three months ended March 31, 2019, changes in the fair value of the Company’s Level 3 financial liability were measured on a recurring basis as follows (in thousands):

	Three Months Ended
	March 31, 2019
Beginning balance	$	1,671
Revaluation of convertible preferred stock liability recorded in other income, net		(437	)
Ending balance	$	1,234

Summary of Fair Value Assumptions

The Company estimated the fair value of this commitment using the Black-Scholes option-pricing model using the following assumptions:

	Three Months Ended
	March 31, 2019
Stock price	$	0.99
Exercise price	$	1.00
Expected term (years)	0.24-2.25
Expected volatility		72.0	%
Risk-free interest rate	2.3-2.4		%

Consolidated Balance Sheet Components (Tables)

3 Months Ended

Mar. 31, 2020

Balance Sheet Related Disclosures [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following (in thousands):

	March 31,		December 31,
	2020		2019
Accrued research and development expense	$	2,169	$	2,326
Accrued employee and related expenses		730		1,396
Accrued professional and legal fees		552		573
Accrued other		281		325
Total accrued expenses	$	3,732	$	4,620

Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Obligations

Future minimum lease payments under the Company’s non-cancellable operating lease obligations as of March 31, 2020, are as follows (in thousands):


Remainder of 2020	$	161
2021		216
2022		8
Total future minimum annual payments	$	385

Share-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Share-Based Compensation

The Company recorded share-based compensation for the periods indicated as follows (in thousands):

	Three Months Ended
	March 31,
	2020		2019
Research and development	$	192	$	7
General and administrative		301		28
Total share-based compensation	$	493	$	35

Summary of Estimated Fair Value of Option Awards Granted Using Black-Scholes Option-Pricing Model

The fair value of option awards granted for the periods indicated was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended
	March 31,
	2020			2019
Stock Options
Expected term (years)	6.00-6.11				6.11
Expected volatility	86.4-87.5		%		61.8	%
Risk-free interest rate	0.5-1.5		%	2.5-2.6		%
Expected dividend		—			—

Summary of Stock Option Activity

The following table summarizes stock option activity for the three months ended March 31, 2020:

						Weighted
				Weighted		Average
				Average		Remaining		Aggregate
	Number of			Exercise		Contractual		Intrinsic
	Options			Price		Term		Value
						(In years)		(In thousands)
Balance outstanding as of December 31, 2019		1,320,243		$	3.34		9.23	$	30,353
Granted		439,800			31.66
Exercised		(4,876	)		1.93
Cancelled		(40,482	)		2.87
Balance outstanding as of March 31, 2020		1,714,685			10.62		9.21	$	28,115
Exercisable as of March 31, 2020		299,571		$	2.00		8.69	$	6,850

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Schedule of Outstanding Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss

	Three Months Ended
	March 31,
	2020		2019
Stock options to purchase common stock		1,714,685		734,569
Employee stock purchase plan		1,735		—
Convertible preferred stock, as converted		—		3,860,383
Total		1,716,420		4,594,952

Organization and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands		3 Months Ended
	Nov. 13, 2019 USD ($) $ / shares shares	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)
Subsidiary Sale Of Stock [Line Items]
Date of incorporation		Jun. 28, 2019
Reorganization exchange of equity percentage of ordinary shares exchanged		100.00%
Reorganization exchange of equity percentage of common stock issued upon exchange		100.00%
Reverse stock split conversion ratio	0.160849
Cash and cash equivalents		$ 85,532	$ 93,335	$ 7,064
Common Stock
Subsidiary Sale Of Stock [Line Items]
Convertible preferred stock automatically converted into common stock \| shares	7,077,366
IPO \| Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold \| shares	6,100,390
IPO price per share \| $ / shares	$ 16.00
Proceeds from issuance of common stock, net of underwriters discount and commissions	$ 87,700
Payment of underwriting discounts, commissions	6,800
Other offering expenses	$ 3,100
Underwriters option \| Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold \| shares	795,703

Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions	Nov. 13, 2019 USD ($)
Accounting Policies [Abstract]
Capital contribution related to extinguishment of preferred stock liability	$ 25.6

Fair Value Measurements - Additional Information (Details)	Mar. 31, 2020 USD ($)
Level 3
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, financial liability	$ 0

Fair Value Measurements - Summary of Changes in Fair Value of Level 3 Liability (Details) - Recurring - Level 3 $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 1,671
Revaluation of convertible preferred stock liability recorded in other income, net	(437)
Ending balance	$ 1,234

Fair Value Measurements - Summary of Fair Value Assumptions (Details) - Convertible Preferred Stock Liability - Black Scholes Option Pricing Model	3 Months Ended
	Mar. 31, 2019 $ / shares
Stock Price
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	0.99
Exercise Price
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	1.00
Expected Term (Years) \| Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	2 months 26 days
Expected Term (Years) \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	2 years 3 months
Expected Volatility
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	72.0
Risk-free Interest Rate \| Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	2.3
Risk-free Interest Rate \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	2.4

Consolidated Balance Sheet Components - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued research and development expense	$ 2,169	$ 2,326
Accrued employee and related expenses	730	1,396
Accrued professional and legal fees	552	573
Accrued other	281	325
Total accrued expenses	$ 3,732	$ 4,620

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Obligations (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Remainder of 2020	$ 161
2021	216
2022	8
Total future minimum annual payments	$ 385

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended
	Apr. 30, 2018	Mar. 31, 2020	Mar. 31, 2019
Loss Contingencies [Line Items]
Operating leases, rent expense		$ 60,000	$ 27,000
Teva Agreements
Loss Contingencies [Line Items]
Nonrefundable upfront payment	$ 6,000,000
Payment upon achievement of certain clinical and commercial milestones	135,000,000
Asset transfer and license agreement, termination period after written notice			120 days
Asset transfer and license agreement, termination period notice of breach			60 days
Asset transfer and license agreement termination notice period if bankruptcy petition filed			60 days
Teva Agreements \| Research and Development Expenses
Loss Contingencies [Line Items]
Up-front license payment		$ 0	$ 0
Teva Agreements \| Teva’s GlycoPEGylated FGF21 Program
Loss Contingencies [Line Items]
Payment upon achievement of certain clinical and commercial milestones	67,500,000
Teva Agreements \| Teva’s Development Program
Loss Contingencies [Line Items]
Payment upon achievement of certain clinical and commercial milestones	$ 67,500,000

Convertible Preferred Stock - Additional Information (Details) - USD ($)			1 Months Ended	2 Months Ended	3 Months Ended
	Nov. 13, 2019	Apr. 16, 2018	Dec. 31, 2018	Jul. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Jun. 30, 2019	Apr. 30, 2018
Temporary Equity [Line Items]
Capital contribution related to extinguishment of preferred stock liability	$ 25,600,000
Convertible preferred stock outstanding					0		0
Common Stock
Temporary Equity [Line Items]
Convertible preferred stock automatically converted into common stock	7,077,366
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Number of shares committed to purchase, no longer issuable	16,000,000
Series A Share Purchase Agreement
Temporary Equity [Line Items]
Convertible note outstanding amount converted into shares		100,000
Series A Share Purchase Agreement \| Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Per share price of issuance of shares									$ 1.00
Convertible note outstanding amount converted into shares		100,000
Series A Share Purchase Agreement \| Series A Convertible Preferred Stock \| Other Income, Net
Temporary Equity [Line Items]
Gain recorded for revaluation of convertible preferred stock liability					$ 0	$ 437,000
Series A Share Purchase Agreement \| Series A Convertible Preferred Stock \| Initial Closing
Temporary Equity [Line Items]
Per share price of issuance of shares		$ 1.00
Shares issued		14,900,000
Net cash proceeds		$ 14,700,000
Series A Share Purchase Agreement \| Series A Convertible Preferred Stock \| Second Closing
Temporary Equity [Line Items]
Per share price of issuance of shares		$ 1.00	$ 1.00
Shares issued			9,000,000
Net cash proceeds			$ 9,000,000
Number of shares committed to purchase		15,000,000
Series A Share Purchase Agreement \| Series A Convertible Preferred Stock \| Third Closing
Temporary Equity [Line Items]
Per share price of issuance of shares		$ 1.00						$ 1.00
Shares issued								20,000,000
Net cash proceeds				$ 20,000,000
Number of shares committed to purchase		30,000,000
Series A Share Purchase Agreement \| Series A Convertible Preferred Stock \| Maximum
Temporary Equity [Line Items]
Total amount of preferred shares issuable by the entity									$ 60,000,000

Share-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended
	Oct. 31, 2019	Sep. 30, 2019	Mar. 31, 2020	Mar. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based compensation			$ 493,000	$ 35,000
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares issuable under the plan (in shares)	225,188
Percentage of increase in number of shares of capital stock issued and outstanding	1.00%
Percent of purchase shares of common stock	85.00%
First offering period	6 months
Commencement date of first six month offering period	Jan. 01, 2020
Total share-based compensation			$ 13,000
Number of shares of common stock available for issuance under ESPP			363,078
2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares issuable under the plan (in shares)		2,844,193
Percentage of increase in number of shares of capital stock issued and outstanding			4.00%
Common stock reserved and available for issuance as future option grants			1,676,191
Maximum \| Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period for increase in number of shares of common stock reserved for issuance	10 years
Maximum \| 2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period for increase in number of shares of common stock reserved for issuance			10 years

Share-Based Compensation - Summary of Share-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	$ 493	$ 35
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	192	7
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	$ 301	$ 28

Share-Based Compensation - Summary of Estimated Fair Value of Option Awards Granted Using Black-Scholes Option-Pricing Model (Details) - Stock Options	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		6 years 1 month 9 days
Expected volatility, minimum	86.40%
Expected volatility, maximum	87.50%
Risk-free interest rate, minimum	0.50%	2.50%
Risk-free interest rate, maximum	1.50%	2.60%
Expected volatility		61.80%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 1 month 9 days

Share-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Number of Options
Outstanding, Beginning Balance	1,320,243
Granted	439,800
Exercised	(4,876)
Cancelled	(40,482)
Outstanding, Ending Balance	1,714,685	1,320,243
Exercisable as of March 31, 2020	299,571
Weighted Average Exercise Price
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 3.34
Weighted Average Exercise Price, Granted	31.66
Weighted Average Exercise Price, Exercised	1.93
Weighted Average Exercise Price, Cancelled	2.87
Weighted Average Exercise Price Outstanding, Ending Balance	10.62	$ 3.34
Weighted Average Exercise Price, Exercisable as of March 31, 2020	$ 2.00
Weighted Average Remaining Contractual Term (In years)
Weighted Average Remaining Contractual Term (In years), Outstanding	9 years 2 months 15 days	9 years 2 months 23 days
Weighted Average Remaining Contractual Term (In years), Exercisable as of March 31, 2020	8 years 8 months 8 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value Outstanding	$ 28,115	$ 30,353
Aggregate Intrinsic Value, Exercisable as of March 31, 2020	$ 6,850

Net Loss Per Share - Schedule of Outstanding Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	1,716,420	4,594,952
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	1,714,685	734,569
Convertible Preferred Stock, as Converted
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share		3,860,383
Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	1,735

Related Party Transactions - Additional Information (Details) - USD ($)		3 Months Ended
	Nov. 13, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Outstanding liability to related party		$ 0		$ 11,000
Capital contribution	$ 25,600,000
Series A Convertible Preferred Stock
Related Party Transaction [Line Items]
Number of shares committed to purchase, no longer issuable	16,000,000
Additional Paid-in Capital
Related Party Transaction [Line Items]
Capital contribution	$ 25,600,000
Board of Directors
Related Party Transaction [Line Items]
Professional services expense		$ 4,000	$ 33,000

Subsequent Event - Additional Information (Details) - Loan Agreement - Subsequent Event	Apr. 07, 2020 USD ($) $ / shares shares
Subsequent Event [Line Items]
Credit facility maturity date	Sep. 01, 2023
Line of credit facility, description	On April 7, 2020, the Company and certain of its subsidiaries entered into a Loan and Security Agreement (the “Loan Agreement”) with the lenders referred to therein (the “Lenders”), and Silicon Valley Bank, as collateral agent. The Loan Agreement provides for (i) a secured term A loan facility (the “Term A Loan Facility”) of up to $10.0 million and (ii) a secured term B loan facility (the “Term B Loan Facility”) of up to $5.0 million that is available upon the Company satisfying certain milestones. The Term A Loan Facility matures on November 1, 2022; provided, that if the Term B Loan Facility is funded, the facilities instead mature on September 1, 2023. The loan will bear interest at the greater of (i) 4.50% and (ii) the sum of (a) the Prime Rate as reported in The Wall Street Journal plus (b) 1.25%.
Prime Rate
Subsequent Event [Line Items]
Debt instrument, basis spread on variable rate	1.25%
Minimum
Subsequent Event [Line Items]
Debt instrument, interest rate	4.50%
Term A Loan Facility
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity \| $	$ 10,000,000
Credit facility maturity date	Nov. 01, 2022
Warrants to purchase common stock \| shares	25,000
Warrant exercise price \| $ / shares	$ 22.06
Term B Loan Facility
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity \| $	$ 5,000,000
Warrants to purchase common stock \| shares	8,333