89bio (ETNB) 10-Q 13 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Nov. 06, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
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		19,878,852
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

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 141,551	$ 93,335
Restricted cash	25	25
Short-term investments	77,602
Prepaid and other current assets	3,360	1,966
Total current assets	222,538	95,326
Property and equipment, net	177	155
Other assets	713	72
Total assets	223,428	95,553
Current liabilities:
Accounts payable	4,086	989
Accrued expenses	5,338	4,620
Total current liabilities	9,424	5,609
Commitments and contingencies (Note 5)
Stockholders’ equity:
Common stock	20	14
Additional paid-in capital	324,501	163,526
Accumulated other comprehensive loss	(3)
Accumulated deficit	(110,514)	(73,596)
Total stockholders’ equity	214,004	89,944
Total liabilities and stockholders’ equity	$ 223,428	$ 95,553

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating expenses:
Research and development	$ 11,208	$ 6,680	$ 27,429	$ 14,154
General and administrative	3,225	1,518	9,379	2,875
Total operating expenses	14,433	8,198	36,808	17,029
Loss from operations	14,433	8,198	36,808	17,029
Other expenses, net	146	10,470	87	21,022
Net loss before tax	14,579	18,668	36,895	38,051
Income tax expense	24	57	23	86
Net loss	14,603	18,725	36,918	38,137
Other comprehensive (income) loss:
Unrealized gain on available-for-sale securities	(7)		(7)
Foreign currency translation adjustments	10		10
Total other comprehensive loss	3		3
Comprehensive loss	$ 14,606	$ 18,725	$ 36,921	$ 38,137
Net loss per share, basic and diluted	$ (0.86)	$ (30.63)	$ (2.49)	$ (62.39)
Weighted-average shares used to compute net loss per share, basic and diluted	16,884,244	611,226	14,809,131	611,226

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity Deficit (Unaudited) - USD ($) $ in Thousands	Total	Public Offerings	Common Stock	Common StockPublic Offerings	Additional Paid-in Capital	Additional Paid-in CapitalPublic Offerings	Accumulated Other Comprehensive Loss	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
Net loss	(4,439)							(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, 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
Net loss	(38,137)
Ending balance at Sep. 30, 2019	(53,971)		$ 1		341			(54,313)
Ending balance, shares at Sep. 30, 2019									44,000,000
Ending balance at Sep. 30, 2019									$ 49,746
Ending balance, shares at Sep. 30, 2019			611,226
Beginning balance at Mar. 31, 2019	(20,461)		$ 1		153			(20,615)
Beginning balance, shares at Mar. 31, 2019									24,000,000
Beginning balance at Mar. 31, 2019									$ 23,073
Beginning balance, shares at Mar. 31, 2019			611,226
Issuance of convertible preferred stock, net of issuance costs									$ 25,095
Issuance of convertible preferred stock, net of issuance costs, shares									18,826,389
Share-based compensation	76				76
Net loss	(14,973)							(14,973)
Ending balance at Jun. 30, 2019	(35,358)		$ 1		229			(35,588)
Ending balance, shares at Jun. 30, 2019									42,826,389
Ending balance at Jun. 30, 2019									$ 48,168
Ending balance, shares at Jun. 30, 2019			611,226
Issuance of convertible preferred stock, net of issuance costs									$ 1,578
Issuance of convertible preferred stock, net of issuance costs, shares									1,173,611
Share-based compensation	112				112
Net loss	(18,725)							(18,725)
Ending balance at Sep. 30, 2019	(53,971)		$ 1		341			(54,313)
Ending balance, shares at Sep. 30, 2019									44,000,000
Ending balance at Sep. 30, 2019									$ 49,746
Ending balance, shares at Sep. 30, 2019			611,226
Beginning balance at Dec. 31, 2019	89,944		$ 14		163,526			(73,596)
Beginning balance, shares at Dec. 31, 2019			13,788,982
Issuance of common stock upon exercise of stock options	9				9
Issuance of common stock upon exercise of stock options, shares			4,876
Share-based compensation	493				493
Net loss	(10,544)							(10,544)
Ending balance at Mar. 31, 2020	79,902		$ 14		164,028			(84,140)
Ending balance, shares at Mar. 31, 2020			13,793,858
Beginning balance at Dec. 31, 2019	$ 89,944		$ 14		163,526			(73,596)
Beginning balance, shares at Dec. 31, 2019			13,788,982
Issuance of common stock upon exercise of stock options, shares	13,403
Issuance of common stock warrant in connection with term loan facility	$ 634
Net loss	(36,918)
Other comprehensive loss	(3)
Ending balance at Sep. 30, 2020	214,004		$ 20		324,501		$ (3)	(110,514)
Ending balance, shares at Sep. 30, 2020			19,878,852
Beginning balance at Mar. 31, 2020	79,902		$ 14		164,028			(84,140)
Beginning balance, shares at Mar. 31, 2020			13,793,858
Issuance of common stock upon exercise of stock options	21				21
Issuance of common stock upon exercise of stock options, shares			6,919
Issuance of common stock upon ESPP purchase	75				75
Issuance of common stock upon ESPP purchase, shares			4,427
Issuance of common stock warrant in connection with term loan facility	634				634
Share-based compensation	910				910
Net loss	(11,771)							(11,771)
Ending balance at Jun. 30, 2020	69,771		$ 14		165,668			(95,911)
Ending balance, shares at Jun. 30, 2020			13,805,204
Issuance of common stock		$ 157,680		$ 6		$ 157,674
Issuance of common stock, shares				6,072,040
Issuance of common stock upon exercise of stock options	5				5
Issuance of common stock upon exercise of stock options, shares			1,608
Share-based compensation	1,154				1,154
Net loss	(14,603)							(14,603)
Other comprehensive loss	(3)						(3)
Ending balance at Sep. 30, 2020	$ 214,004		$ 20		$ 324,501		$ (3)	$ (110,514)
Ending balance, shares at Sep. 30, 2020			19,878,852

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity Deficit (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2019
Stock issuance costs	$ 1,208
Convertible Preferred Stock
Temporary equity, issuance costs		$ 0	$ 0
Temporary equity, partial settlement of convertible preferred stock liability		$ 404	$ 6,269

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited)	9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)
Cash flows from operating activities:
Net loss	$ (36,918,000)	$ (38,137,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	47,000	12,000
Share-based compensation	2,557,000	223,000
Deferred tax assets		(69,000)
Revaluation of convertible preferred stock liability		21,018,000
Amortization of premium on available-for-sale securities	85,000
Amortization of debt issuance costs	154,000
Changes in operating assets and liabilities:
Prepaid and other current assets	(1,404,000)	(314,000)
Accounts payable	2,804,000	1,610,000
Accrued expenses	459,000	1,329,000
Net cash used in operating activities	(32,216,000)	(14,328,000)
Cash flows from investing activities:
Purchases of available-for-sale securities	(78,705,000)
Proceeds from maturities of available-for-sale securities	1,025,000
Purchases of property and equipment	(124,000)	(28,000)
Net cash used in investing activities	(77,804,000)	(28,000)
Cash flows from financing activities:
Proceeds from issuance of common stock upon public offering, net of issuance costs	158,287,000
Proceeds from issuance of convertible preferred stock and convertible preferred stock liability, net of issuance cost		20,000,000
Proceeds from issuance of common stock upon stock option exercises	35,000
Proceeds from issuance of common stock		11,000
Payment of debt issuance costs	(161,000)
Payment of deferred offering costs		(686,000)
Net cash provided by financing activities	158,236,000	19,325,000
Net increase in cash and cash equivalents, and restricted cash	48,216,000	4,969,000
Cash and cash equivalents, and restricted cash at beginning of period	93,360,000	11,257,000
Cash and cash equivalents, and restricted cash at end of period	141,576,000	16,226,000
Components of cash and cash equivalents, and restricted cash:
Cash and cash equivalents	141,551,000	16,188,000
Restricted cash	25,000	38,000
Cash and cash equivalents, and restricted cash at end of period	141,576,000	16,226,000
Supplemental cash flow disclosures:
Issuance of common stock warrant in connection with term loan facility	634,000
Deferred offering costs included in accounts payable and accrued expenses	607,000	$ 942,000
Cash paid for taxes	135,000
ESPP Purchase
Cash flows from financing activities:
Proceeds from issuance of common stock	$ 75,000

Organization and Basis of Prese

Organization and Basis of Presentation	9 Months Ended
	Sep. 30, 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 and for the treatment of severe hypertriglyceridemia. 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 its 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, cash equivalents and short-term investments of $219.2 million as of September 30, 2020. In July 2020, the Company completed an underwritten public offering of 3,047,040 shares of its common stock, including 397,440 shares sold pursuant to the underwriters’ exercise of their option to purchase additional shares, at the public offering price of $27.50. The Company raised a total of $83.8 million in gross proceeds from the offering, or approximately $78.2 million in net proceeds after deducting underwriting discounts and commissions of $5.0 million and offering costs of approximately $0.6 million. In September 2020, the Company completed an underwritten public offering of 3,025,000 shares of its common stock, at a public offering price of $28.00 per share. The Company raised a total of $84.7 million in gross proceeds from the offering, or approximately $79.5 million in net proceeds after deducting underwriting discounts and commissions of $4.6 million and offering costs of approximately $0.6 million. The Company expects that its cash, cash equivalents and short-term investments as of September 30, 2020, together with proceeds available from the Company’s term loan (see Note 6), 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 Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 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. Investments 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. Generally, investments with original maturities beyond three months at the date of purchase are classified as short-term because it is management’s intent to use the investments to fund current operations or to make them available for current operations. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. The Company periodically evaluates whether declines in fair values of its available-for-sale securities below their book value are other-than-temporary. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the available-for-sale security until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale securities before recovery of its amortized cost basis. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in other expenses, net. The cost of investments sold is based on the specific-identification method. There were no realized gains or losses on investments for the periods presented. Interest on available-for-sale securities is included in other expenses, net and was not material for all periods presented. Fair Value Measurements Financial assets and liabilities are recorded at fair value on a recurring basis in the balance sheets. The carrying values of the 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. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market funds and commercial paper that are stated at fair value. 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 expenses, 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 a subsequent 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 Due to the ongoing COVID-19 pandemic, the Company may experience disruptions that could negatively impact the Company’s growth, employee productivity and its ability to recruit and onboard new employees. The pandemic has disrupted and may continue to disrupt the Company’s business and delay its preclinical and clinical programs and timelines. The extent to which the COVID-19 pandemic may impact the Company’s future operating results and financial condition is uncertain. Comprehensive Loss The Company’s comprehensive loss is comprised of changes in unrealized gains (losses) on available-for-sale securities and foreign currency transaction adjustments. 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 Recent Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02— Leases In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The following table presents the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy as of September 30, 2020 (in thousands): September 30, 2020 Valuation Amortized Unrealized Unrealized Hierarchy Cost Gains Losses Fair Value Money market funds Level 1 $ 32,445 $ — $ — $ 32,445 Commercial paper Level 2 45,034 1 (1 ) 45,034 Agency bonds Level 2 28,751 12 (3 ) 28,760 U.S. government bonds Level 2 7,135 1 — 7,136 Corporate debt securities Level 2 5,822 — (3 ) 5,819 U.S. treasury bills Level 2 2,150 — — 2,150 Agency discount securities Level 2 460 — — 460 Municipal bonds Level 2 177 — — 177 Total cash equivalents and available-for-sale securities $ 121,974 $ 14 $ (7 ) $ 121,981 Classified as: Cash equivalents $ 44,379 Short-term investments 77,602 Total cash equivalents and available-for-sale securities $ 121,981 The following table summarizes the Company’s available-for-sale securities by contractual maturity as of September 30, 2020 (in thousands): September 30, 2020 Within one year $ 103,643 After one year through two years 18,338 Total cash equivalents and available-for-sale securities $ 121,981 The Company did not hold any financial assets as of December 31, 2019. 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 in the fourth quarter of 2019. Accordingly, there was no Level 3 financial liability outstanding during the nine months ended and as of September 30, 2020. For the nine months ended September 30, 2019, changes in the fair value of the Company’s Level 3 financial liability were measured on a recurring basis as follows (in thousands): Nine Months Ended September 30, 2019 Beginning balance $ 1,671 Revaluation of convertible preferred stock liability recorded in other expenses, net 21,018 Partial settlement of convertible preferred stock liability in subsequent closings (6,673 ) Ending balance $ 16,016 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 revalued at each reporting date. The Company estimated the fair value of this commitment using the Black-Scholes option-pricing model using the following assumptions: Nine Months Ended September 30, 2019 Stock price $ 0.99 - 1.97 Exercise price $ 1.00 Expected term (years) 0.00 - 2.25 Expected volatility 72.0 % Risk-free interest rate 0.0 - 2.4 %

Consolidated Balance Sheet Comp

Consolidated Balance Sheet Components	9 Months Ended
	Sep. 30, 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): September 30, December 31, 2020 2019 Accrued research and development expense $ 2,602 $ 2,326 Accrued employee and related expenses 1,679 1,396 Accrued professional and legal fees 769 573 Accrued other 288 325 Total accrued expenses $ 5,338 $ 4,620

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	5. Commitments and Contingencies Leases Future minimum September 30, 2020 Remainder of 2020 $ 64 2021 232 2022 8 Total future minimum annual payments $ 304 Rent expense was $61,000 and $48,000 for the three months ended September 30, 2020 and 2019, respectively. Rent expense was $208,000 and $108,000 for the nine months ended September 30, 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. During the three and nine months ended September 30, 2020 and 2019, there were no license payment expenses related to the Teva Agreements.

Term Loan

Term Loan	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Term Loan	6. Term Loan Loan and Security Agreement 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 loans 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%. As of September 30, 2020, the Company had not drawn any amount under the Loan Agreement. In connection with the execution of the Loan Agreement, the Company agreed to issue the Lenders warrants to purchase shares of the Company’s common stock. On April 7, 2020, the Company issued Silicon Valley Bank a warrant to purchase 25,000 shares of the Company’s common stock with a warrant exercise price of $22.06 per share that is immediately exercisable. The initial expiration date of April 7, 2030 was changed to June 30, 2025 in connection with the July 2020 offering. The Company determined the fair value of the warrant at the issuance date by using the Black-Scholes option-pricing model with the following assumptions: risk-free interest rate of 0.75%, no dividends, expected volatility of 92.30% and expected term of 10.0 years. Upon issuance, the fair value allocated to the warrant of $0.6 million was recorded as a debt issuance cost and classified within other assets and met the requirements for equity classification within additional paid-in capital on the consolidated condensed balance sheets. An additional warrant to purchase 8,333 shares of the Company’s common stock will be issued in connection with the Term B Loan Facility, if funded, with the exercise price determined on the Company’s stock price at the time of issuance. Additionally, the Company incurred $0.2 million in closing costs that were recorded as debt issuance costs and classified within other assets on the consolidated condensed balance sheets. The deferred assets related to the debt issuance cost and warrant are recognized as interest expense over the duration of the Loan Agreement and are recorded within other expenses, net on the condensed consolidated statements of operations and comprehensive loss. As of September 30, 2020, the remaining unamortized debt issuance costs classified within other assets on the consolidated condensed balance sheet is $0.6 million.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Stockholders' Equity	7. Stockholders’ Equity 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 September 30, 2020, there were 1,506,991 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 and each offering is expected to be 6 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 the applicable offering period. The first six month offering period under the ESPP commenced on January 1, 2020 and ended on June 30, 2020 and the second offering period commenced on July 1, 2020 and is expected to end on December 31, 2020. A total of 4,427 shares of common stock were purchased pursuant to the ESPP during the nine months ended September 30, 2020 for total proceeds of $75,000. As of September 30, 2020, there were 358,651 shares of common stock available for issuance under the ESPP. The Company recorded share-based compensation for the periods indicated as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Research and development $ 359 $ 34 $ 848 $ 54 General and administrative 795 78 1,709 169 Total share-based compensation $ 1,154 $ 112 $ 2,557 $ 223 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: Nine Months Ended September 30, 2020 2019 Stock Options Expected term (years) 4.00-6.11 5.88-6.11 Expected volatility 86.4-93.7 % 61.8-72.5 % Risk-free interest rate 0.2-1.5 % 1.6-2.6 % Expected dividend — — The following table summarizes stock option activity for the nine months ended September 30, 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 609,000 30.29 Exercised (13,403 ) 2.68 Cancelled (40,482 ) 2.87 Balance outstanding as of September 30, 2020 1,875,358 12.08 8.80 $ 28,652 Exercisable as of September 30, 2020 492,557 $ 2.24 8.32 $ 11,537 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 in subsequent closings.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 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: Nine Months Ended September 30, 2020 2019 Stock options to purchase common stock 1,260,943 1,251,885 Employee stock purchase plan 2,093 — Convertible preferred stock, as converted — 7,077,366 Total 1,263,036 8,329,251

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Related Party Transactions	9. Related Party Transactions 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 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 7).

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 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.
Investments	Investments 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. Generally, investments with original maturities beyond three months at the date of purchase are classified as short-term because it is management’s intent to use the investments to fund current operations or to make them available for current operations. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. The Company periodically evaluates whether declines in fair values of its available-for-sale securities below their book value are other-than-temporary. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the available-for-sale security until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale securities before recovery of its amortized cost basis. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in other expenses, net. The cost of investments sold is based on the specific-identification method. There were no realized gains or losses on investments for the periods presented. Interest on available-for-sale securities is included in other expenses, net and was not material for all periods presented.
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 the 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.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market funds and commercial paper that are stated at fair value.
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 expenses, 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 a subsequent 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 Due to the ongoing COVID-19 pandemic, the Company may experience disruptions that could negatively impact the Company’s growth, employee productivity and its ability to recruit and onboard new employees. The pandemic has disrupted and may continue to disrupt the Company’s business and delay its preclinical and clinical programs and timelines. The extent to which the COVID-19 pandemic may impact the Company’s future operating results and financial condition is uncertain.
Comprehensive Loss	Comprehensive Loss The Company’s comprehensive loss is comprised of changes in unrealized gains (losses) on available-for-sale securities and foreign currency transaction adjustments.
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
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02— Leases In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on Recurring Basis	The following table presents the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy as of September 30, 2020 (in thousands): September 30, 2020 Valuation Amortized Unrealized Unrealized Hierarchy Cost Gains Losses Fair Value Money market funds Level 1 $ 32,445 $ — $ — $ 32,445 Commercial paper Level 2 45,034 1 (1 ) 45,034 Agency bonds Level 2 28,751 12 (3 ) 28,760 U.S. government bonds Level 2 7,135 1 — 7,136 Corporate debt securities Level 2 5,822 — (3 ) 5,819 U.S. treasury bills Level 2 2,150 — — 2,150 Agency discount securities Level 2 460 — — 460 Municipal bonds Level 2 177 — — 177 Total cash equivalents and available-for-sale securities $ 121,974 $ 14 $ (7 ) $ 121,981 Classified as: Cash equivalents $ 44,379 Short-term investments 77,602 Total cash equivalents and available-for-sale securities $ 121,981
Schedule of Contractual Maturities of Available-for-Sale Securities	The following table summarizes the Company’s available-for-sale securities by contractual maturity as of September 30, 2020 (in thousands): September 30, 2020 Within one year $ 103,643 After one year through two years 18,338 Total cash equivalents and available-for-sale securities $ 121,981
Summary of Changes in Fair Value of Level 3 Liability	For the nine months ended September 30, 2019, changes in the fair value of the Company’s Level 3 financial liability were measured on a recurring basis as follows (in thousands): Nine Months Ended September 30, 2019 Beginning balance $ 1,671 Revaluation of convertible preferred stock liability recorded in other expenses, net 21,018 Partial settlement of convertible preferred stock liability in subsequent closings (6,673 ) Ending balance $ 16,016
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: Nine Months Ended September 30, 2019 Stock price $ 0.99 - 1.97 Exercise price $ 1.00 Expected term (years) 0.00 - 2.25 Expected volatility 72.0 % Risk-free interest rate 0.0 - 2.4 %

Consolidated Balance Sheet Co_2

Consolidated Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2020
Balance Sheet Related Disclosures [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): September 30, December 31, 2020 2019 Accrued research and development expense $ 2,602 $ 2,326 Accrued employee and related expenses 1,679 1,396 Accrued professional and legal fees 769 573 Accrued other 288 325 Total accrued expenses $ 5,338 $ 4,620

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Obligations	Future minimum September 30, 2020 Remainder of 2020 $ 64 2021 232 2022 8 Total future minimum annual payments $ 304

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Summary of Share-Based Compensation	The Company recorded share-based compensation for the periods indicated as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2020 2019 2020 2019 Research and development $ 359 $ 34 $ 848 $ 54 General and administrative 795 78 1,709 169 Total share-based compensation $ 1,154 $ 112 $ 2,557 $ 223
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: Nine Months Ended September 30, 2020 2019 Stock Options Expected term (years) 4.00-6.11 5.88-6.11 Expected volatility 86.4-93.7 % 61.8-72.5 % Risk-free interest rate 0.2-1.5 % 1.6-2.6 % Expected dividend — —
Summary of Stock Option Activity	The following table summarizes stock option activity for the nine months ended September 30, 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 609,000 30.29 Exercised (13,403 ) 2.68 Cancelled (40,482 ) 2.87 Balance outstanding as of September 30, 2020 1,875,358 12.08 8.80 $ 28,652 Exercisable as of September 30, 2020 492,557 $ 2.24 8.32 $ 11,537

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of Outstanding Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss	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: Nine Months Ended September 30, 2020 2019 Stock options to purchase common stock 1,260,943 1,251,885 Employee stock purchase plan 2,093 — Convertible preferred stock, as converted — 7,077,366 Total 1,263,036 8,329,251

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands	Nov. 13, 2019USD ($)$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares	Jul. 31, 2020USD ($)$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares	Sep. 30, 2020USD ($)$ / shares	Sep. 30, 2019USD ($)
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%
Proceeds from issuance of common stock, net of underwriters discount and commissions						$ 11
Reverse stock split conversion ratio	0.160849
Cash equivalents and short-term investments		$ 219,200		$ 219,200	$ 219,200
Common Stock
Subsidiary Sale Of Stock [Line Items]
Convertible preferred stock automatically converted into common stock | shares	7,077,366
Public Offerings | Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold | shares	6,100,390			6,072,040
IPO price per share | $ / shares	$ 16
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		397,440
Underwritten public offering | Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold | shares		3,025,000	3,047,040
IPO price per share | $ / shares		$ 28	$ 27.50	$ 28	$ 28
Proceeds from issuance of common stock, net of underwriters discount and commissions		$ 79,500	$ 78,200
Payment of underwriting discounts, commissions		4,600	5,000
Other offering expenses		600	600
Gross proceeds from issue of common stock		$ 84,700	$ 83,800

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	9 Months Ended
	Sep. 30, 2020USD ($)
Accounting Policies [Abstract]
Realized gains or losses on investments	$ 0
Capital contribution by the preferred stockholders	$ 25,600,000
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201813Member
Change in Accounting Principle, Accounting Standards Update, Adopted	true
Change In Accounting Principle Accounting Standards Update Adoption Date	Jan. 1, 2020
Change In Accounting Principle Accounting Standards Update Immaterial Effect	false

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) $ in Thousands	Sep. 30, 2020USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	$ 121,981
Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	121,974
Short-term investments, Gross Unrealized Holding Gains	14
Short-term investments, Gross Unrealized Holding Losses	(7)
Short-term investments, Aggregated Fair Value	121,981
Recurring | Cash equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	44,379
Recurring | Short-term investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	77,602
Recurring | Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	32,445
Short-term investments, Aggregated Fair Value	32,445
Recurring | Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	45,034
Short-term investments, Gross Unrealized Holding Gains	1
Short-term investments, Gross Unrealized Holding Losses	(1)
Short-term investments, Aggregated Fair Value	45,034
Recurring | Level 2 | Agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	28,751
Short-term investments, Gross Unrealized Holding Gains	12
Short-term investments, Gross Unrealized Holding Losses	(3)
Short-term investments, Aggregated Fair Value	28,760
Recurring | Level 2 | Corporate Debt
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	5,822
Short-term investments, Gross Unrealized Holding Losses	(3)
Short-term investments, Aggregated Fair Value	5,819
Recurring | Level 2 | U.S. government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	7,135
Short-term investments, Gross Unrealized Holding Gains	1
Short-term investments, Aggregated Fair Value	7,136
Recurring | Level 2 | U.S. treasury bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	2,150
Short-term investments, Aggregated Fair Value	2,150
Recurring | Level 2 | Agency discount securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	460
Short-term investments, Aggregated Fair Value	460
Recurring | Level 2 | Municipal Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	177
Short-term investments, Aggregated Fair Value	$ 177

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Contractual Maturities of Available-for-Sale Securities (Details) $ in Thousands	Sep. 30, 2020USD ($)
Fair Value Disclosures [Abstract]
Within one year	$ 103,643
After one year through two years	18,338
Total cash equivalents and available-for-sale securities	$ 121,981

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, financial assets		$ 0
Level 3
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, financial liability	$ 0

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Changes in Fair Value of Level 3 Liability (Details) - Recurring - Level 3 $ in Thousands	9 Months Ended
	Sep. 30, 2019USD ($)
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 expenses, net	21,018
Partial settlement of convertible preferred stock liability in subsequent closings	(6,673)
Ending balance	$ 16,016

Fair Value Measurements - Sum_3

Fair Value Measurements - Summary of Fair Value Assumptions (Details) - Convertible Preferred Stock Liability - Black Scholes Option Pricing Model	9 Months Ended
	Sep. 30, 2019$ / shares
Stock Price | Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	0.99
Stock Price | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	1.97
Exercise Price
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	1
Expected Term (Years) | Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	0 years
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
Risk-free Interest Rate | Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	0
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 Co_3

Consolidated Balance Sheet Components - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued research and development expense	$ 2,602	$ 2,326
Accrued employee and related expenses	1,679	1,396
Accrued professional and legal fees	769	573
Accrued other	288	325
Total accrued expenses	$ 5,338	$ 4,620

Commitments and Contingencies -

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Obligations (Details) $ in Thousands	Sep. 30, 2020USD ($)
Commitments And Contingencies Disclosure [Abstract]
Remainder of 2020	$ 64
2021	232
2022	8
Total future minimum annual payments	$ 304

Commitments and Contingencies_2

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Apr. 30, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Loss Contingencies [Line Items]
Operating leases, rent expense		$ 61,000	$ 48,000	$ 208,000	$ 108,000
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	$ 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

Term Loan - Additional Informat

Term Loan - Additional Information (Details) - Loan Agreement	Apr. 07, 2020USD ($)$ / sharesshares	Sep. 30, 2020USD ($)	Jul. 31, 2020
Debt Instrument [Line Items]
Credit facility maturity date	Sep. 1, 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 loans 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%.
Warrant expiration date	Apr. 7, 2030		Jun. 30, 2025
Debt issuance costs, gross	$ 600,000	$ 600,000
Debt issuance costs		200,000
Dividends
Debt Instrument [Line Items]
Fair value of warrant assumptions, dividends	$ 0
Black Scholes Option Pricing Model | Risk-free Interest Rate
Debt Instrument [Line Items]
Fair Measurement Input	0.0075
Black Scholes Option Pricing Model | Expected Volatility
Debt Instrument [Line Items]
Fair Measurement Input	0.9230
Black Scholes Option Pricing Model | Expected Term (Years)
Debt Instrument [Line Items]
Fair Measurement Input	10 years
Prime Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.25%
Minimum
Debt Instrument [Line Items]
Debt instrument, interest rate	4.50%
Term A Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 10,000,000
Credit facility maturity date	Nov. 1, 2022
Amount drawn		0
Warrants to purchase common stock | shares	25,000
Warrant exercise price | $ / shares	$ 22.06
Term B Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 5,000,000
Amount drawn		$ 0
Warrants to purchase common stock | shares	8,333

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	Nov. 13, 2019	Oct. 31, 2019	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Apr. 30, 2018
Stockholders' Equity [Line Items]
Proceeds from issuance of common stock					$ 11,000
Capital contribution related to extinguishment of preferred stock liability	$ 25,600,000
Common Stock
Stockholders' Equity [Line Items]
Convertible preferred stock automatically converted into common stock	7,077,366
Series A Convertible Preferred Stock
Stockholders' Equity [Line Items]
Number of shares committed to purchase, no longer issuable	16,000,000
Series A Share Purchase Agreement | Series A Convertible Preferred Stock
Stockholders' Equity [Line Items]
Per share price of issuance of shares						$ 1
Employee Stock Purchase Plan
Stockholders' Equity [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%
Second offering period		6 months
Commencement date of second six month offering period		Jul. 1, 2020
First offering period		6 months
Common stock issued		4,427
Proceeds from issuance of common stock				$ 75,000
Commencement date of first six month offering period		Jan. 1, 2020
Number of shares of common stock available for issuance under ESPP				358,651
2019 Plan
Stockholders' Equity [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				1,506,991
Maximum | Series A Share Purchase Agreement | Series A Convertible Preferred Stock
Stockholders' Equity [Line Items]
Total amount of preferred shares issuable by the entity						$ 60,000,000
Maximum | Employee Stock Purchase Plan
Stockholders' Equity [Line Items]
Period for increase in number of shares of common stock reserved for issuance		10 years
Maximum | 2019 Plan
Stockholders' Equity [Line Items]
Period for increase in number of shares of common stock reserved for issuance				10 years

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Share-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	$ 1,154	$ 112	$ 2,557	$ 223
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	359	34	848	54
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	$ 795	$ 78	$ 1,709	$ 169

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Estimated Fair Value of Option Awards Granted Using Black-Scholes Option-Pricing Model (Details) - Stock Options	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	0.20%	1.60%
Risk-free interest rate, maximum	1.50%	2.60%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	4 years	5 years 10 months 17 days
Expected volatility	86.40%	61.80%
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 1 month 9 days	6 years 1 month 9 days
Expected volatility	92.70%	72.50%

Stockholders' Equity - Summar_3

Stockholders' Equity - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares
Number of Options
Outstanding, Beginning Balance | shares	1,320,243
Granted | shares	609,000
Exercised | shares	(13,403)
Cancelled | shares	(40,482)
Outstanding, Ending Balance | shares	1,875,358	1,320,243
Exercisable as of September 30, 2020 | shares	492,557
Weighted Average Exercise Price
Weighted Average Exercise Price Outstanding, Beginning Balance | $ / shares	$ 3.34
Weighted Average Exercise Price, Granted | $ / shares	30.29
Weighted Average Exercise Price, Exercised | $ / shares	2.68
Weighted Average Exercise Price, Cancelled | $ / shares	2.87
Weighted Average Exercise Price Outstanding, Ending Balance | $ / shares	12.08	$ 3.34
Weighted Average Exercise Price, Exercisable as of September 30, 2020 | $ / shares	$ 2.24
Weighted Average Remaining Contractual Term (In years)
Weighted Average Remaining Contractual Term (In years), Outstanding	8 years 9 months 18 days	9 years 2 months 23 days
Weighted Average Remaining Contractual Term (In years), Exercisable as of September 30, 2020	8 years 3 months 25 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value Outstanding | $	$ 28,652	$ 30,353
Aggregate Intrinsic Value, Exercisable as of September 30, 2020 | $	$ 11,537

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Outstanding Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss (Details) - shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 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	1,263,036	8,329,251
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	1,260,943	1,251,885
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	2,093
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		7,077,366

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) $ in Millions	Nov. 13, 2019USD ($)shares
Related Party Transaction [Line Items]
Capital contribution	$ 25.6
Series A Convertible Preferred Stock
Related Party Transaction [Line Items]
Number of shares committed to purchase, no longer issuable | shares	16,000,000
Additional Paid-in Capital
Related Party Transaction [Line Items]
Capital contribution	$ 25.6