Mirum Pharmaceuticals (MIRM) 10-K 9 Mar 21 2020 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 05, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Registrant Name	Mirum Pharmaceuticals, Inc.
Entity Central Index Key	0001759425
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Interactive Data Current	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
ICFR Auditor Attestation Flag	false
Entity Public Float			$ 243,500,000
Entity Common Stock, Shares Outstanding		30,419,707
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity File Number	001-38981
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	83-1281555
Entity Address, Address Line One	950 Tower Lane, Suite 1050,
Entity Address, City or Town	Foster City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94404
City Area Code	650
Local Phone Number	667-4085
Document Transition Report	false
Document Annual Report	true
Title of 12(b) Security	Common stock, par value $0.0001 per share
Trading Symbol	MIRM
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the Registrant’s definitive proxy statement for its 2021 Annual Meeting of Stockholders, which the Registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the Registrant’s fiscal year ended December 31, 2020, are incorporated by reference into Part III of this Annual Report on Form 10-K.

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 142,086	$ 11,970
Short-term investments	89,734	104,690
Prepaid expenses and other current assets	4,530	2,703
Total current assets	236,350	119,363
Long-term investments	0	23,292
Property and equipment, net	1,293	1,372
Operating lease right-of-use assets	1,949	2,361
Other assets	1,272	324
Total assets	240,864	146,712
Current liabilities:
Accounts payable	3,151	3,351
Accrued expenses	13,411	9,328
Operating lease liabilities	636	397
Derivative liability	1,264	0
Total current liabilities	18,462	13,076
Revenue interest liability, net	47,651	0
Operating lease liabilities, noncurrent	2,627	3,251
Other liabilities	29	36
Total liabilities	68,769	16,363
Commitments and contingencies	0	0
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized as of December 31, 2020 and 2019, respectively; zero shares issued and outstanding as of December 31, 2020 and 2019, respectively; and liquidation value of $0 as of December 31, 2020 and 2019, respectively	0	0
Common stock, $0.0001 par value; 200,000,000 shares authorized as of December 31, 2020 and 2019, respectively; 30,032,600 shares issued and 29,776,544 shares outstanding, excluding 256,056 shares subject to repurchase as of December 31, 2020; and 22,989,987 shares issued and 22,600,338 shares outstanding, excluding 389,649 shares subject to repurchase as of December 31, 2019	3	2
Additional paid-in capital	345,180	200,119
Accumulated deficit	(173,171)	(69,901)
Accumulated other comprehensive income	83	129
Total stockholders’ equity	172,095	130,349
Total liabilities and stockholders’ equity	$ 240,864	$ 146,712

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares, issued	0	0
Preferred stock, shares, outstanding	0	0
Preferred stock, liquidation preference	$ 0	$ 0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares, issued	30,032,600	22,989,987
Common stock, shares, outstanding	29,776,544	22,600,338
Common stock, subject to repurchase	256,056	389,649

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating expenses:
Research and development	$ 81,605	$ 42,991
General and administrative	22,691	11,752
Total operating expenses	104,296	54,743
Loss from operations	(104,296)	(54,743)
Other income (expense):
Interest income	1,559	2,232
Interest expense	(335)	0
Other expense, net	(192)	(21)
Net loss before provision for income taxes	(103,264)	(52,532)
Provision for income taxes	6	21
Net loss	$ (103,270)	$ (52,553)
Net loss per share, basic and diluted	$ (4.09)	$ (4.58)
Weighted-average shares of common stock outstanding, basic and diluted	25,251,968	11,486,367

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (103,270)	$ (52,553)
Other comprehensive gain (loss):
Unrealized (loss) gain on available-for-sale investments	(75)	156
Cumulative translation adjustments	29	(27)
Comprehensive loss	$ (103,316)	$ (52,424)

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock, Redeemable Common Stock and Stock Holders' Equity (Deficit) - USD ($) $ in Thousands	Total	Revenue Interest Purchase Agreement	Underwritten Public Offerings	At-the-market Offering	Redeemable Convertible Preferred Stock	Redeemable Common Stock	Common Stock	Common StockRevenue Interest Purchase Agreement	Common StockUnderwritten Public Offerings	Common StockAt-the-market Offering	Additional Paid-In Capital	Additional Paid-In CapitalRevenue Interest Purchase Agreement	Additional Paid-In CapitalUnderwritten Public Offerings	Additional Paid-In CapitalAt-the-market Offering	Accumulated Deficit	Accumulated Other Comprehensive Income
Balance at Dec. 31, 2018					$ 59,849	$ 6,990
Balance, Shares at Dec. 31, 2018					59,908,284	1,859,151
Balance at Dec. 31, 2018	$ (17,313)						$ 1				$ 34				$ (17,348)
Balance, Shares at Dec. 31, 2018							636,719
Issuance of common stock	67,200										67,200
Issuance of common stock, Shares							5,000,000
Issuance of Series A redeemable convertible preferred stock, net of issuance costs, Shares					59,844,699
Issuance of Series A redeemable convertible preferred stock, net of issuance costs					$ 59,977
Conversion of Series A redeemable convertible preferred stock into common stock on initial public offering	119,826				$ (119,826)		$ 1				119,825
Conversion of Series A redeemable convertible preferred stock into common stock on initial public offering, Shares					(119,752,983)		14,969,118
Reclassification of redeemable common stock into common stock on initial public offering	6,990					$ (6,990)					6,990
Reclassification of redeemable common stock into common stock on initial public offering, Shares						(1,859,151)	1,859,151
Restricted common stock vested in the period, Shares							135,350
Stock-based compensation	6,070										6,070
Net loss	(52,553)														(52,553)
Other comprehensive income (loss)	129															$ 129
Balance at Dec. 31, 2019	130,349						$ 2				200,119				(69,901)	129
Balance, Shares at Dec. 31, 2019							22,600,338
Issuance of common stock		$ 10,766	$ 114,679	$ 6,279					$ 1			$ 10,766	$ 114,678	$ 6,279
Issuance of common stock, Shares								509,164	6,150,000	305,969
Issuance of common stock in connection with common stock option exercises	328										328
Issuance of common stock in connection with common stock option exercises, Shares							47,604
Issuance of common stock in connection with Employee Stock Purchase Plan	456										456
Issuance of common stock in connection with Employee Stock Purchase Plan, Shares							29,876
Restricted common stock vested in the period, Shares							133,593
Stock-based compensation	12,554										12,554
Net loss	(103,270)														(103,270)
Other comprehensive income (loss)	(46)															(46)
Balance at Dec. 31, 2020	$ 172,095						$ 3				$ 345,180				$ (173,171)	$ 83
Balance, Shares at Dec. 31, 2020							29,776,544

Consolidated Statements of Re_2

Consolidated Statements of Redeemable Convertible Preferred Stock, Redeemable Common Stock and Stock Holders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Redeemable Convertible Preferred Stock
Issuance of stock at per share		$ 1.00259507
Issuance of Series A redeemable convertible preferred stock, issuance costs		$ 23
Common Stock
Issuance costs		$ 7,800
Common Stock | Underwritten Public Offerings
Issuance costs	$ 8,322
Common Stock | At-the-market Offering
Issuance costs	$ 314

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating activities
Net loss	$ (103,270)	$ (52,553)
Reconciliation of net loss to net cash used in operating activities:
Stock-based compensation	12,554	6,070
Depreciation and amortization	305	139
Amortization of operating lease right-of-use assets	318	185
Non-cash interest expense related to the revenue interest liability	335	0
Net amortization (accretion) on investments	72	(326)
Change in operating assets and liabilities:
Prepaid and other current assets	(1,827)	(2,691)
Operating lease right-of-use assets	94	(33)
Other assets	(954)	(160)
Accounts payable, accrued expenses and other liabilities	3,683	10,058
Operating lease liabilities	(385)	(51)
Net cash used in operating activities	(89,075)	(39,362)
Investing activities
Proceeds from maturities of investments	85,900	24,500
Proceeds from paydown of investments	26,761	0
Purchase of investments	(74,562)	(152,000)
Purchase of property and equipment	(225)	(281)
Net cash provided by (used in) investing activities	37,874	(127,781)
Financing activities
Proceeds from the issuance of Series A redeemable convertible preferred stock, net of issuance costs	0	59,977
Proceeds from issuance of common stock in public offerings, net of issuance costs	121,087	67,200
Proceeds from issuance of common stock in private placement, net of issuance costs	10,000	0
Proceeds from issuance of common stock pursuant to equity award plans	784	0
Proceeds from revenue interest liability, net of issuance costs	49,575	0
Payment of deferred offering costs in connection with the shelf registration and sales agreement	(158)	0
Net cash provided by financing activities	181,288	127,177
Effect of exchange rate on cash and cash equivalents	29	(27)
Net increase (decrease) in cash and cash equivalents	130,116	(39,993)
Cash and cash equivalents at beginning of period	11,970	51,963
Cash and cash equivalents at end of period	142,086	11,970
Supplemental disclosure of cash flow information:
Cash paid for income taxes	11	21
Operating cash flows paid for operating lease	576	170
Noncash investing and financing activities:
Revenue interest liability issuance costs included in accrued liabilities	229	0
Deferred offering costs included in accrued liabilities	129	164
Compound derivative liability related to revenue interest liability	1,264	0
Operating lease right-of-use asset obtained in exchange for operating lease liability	0	3,700
Landlord paid tenant improvements	0	1,231
Conversion of Series A redeemable convertible preferred stock into common stock on initial public offering	0	119,826
Reclassification of redeemable common stock into common stock on initial public offering	$ 0	$ 6,990

Organization and Description of

Organization and Description of Business	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of Business	1. Organization and Description of Business Mirum Pharmaceuticals, Inc. (the “Company”) was incorporated in the State of Delaware on May 2, 2018, and is headquartered in Foster City, California. The Company is a biopharmaceutical company focused on the development and commercialization of a late-stage pipeline of novel therapies for debilitating liver diseases. The Company’s pipeline consists of two clinical-stage product candidates, maralixibat and volixibat, with mechanisms of action that have potential utility across a wide range of orphan liver diseases. The Company commenced significant operations in November 2018. The consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, Mirum Pharmaceuticals AG. All intercompany balances and transactions among the consolidated entities have been eliminated in consolidation. The Company views its operations and manages its business as one operating segment. Reverse Stock Split In July 2019, the Company effected a 1-for-8 reverse stock split of its common stock. The par value and the authorized number of shares of common stock were not adjusted as a result of the reverse stock split. The reverse stock split resulted in an adjustment to the conversion price of the Company’s Series A redeemable convertible preferred stock (the “Series A Preferred Stock”) to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion. The accompanying consolidated financial statements and notes to the consolidated financial statements give retroactive effect to the reverse stock split for all periods presented. Liquidity The Company has a limited operating history, has incurred significant operating losses since its inception, and the revenue and income potential of the Company’s business and market are unproven. As of December 31, 2020, the Company had an accumulated deficit of $173.2 million and cash, cash equivalents and investments of $231.8 million, which are available to fund future operations. The Company believes that its cash, cash equivalents and investments as of December 31, 2020 provide sufficient capital resources to continue its operations for at least twelve months from the issuance date of the accompanying consolidated financial statements. T he consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the normal course of business. The consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Use of Estimates The preparation of consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to the revenue interest liability, accrued research and development expenses, the valuation of derivative liabilities and the valuation allowance of deferred tax assets resulting from net operating losses. These estimates and assumptions are based upon historical experience, knowledge of current events and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results could differ materially from those estimates. In December 2019, a novel strain of coronavirus, which causes COVID-19, was identified. Due to the rapid and global spread of the virus, on March 11, 2020, the World Health Organization declared the COVID-19 outbreak a pandemic. To slow the proliferation of COVID-19, governments have implemented extraordinary measures, which include the mandatory closure of businesses, restrictions on travel and gatherings, and quarantine and physical distancing requirements. There were no significant estimates contained in the preparation of the Company’s consolidated financial statements or impacts to the Company’s consolidated financial statements for the year ended December 31, 2020 that were directly a result of the COVID-19 pandemic. The Company is not aware of any specific event or circumstance that would require an update to its estimates, judgments and assumptions or a revision of the carrying value of the Company’s assets or liabilities as of the date of this filing. Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents. The carrying amounts reported in the consolidated balance sheets for cash and cash equivalents are valued at cost, which approximate their fair value. Cash equivalents may consist of money market accounts, money market funds, U.S. treasury bills and repurchase agreements. Concentrations of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents, and short and long-term investments. The Company minimizes the amount of credit exposure by investing cash that is not required for immediate operating needs in money market funds, government obligations and/or commercial paper with short maturities. To date, the Company has not experienced any losses associated with this credit risk and continues to believe that this exposure is not significant. Investments The Company classifies all investments as available-for-sale, as the sale of such securities may be required prior to maturity . Management determines the appropriate classification of its investments in debt securities at the time of purchase. Investments with original maturities beyond three months at the date of purchase and which mature at, or less than twelve months from the balance sheet date, are classified as a current asset. Investments are recorded at fair value, with unrealized gains and losses reported as accumulated other comprehensive income (loss) until realized . 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. To date, the Company has not identified any other than temporary declines in fair value of its investments. Fair Value of Financial Instruments The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets; Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. The carrying amounts of all cash equivalents, accounts payable and accrued liabilities are reasonable estimates of their fair value. Property and Equipment Property and equipment are recorded at cost less accumulated depreciation. Depreciation is computed on a straight-line basis over the estimated useful lives of the related assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of their useful lives or the related lease term. Impairment of Long-Lived Assets Long -lived assets are reviewed for indications of possible impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amounts to the future undiscounted cash flows attributable to these assets. An impairment loss is recognized to the extent an asset group is not recoverable, and the carrying amount exceeds the projected discounted future cash flows arising from these assets. There were no impairments of long-lived assets for any of the periods presented. Deferred Offering Costs Deferred offering costs directly related to the Company’s shelf registration and sales agreement primarily consisted of legal, accounting, printing and SEC filing fees. These costs are reclassified to additional paid-in capital on a pro-rata basis as the Company completes offerings under the shelf registration, with any remaining deferred costs to be charged to results of operations at the end of the three-year life of the shelf registration. During the year ended December 31, 2020, the deferred offering costs reclassified to additional paid-in capital as a result of the transactions contemplated under a shelf registration were $59,000. Accrued Research and Development Expenses The Company accrues and expenses clinical trial activities performed by third parties based upon estimates of the proportion of work completed over the life of the individual study and patient enrollment rates in accordance with agreements established with clinical research organizations and clinical trial sites. The Company determines the estimates by reviewing contracts, vendor agreements and purchase orders and through discussions with internal clinical personnel and external service providers as to the progress or stage of completion of trials or services and the agreed-upon fee to be paid for such services. The Company makes estimates of accrued expenses as of each balance sheet date based on facts and circumstances known to the Company at that time. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. The Company has not experienced any material differences between accrued costs and actual costs incurred for the periods presented. Nonrefundable advance payments for goods and services are deferred and recognized as expense in the period that the related goods are consumed or services are performed. Revenue Interest Liability, Net The revenue interest liability, net, associated with the Revenue Interest Purchase Agreement (“RIPA”) that the Company entered into in December 2020 A significant increase or decrease in net sales will materially impact the revenue interest liability, interest expense and the time period for repayment. Derivative Liability The RIPA contains certain features that meet the definition of being embedded derivatives requiring bifurcation as a separate compound financial instrument apart from the RIPA. The derivative liability is initially measured at fair value on issuance and is subject to remeasurement at each reporting period with changes in fair value recognized as other income (expense) in the consolidated statements of operations as the change in fair value of derivative liability. Research and Development Expenses Research and development expenses consist primarily of fees paid to contract research organizations and other vendors for clinical, non-clinical and manufacturing services, salaries and benefits, including stock-based compensation, consultant expenses, costs related to acquiring manufacturing materials, costs related to compliance with regulatory requirements and license payments related to acquiring intellectual property rights for the Company’s product candidates. Research and development expenses are expensed as incurred. Leases The Company determines if a contractual arrangement is or contains a lease at inception. Operating lease right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset during the lease term, and operating lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating leases are included in ROU assets, current operating lease liabilities, and long-term operating lease liabilities on the accompanying consolidated balance sheets. Operating lease ROU assets and lease liabilities are initially recognized based on the present value of the future minimum lease payments over the lease term at commencement date calculated using the Company’s incremental borrowing rate applicable to the lease asset, unless the implicit rate is readily determinable. Operating lease ROU assets also include any lease payments made at or before lease commencement and exclude any lease incentives received. The Company determines the lease term as the noncancelable period of the lease and may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Leases with a term of 12 months or less are not recognized on the consolidated balance sheet. The Company’s leases do not contain any residual value guarantees. Lease expense for minimum lease payments is recognized as rent expense on a straight-line basis over the lease term. Stock-Based Compensation The Company recognizes stock-based compensation for all stock-based awards to employees based on the grant-date fair value of the award. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model, and the assumptions used in calculating the fair value of stock-based awards represent management’s estimates and involve inherent uncertainties and the application of management’s judgment. The fair value of equity awards that are expected to vest is amortized on a straight-line basis over the requisite service period. Stock-based compensation is recognized net of actual forfeitures when they occur. Income Taxes Income taxes are recorded using the liability method, under which deferred tax assets and liabilities are determined based on differences between financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Valuation allowances are recorded against deferred tax assets when it is determined it is more-likely-than-not that some or all of the tax benefits will not be realized. The Company accounts for uncertain tax positions in accordance with the provisions of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification No. 740, Income Taxes Interest and penalties related to unrecognized tax benefits, if any, are recorded as a component of income tax expense. Net Loss Per Share Basic net loss per share is computed by dividing net loss attributable to common stockholders by the weighted-average shares of common stock outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average shares of common stock and potentially dilutive securities outstanding for the period determined using the treasury-stock and if-converted methods. Diluted net loss per share excludes the potential impact of the Company’s common stock subject to repurchase, common stock options, contingently issuable employee stock purchase plan shares and contingently issuable overallotment shares because their effect would be anti-dilutive due to the Company’s net loss. Since the Company incurred a net loss in each of the periods presented, basic and diluted net loss per share were the same. The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: December 31, 2020 2019 Options to purchase common stock 5,071,740 3,366,812 Common stock subject to repurchase 256,056 389,649 Employee stock purchase plan contingently issuable 12,931 — Overallotment shares contingently issuable 562,500 — Total 5,903,227 3,756,461 Recently Adopted Accounting Pronouncements On January 1, 2020, the Company adopted Accounting Standards Update (“ASU”) No. 2018-13, Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement (Topic 820) In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes (Topic 740) . The guidance eliminates certain exceptions for recognizing deferred taxes for investments, performing intraperiod allocation and calculating income taxes in interim periods. This guidance also includes guidance to reduce complexity in certain areas, including recognizing deferred taxes for tax goodwill and allocating taxes to members of a consolidated group. ASU 2019-12 is effective for annual and interim periods in fiscal years beginning after December 15, 2020. Early adoption is permitted. The Company early adopted this guidance in the fourth quarter of 2020. The adoption did not have a material impact on the Company’s consolidated financial statements. Other recent accounting pronouncements issued by the FASB (including its Emerging Issues Task Force), the American Institute of Certified Public Accountants, and the Securities and Exchange Commission (“SEC”) did not, or are not believed by management to, have a material impact on the Company’s consolidated financial position, results of operations or cash flows . Recent Accounting Pronouncements Not Yet Adopted In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instruments - Credit Losses Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Derivatives and Hedging (Topic 815), and Financial Instruments (Topic 842), Codification Improvements to Financial Instruments is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019 for public business entities, excluding smaller reporting companies. In August Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging-Contracts in Entity’s Own Equity (Subtopic 815-40) The Company is currently evaluating the impact this change will have on its consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements by major security type are presented in the following table (in thousands): December 31, 2020 Level 1 Level 2 Level 3 Total Financial assets: Money market fund $ 127,783 $ — $ — $ 127,783 U.S. treasury bills 29,997 — — 29,997 Corporate debt securities — 23,201 — 23,201 Commercial paper — 41,460 — 41,460 U.S. government bonds — 5,066 — 5,066 Asset-backed securities — 2,006 — 2,006 Total financial assets $ 157,780 $ 71,733 $ — $ 229,513 Financial liabilities: Derivative liability — — 1,264 1,264 Total financial liabilities $ — $ — $ 1,264 $ 1,264 December 31, 2019 Level 1 Level 2 Level 3 Total Financial assets: Money market fund $ 10,621 $ — $ — $ 10,621 Corporate debt securities — 41,668 — 41,668 Commercial paper — 35,016 — 35,016 U.S. government bonds — 22,511 — 22,511 Asset-backed securities — 28,787 — 28,787 Total $ 10,621 $ 127,982 $ — $ 138,603 The carrying amounts of certain financial instruments such as cash and cash equivalents, prepaid expenses, other current assets, accounts payable, accrued expenses, and other current liabilities as of December 31, 2020 and December 31, 2019 approximate their related fair values due to the short-term maturities of these instruments. Derivative Liability The debt pursuant to the RIPA contains embedded derivatives requiring bifurcation as a single compound derivative instrument. The Company estimated the fair value of the derivative liability on issuance and at December 31, 2020 using a “with-and-without” method. The “with-and-without” methodology involves valuing the whole instrument on an as-is basis and then valuing the instrument without the individual embedded derivative. The difference between the entire instrument with the embedded derivative compared to the instrument without the embedded derivative was the fair value of the derivative liability on issuance and at December 31, 2020. The estimated probability and timing of underlying events triggering the exercisability of the put options contained within the RIPA, forecasted cash flows and the discount rate are significant unobservable inputs used to determine the estimated fair value of the entire instrument with the embedded derivative. As of the inception date and December 31, 2020, the discount rate used for valuation to the derivative liability is 15.9%. The following table provides a summary of the change in the estimated fair value of the Company’s derivative liability, classified as Level 3 in the fair value hierarchy: Balance at January 1, 2020 $ — Initial fair value of derivative liability 1,264 Balance at December 31, 2020 $ 1,264

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2020
Financial Instruments Owned At Fair Value [Abstract]
Financial Instruments	4. Financial Instruments The fair value and amortized cost of cash equivalents and available-for-sale investments by major security type are presented in the following table (in thousands): December 31, 2020 Amortized Cost Unrealized Gain Unrealized Loss Estimated Fair Value Cash equivalents and investments: Money market fund $ 127,783 — — $ 127,783 U.S. treasury bills 29,995 2 — 29,997 Corporate debt securities 23,126 75 — 23,201 Commercial paper 41,460 — — 41,460 U.S. government bonds 5,067 — (1 ) 5,066 Asset-backed securities 2,001 5 — 2,006 Total cash equivalents and investments $ 229,432 $ 82 $ (1 ) $ 229,513 Classified as: Cash equivalents $ 139,779 Short-term investments 89,734 Total cash equivalents and investments $ 229,513 December 31, 2019 Amortized Cost Unrealized Gain Unrealized Loss Estimated Fair Value Cash equivalents and investments: Money market fund $ 10,621 $ — $ — $ 10,621 Corporate debt securities 41,556 113 (1 ) 41,668 Commercial paper 35,016 — — 35,016 U.S. government bonds 22,492 19 — 22,511 Asset-backed securities 28,762 25 — 28,787 Total cash equivalents and investments $ 138,447 $ 157 $ (1 ) $ 138,603 Classified as: Cash equivalents $ 10,621 Short-term investments 104,690 Long-term investments 23,292 Total cash equivalents and investments $ 138,603 As of December 31, 2020, the remaining contractual maturities of available-for-sale debt securities were less than 12 months. During the years ended December 31, 2020 and 2019, there have been no significant realized gains or losses on available-for-sale investments. During the years ended December 31, 2020 and 2019, no other-than-temporary impairment losses on these securities.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses consist of the following (in thousands): December 31, 2020 2019 Accrued clinical trials 3,673 4,795 Accrued professional service fees 2,157 777 Accrued contract manufacturing and non-clinical costs 2,780 1,540 Accrued compensation and related benefits 4,801 2,216 Total accrued expenses $ 13,411 $ 9,328

Revenue Interest Purchase Agree

Revenue Interest Purchase Agreement	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Revenue Interest Purchase Agreement	6. Revenue Interest Purchase Agreement In December 2020, the Company entered into the RIPA to obtain financing for the commercialization and further development of maralixibat and other working capital needs. The Company may be entitled to receive up to approximately $150.0 million in subsequent installments as follows : As consideration for such payments, the Purchasers have the right to receive certain revenue interests (the “Revenue Interests”) from the Company based on annual net sales of maralixibat, if approved, which will be tiered payments (the “Revenue Interest Payments”) based on whether such annual net sales are (i) less than or equal to $350.0 million (“Tier 1”), (ii) exceeding $350.0 million and less than or equal to $1.1 billion (“Tier 2”), or (iii) exceeding $1.1 billion (“Tier 3”). The Revenue Interest Payments will initially be 9.75% (at Tier 1) and 2.00% (at Tier 2 and Tier 3) of such annual net sales. If the Purchasers have received Revenue Interest Payments in an amount equal to or greater than 110.0% of the total payments actually made by the Purchasers to the Company, exclusive of transaction expenses (the “Cumulative Purchaser Payments”), on or prior to December 31, 2026, the Revenue Interests shall be reduced to 2.00% at Tier 1 and 0.00% at Tier 3 for all subsequent calendar years beginning on January 1, 2027. If the Purchasers have not received Revenue Interest Payments in an amount equal to or greater than 110.0% of the Cumulative Purchaser Payments on or prior to December 31, 2026, the Revenue Interests shall be increased for all subsequent calendar years beginning on January 1, 2027 to a single defined rate (with no separate tiers) that would have provided the Purchasers with an amount equal to 110.0% of the Cumulative Purchaser Payments on or prior to December 31, 2026 had such rate applied to Tier 1 of initial Revenue Interest Payments. The Purchasers’ rights to receive the Revenue Interest Payments shall terminate on the date on which the Purchasers have received Revenue Interest Payments of 195.0% of the Cumulative Purchaser Payments, unless the RIPA is terminated earlier. Under the RIPA, the Company has an option (the “Call Option”) to terminate the RIPA and repurchase future Revenue Interests at any time upon advance written notice. Additionally, the Purchasers have an option (the “Put Option”) to terminate the RIPA and to require the Company to repurchase future Revenue Interests upon enumerated events such as a bankruptcy event, an uncured material breach, a material adverse effect or a change of control, or upon the 12 th In addition, the RIPA contains various representations and warranties, information rights, non-financial covenants, indemnification obligations and other provisions that are customary for a transaction of this nature. The Purchaser’s obligations to fund the scheduled installments are subject to certain customary conditions as set forth in the RIPA. Concurrently with the RIPA, the Company entered into a Common Stock Purchase Agreement (“CSPA”) with certain affiliates of Oberland, pursuant to which the Company sold an aggregate of 509,164 shares of its common stock for an aggregate purchase price of $10.0 million. The $50.0 million received pursuant to the RIPA and $10.0 million received pursuant to the CSPA was allocated between the resulting financial instruments on a relative fair value basis, with $49.2 million allocated to the debt under the RIPA and $10.8 million allocated to the common stock issued under the CSPA. The Put Options under the RIPA that are exercisable by Purchasers upon certain contingent events were determined to be embedded derivatives requiring bifurcation and separately accounted for as a single compound derivative instrument. The Company recorded the initial fair value of the derivative liability of $1.3 million as a debt discount, which will be amortized to interest expense over the expected term of the debt using the effective interest method. In connection with the RIPA, as of December 31, 2020, $47.7 million was recorded as a revenue interest liability on the consolidated balance sheet. The Company imputes interest expense associated with this liability using the effective interest rate method. The effective interest rate is calculated based on the rate that would enable the debt to be repaid in full over the anticipated life of the arrangement. The interest rate on this liability may vary during the term of the agreement depending on a number of factors, including the level of forecasted net sales. The Company evaluates the interest rate quarterly based on its current net sales forecasts utilizing the prospective method. A significant increase or decrease in net sales will materially impact the revenue interest liability, interest expense and the time period for repayment. The Company recorded $0.3 million in interest expense related to this arrangement for the year ended December 31, 2020. The Company incurred $0.7 million of issuance costs in connection with the RIPA, which will be amortized to interest expense over the estimated term of the debt. Revenue Interest Payments made as a result of the Company’s net sales will reduce the revenue interest liability. The following table summarizes the revenue interest liability activity during the year ended December 31, 2020 (in thousands): Revenue interest liability at inception $ 49,234 Interest expense recognized 335 Capitalized issuance costs (654 ) Debt discount from embedded derivatives (1,264 ) Revenue interest liability at December 31, 2020 $ 47,651

Asset Acquisitions

Asset Acquisitions	12 Months Ended
	Dec. 31, 2020
Asset Acquisitions [Abstract]
Asset Acquisitions	7. Asset Acquisitions Assignment and License Agreement with Shire International GmbH (Takeda) In November 2018, the Company entered into an Assignment and License Agreement (the “Shire Agreement”) with Shire International GmbH (“Shire”), which was subsequently acquired by Takeda Pharmaceutical Company Limited, and made an upfront payment to Shire of $7.5 million and issued Shire 1,859,151 shares of redeemable common stock with an estimated fair value of $7.0 million, or $3.76 per share. Under the terms of the Shire Agreement, Shire granted the Company an exclusive, royalty bearing worldwide license to develop and commercialize its two product candidates, maralixibat and volixibat. As part of the Shire Agreement, the Company was assigned license agreements held by Shire with Satiogen Pharmaceuticals, Inc. (“Satiogen”), Pfizer Inc. (“Pfizer”) and Sanofi-Aventis Deutschland GmbH (“Sanofi”). The Company has the right to sublicense under the Shire Agreement and additionally has the right to sublicense under the Satiogen, Pfizer and Sanofi licenses subject to the terms of those license agreements. The Company is obligated to pay Shire up to an aggregate of $109.5 million upon the achievement of certain clinical development and regulatory milestones for maralixibat in certain indications and an additional $25.0 million upon regulatory approval of maralixibat for each and every other indication. In addition, the Company is required to pay up to an aggregate of $30.0 million upon the achievement of certain clinical development and regulatory milestones for volixibat solely for the first indication sought. Upon commercialization, the Company is obligated to pay Shire product sales milestones on total licensed products up to an aggregate of $30.0 million. The Company is also obligated to pay tiered royalties with rates ranging from low double-digits to mid-teens based upon annual worldwide net sales for all licensed products; however, these royalties are reduced in part by royalties due under the Satiogen and Sanofi licenses, as discussed below, related to maralixibat and volixibat, as applicable. The Company’s royalty obligations will continue on a licensed product-by-licensed product and country-by-country basis until the later to occur of the expiration of the last valid claim in a licensed patent covering the applicable licensed product in such country, expiration of any regulatory exclusivity for the licensed product in a country and ten years after the first commercial sale of a licensed product in such country. The Company paid development milestones of $2.5 million in July 2019 related to the initiation of the Phase 3 MARCH clinical trial of maralixibat in PFIC and $10.0 million in December 2020 upon acceptance of an MAA filing to the EMA for maralixibat for the treatment of PFIC2. Development milestones achieved prior to regulatory approval of the product are expensed by the Company in the period incurred as research and development. In January 2019, the Company also entered into a Transition Services Agreement (“TSA”) with Shire, which covered services provided by Shire to transfer the research and development activities and the related know-how from Shire to the Company, including continuation of work on any existing clinical trials and manufacturing activities until fully transferred. All transition services were completed and all pass-through costs were settled as of June 30, 2019. As such, for the year ended December 31, 2020, there were no expenses for Shire provided services or pass-through costs recorded. The Company recorded $0.4 million for services provided by Shire under the TSA for the year ended December 31, 2019. Additionally, the Company recorded a reduction of estimated expenses of $0.1 million for pass-through costs related to continuation of work on existing clinical trials and manufacturing activities for the year ended December 31, 2019. The reduction of estimated expenses for the year ended December 31, 2019 was related to a final reconciliation of expenses and agreement on final amounts due to Shire. Satiogen License Through the Shire Agreement, the Company was assigned a license agreement with Satiogen pursuant to which the Company obtained an exclusive, worldwide license to certain patents and know-how, with the right to sublicense to a third party subject to certain financial considerations. The Company is obligated to pay to Satiogen up to an aggregate of $10.5 million upon the achievement of certain milestones, of which $0.5 million was for initiation of certain development activities, $5.0 million for the completion of regulatory approvals and $5.0 million for commercialization activities. Additionally, the Company will be required to pay a low single-digit royalty on net sales. The Company’s royalty obligations continue on a licensed product-by-licensed product and country-by-country basis until the expiration of the last valid claim in a licensed patent covering the applicable licensed product in such country. Royalty obligations under the Satiogen license are creditable against the royalty obligations to Shire under the Shire Agreement. In July 2019, the Company achieved a development milestone related to the initiation of the Phase 3 MARCH clinical trial of maralixibat in PFIC and made a $0.5 million payment to Satiogen, which was expensed by the Company as research and development expense. As of December 31, 2020, no additional milestones had been accrued as there were no other potential milestones yet considered probable. Pfizer License Through the Shire Agreement, the Company was assigned a license agreement with Pfizer pursuant to which the Company obtained an exclusive, worldwide license to certain Pfizer know-how with a right to sublicense. Upon commercialization of any product utilizing the licensed product, the Company will be required to pay to Pfizer a low single-digit royalty on net sales of product sold by the Company, its affiliates or sublicensees. The Company’s royalty obligations continue on a licensed product-by-licensed product basis until the eighth anniversary of the first commercial sale of such licensed product anywhere in the world. Sanofi License Through the Shire Agreement, the Company was assigned a license agreement with Sanofi pursuant to which the Company obtained an exclusive, worldwide license to certain patents and know-how with the right to sublicense to a third party subject to certain financial considerations. The Company is obligated to pay up to an aggregate of $36.0 million upon the achievement of certain regulatory, commercialization and product sales milestones. Additionally, upon commercialization, the Company is required to pay tiered royalties in the mid to high single-digit range based upon net sales of licensed products sold by the Company and sublicensees in a calendar year, subject to adjustments in certain circumstances. The Company’s royalty obligations continue on a licensed product-by-licensed product and country-by-country basis until the later to occur of the expiration of the last valid claim in a licensed patent covering the applicable licensed product in such country and ten years after the first commercial sale of a licensed product in such country. Royalty obligations under the Sanofi license are creditable against the royalty obligations to Shire under the Shire Agreement. As of December 31, 2020, no milestones had been accrued as there were no potential milestones yet considered probable.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	8. Leases In January 2019, the Company entered into an operating lease agreement for office space which consisted of approximately 5,600 square feet (the “initial lease”). The lease term is approximately four years with an option to extend the term for one five-year term, which at the time was not reasonably assured of exercise and therefore, not included in the lease term. The lease contained a tenant improvement allowance of $0.4 million, which has been recorded as leasehold improvements in the accompanying consolidated balance sheets with a corresponding reduction of the ROU asset at inception of the lease. In November 2019, the Company amended the operating lease agreement (the “amended agreement”) to extend the term of the initial lease through March 2025. This extension was accounted for as a lease modification and the Company recorded an increase to the ROU asset and lease liability of $0.6 million at the time of the amendment. Additionally, pursuant to the amended agreement, the Company expanded the office space by 5,555 square feet for a five-year term expiring in March 2025 (the “expanded space”). The Company accounted for the expanded space as a separate contract as there were material additional rights of use that were not included in the initial lease. The amended lease contained a tenant improvement allowance of $0.8 million in connection with the expanded space, which has been recorded as leasehold improvements on the accompanying consolidated balance sheet with a corresponding reduction of the ROU asset at inception of the lease for the expanded space. The ROU and corresponding lease liabilities were estimated using a weighted-average incremental borrowing rate of 8.0%. As of December 31, 2020, the Company recorded an aggregate ROU asset of $1.9 million and an aggregate lease liability of $3.3 million in the accompanying consolidated balance sheet. The weighted-average remaining lease term is 4.1 years. As of December 31, 2020, undiscounted future minimum payments under the Company’s operating leases are as follows (in thousands): Year Ended December 31, Undiscounted Rent Payments 2021 869 2022 893 2023 922 2024 930 2025 230 Thereafter — Total undiscounted lease payments 3,844 Less: imputed interest (581 ) Total lease liability $ 3,263 Rent expense was $0.6 million and $0.3 million for the years ended December 31, 2020 and 2019, respectively. Variable lease payments for lease operating expenses were immaterial for the years ended December 31, 2020 and 2019.

Stockholders_ Equity (Deficit)

Stockholders’ Equity (Deficit)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Stockholders’ Equity (Deficit)	9. Stockholders’ Equity (Deficit) Common Stock In July 2019, the Company completed its initial public offering (“IPO”) of its common stock. In connection with its IPO, the Company issued and sold 5,000,000 shares of its common stock at a price of $15.00 per share. As a result of the IPO, the Company received $67.2 million in net proceeds, after deducting underwriting discounts, commissions and offering expenses. At the closing of the IPO, 119,752,983 shares of outstanding Series A Preferred Stock were automatically converted into 14,969,118 shares of common stock , and 1,859,151 shares of redeemable common stock were reclassified into permanent equity due to the expiration of the deemed redemption feature In connection with the completion of its IPO, the Company amended and restated its certificate of incorporation to provide for 200,000,000 authorized shares of common stock with a par value of $0.0001 per share and 10,000,000 authorized shares of preferred stock with a par value of $0.0001 per share. Each share of common stock is entitled to one voting right. Common stockholders are entitled to dividends when funds are legally available and declared by the Company’s board of directors. In January 2020, the Company completed a follow-on public offering of its common stock, pursuant to which the Company sold 2,400,000 shares of common stock at a price of $20.00 per share, resulting in net proceeds of $44.7 million after deducting underwriting discounts, commissions and offering expenses. In August 2020, the SEC declared effective a registration statement on Form S-3 (“Shelf Registration”) covering the sale of up to $300.0 million of the Company’s securities. Also, in August 2020, the Company entered into a sales agreement (“Sales Agreement”) with SVB Leerink LLC (“SVB Leerink”) pursuant to which the Company may elect to issue and sell, from time to time, shares of common stock having an aggregate offering price of up to $75.0 million under the Shelf Registration through SVB Leerink acting as the sales agent and/or principal. During the year ended December 31, 2020, the Company sold 305,969 shares of common stock in an at-the-market offering pursuant to the Sales Agreement at a weighted-average price of $21.55 per share, resulting in gross proceeds of $6.6 million. The net proceeds after deducting sales commissions to SVB Leerink and other issuance expenses were approximately $6.3 million. The remaining capacity under the Sales Agreement is approximately $68.4 million as of December 31, 2020. In December 2020, the Company completed an underwritten public offering of its common stock pursuant to the Shelf Registration. The Company sold 3,750,000 shares of common stock at a price of $20.00 per share, resulting in net proceeds of $70.0 million after deducting underwriting discounts, commissions and offering expenses. In addition, the Company granted the underwriters an option, exercisable for 30 days, to purchase up to 562,500 additional shares of its common stock at the public offering price, less the underwriting discounts and commissions. In January 2021, the underwriters partially exercised their option and purchased 375,654 shares of the Company’s common stock at a price of $20.00 per share, resulting in net proceeds of $7.1 million after deducting underwriting discounts. As of December 31, 2020 and 2019, 256,056 and 389,649 shares of common stock, respectively, were subject to repurchase by the Company. The unvested stock liability related to these shares is immaterial to all periods presented. Common Stock Reserved for Issuance Common stock reserved for issuance is as follows: December 31, 2020 2019 Stock options issued and outstanding 5,071,740 3,366,812 Reserved for future stock awards or option grants 2,009,410 1,112,443 Reserved for employee stock purchase plan 700,023 500,000 Reserved for overallotment shares 562,500 — 8,343,673 4,979,255

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	10. Stock-Based Compensation Equity Incentive Plans In November 2018, the Company adopted the 2018 Equity Incentive Plan (the “2018 Plan”) which permits the granting of stock awards and incentive and nonstatutory stock options to employees, directors and consultants of the Company. In July 2019, the Company’s board of directors and stockholders approved and adopted the 2019 Equity Incentive Plan (the “2019 Plan”). The 2019 Plan became effective on July 17, 2019. Under the 2019 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other stock or cash-based awards to individuals who are then employees, officers, directors or consultants of the Company. A total of 1,401,443 shares of common stock were approved to be initially reserved for issuance under the 2019 Plan, including 101,443 shares that remained available for issuance under the 2018 Plan as of July 17, 2019. Shares subject to outstanding awards under the 2018 Plan as of the effective date of the 2019 Plan that are subsequently canceled, forfeited or repurchased by the Company will be added to the shares reserved under the 2019 Plan. In addition, the number of shares of common stock available for issuance under the 2019 Plan will be automatically increased on the first day of each calendar year during the ten-year term of the 2019 Plan, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to 5% of the outstanding number of shares of the Company’s common stock on December 31st of the preceding calendar year or such lesser amount as determined by the Company’s board of directors. As of December 31, 2020, 1,093,210 shares of common stock were available for issuance under the 2019 Plan. In March 2020, the compensation committee of the Company’s board of directors approved and adopted the 2020 Inducement Plan (the “2020 Inducement Plan”). Under the 2020 Inducement Plan, the Company may grant nonstatutory stock options, stock appreciation rights, restricted stock and restricted stock units to new employees entering into employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4). At adoption, the 2020 Inducement Plan authorized 750,000 shares of the Company’s common stock for future issuance. In December 2020, the Company’s board of directors authorized an additional 750,000 shares of the Company’s common stock for future issuance. As of December 31, 2020, 916,200 shares of common stock were available for issuance under the 2020 Inducement Plan. Stock Options The fair value of each employee and non-employee stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. Due to the Company’s limited operating history and a lack of company specific historical and implied volatility data, the Company estimated expected volatility based on the historical volatility of a group of similar companies that are publicly traded. The historical volatility data was computed using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. Due to the lack of historical exercise history, the expected term of the Company’s stock options for employees has been determined utilizing the “simplified” method for awards. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The following assumptions were used to estimate the fair value of stock option awards granted during the following period: Year ended December 31, 2020 2019 Exercise price $10.40-$26.59 $2.94-$15.00 Expected term (in years) 5.5-6.1 5.5-6.3 Expected volatility 77.07%-95.85% 73.88%-84.59% Risk-free interest rate 0.33%-1.73% 1.41%-2.46% Expected dividend yield — — Grant date fair value of options granted $7.38-$20.21 $5.10-$10.46 The following table summarizes stock option activity during the year ended December 31, 2020 (in thousands, except share and per share data): Number of Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in Years) Aggregate Intrinsic Value Outstanding as of December 31, 2019 3,366,812 $ 5.14 9.3 $ 65,235 Granted 2,070,267 $ 17.87 Exercised (47,604 ) $ 6.90 Canceled and forfeited (317,735 ) $ 10.45 Outstanding as of December 31, 2020 5,071,740 $ 9.99 8.6 $ 40,631 Vested and exercisable as of December 31, 2020 1,468,291 $ 5.12 8.1 $ 18,289 Intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of the common stock for the options that had exercise prices that were lower than the per share fair value of the common stock on the date of exercise. The weighted-average grant-date fair value per share of stock options granted during the years ended December 31, 2020 and 2019 was $12.70 and $8.29 per share, respectively. The total intrinsic value of options exercised during the years ended December 31, 2020 was $0.5 million. There were no options exercised during the year ended December 31, 2019. As of December 31, 2020, the total unrecognized stock-based compensation related to unvested stock option awards granted was $33.3 million, which the Company expects to recognize over a weighted-average period of approximately 2.7 years. In January 2021, the Company granted stock options to purchase an aggregate of 1,065,200 shares of common stock pursuant to the 2019 Plan at a weighted-average exercise price of $19.19 per share and stock options to purchase an aggregate of 126,400 shares of common stock pursuant to the 2020 Inducement Plan at a weighted-average exercise price of $19.89 per share. Restricted Stock In November 2018, in connection with the issuance of the Series A Preferred Stock, the Company’s founders agreed to modify their outstanding shares of common stock to include vesting provisions that require continued service to the Company in order to vest in those shares. As such, the 562,500 modified shares of common stock became compensatory upon such modification. The modified shares have a four-year vesting period and a measurement date fair value of $2.936 per share. For the years ended December 31, 2020 and 2019, 133,593 and 135,350 shares vested, respectively. The total fair value of shares vested during the years ended December 31, 2020 and 2019 was $0.4 million and $0.4 million, respectively, which was recorded as stock-based compensation in the consolidated statement of operations. As of December 31, 2020, the total unrecognized compensation expense related to unvested restricted stock was $0.8 million expected to be recognized over a weighted-average period of approximately 1.9 years. 2019 Employee Stock Purchase Plan In July 2019, the Company’s board of directors and stockholders approved and adopted the 2019 Employee Stock Purchase Plan (the “ESPP”). The ESPP became effective on July 17, 2019. A total of 500,000 shares of common stock were approved to be initially reserved for issuance under the ESPP. In addition, the number of shares of common stock available for issuance under the ESPP will be automatically increased on the first day of each calendar year during the first ten-years of the term of the ESPP, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to the lessor of (i) 1% of the outstanding number of shares of common stock on December 31st of the preceding calendar year, (ii) 1,500,000 shares of common stock or (iii) such lesser amount as determined by the Company’s board of directors. As of December 31, 2020, 29,876 shares were issued under the ESPP and the Company had 700,023 shares available for future issuance. Total stock-based compensation is reflected in the consolidated statements of operations as follows (in thousands): Year Ended December 31, 2020 2019 General and administrative $ 7,425 $ 3,711 Research and development 5,129 2,359 Total $ 12,554 $ 6,070

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes The Company’s losses before income taxes for the years ended December 31, 2020 and 2019 are as follows (in thousands): Year Ended December 31, 2020 2019 U.S. loss before taxes $ (103,371 ) $ (52,654 ) Foreign income before taxes 107 122 Loss before income taxes (103,264 ) (52,532 ) For the years ended December 31, 2020 and 2019, the Company had a current tax provision of $6,000 and $21,000 related to foreign taxes, respectively. A reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year Ended December 31, 2020 2019 Federal statutory income tax rate 21.00 % 21.00 % State tax 0.42 (1.62 ) Permanent differences (0.89 ) (0.78 ) Tax credits 6.42 7.32 Change in valuation allowance (26.96 ) (25.95 ) Total tax benefit (0.01 ) % (0.03 ) % Significant components of the Company’s deferred tax assets are as follows (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating losses $ 26,122 $ 9,486 Tax credit carryforwards 11,294 4,378 Accrued expenses 812 364 Intangibles 5,560 3,570 Lease liability 661 737 Stock-based compensation 2,769 989 Total deferred tax assets 47,218 19,524 Deferred tax liabilities: Operating lease right-of-use assets (385 ) (468 ) Fixed assets (184 ) (228 ) Total deferred tax liabilities (569 ) (696 ) Valuation allowance (46,649 ) (18,828 ) Net deferred tax assets $ — $ — The valuation allowance increased by $27.8 million and $13.6 million for the years ended December 31, 2020 and 2019, respectively. The tax benefit of deductible temporary differences or carryforwards is recorded as a deferred tax asset to the extent that management assesses the realization is “more likely than not.” Future realization of the tax benefit ultimately depends on the existence of sufficient taxable income within the period available under the tax law. At December 31, 2020 and 2019, the Company has set up valuation allowances against all federal and state net deferred tax assets because based on all available evidence, these deferred tax assets are not more than likely to be realizable. The Company had federal and state net operating loss carryforwards of approximately $123.5 million and $2.6 million at December 31, 2020, and $44.4 million and $2.2 million at December 31, 2019, respectively. Federal losses do not expire, and California net operating losses will begin to expire in 2038. The Company also has federal general business credit and California research and development credit carryforwards totaling $14.5 million and $0.9 million at December 31, 2020, and $5.6 million and $0.3 million at December 31, 2019, respectively. The federal research and development credit carryforwards will begin to expire in 2038, unless previously utilized. The California research credits do not expire. In general, if the Company experiences a greater than 50 percentage point aggregate change in ownership of certain significant stockholders over a three-year period (a “Section 382 ownership change”), utilization of its pre-change NOL carryforwards and the research and development credit carryforwards is subject to an annual limitation under Sections 382 and 383 of the Internal Revenue Code of 1986, as amended, and similar state laws. The annual limitation generally is determined by multiplying the value of the Company’s stock at the time of such ownership change, subject to certain adjustments, by the applicable long-term tax-exempt rate. Such limitations may result in expiration of a portion of the NOL carryforwards and research and development credit carryforwards before utilization and may be material. As of December 31, 2020, the Company has not determined to what extent a potential ownership change will impact the annual limitation that may be placed on the Company’s utilization of its NOL carryovers and research and development credit carryforwards. The Company recognizes the financial statements effects of a tax position when it is more likely than not, based on technical merits, that the position will be sustained upon examination. A reconciliation of the Company’s unrecognized tax benefits is as follows (in thousands): Year Ended December 31, 2020 2019 Balance at beginning of year $ 1,490 $ 116 (Decrease) related to prior year tax positions (17 ) (20 ) Increases related to current year tax positions 2,460 1,394 Balance at end of year $ 3,933 $ 1,490 The Company has considered the amounts and probabilities of the outcomes that can be realized upon ultimate settlement with the tax authorities and determined unrecognized tax benefits primarily related to credits should be established as noted in the summary rollforward above. The unrecognized tax benefits, if recognized and in absence of full valuation allowance, would impact the income tax provision by $3.6 million and $1.5 million in 2020 and 2019, respectively. The Company’s effective income tax rate would not be impacted if the unrecognized tax benefits are recognized in 2020 and 2019. As of December 31, 2020, the Company does not believe that it is reasonably possible that its unrecognized tax benefits would significantly change in the following 12 months. The Company is subject to taxation in the United States federal jurisdiction, state jurisdictions and Switzerland. Due to the Company’s losses incurred, the Company is subject to the income tax examination by authorities since inception on May 2, 2018. The Company’s policy is to recognize interest expense and penalties related to income tax matters as tax expense. As of December 31, 2020, there were no significant accruals for interest related to unrecognized tax benefits or tax penalties. The Company has not provided U.S. income or foreign withholding taxes on the undistributed earnings of its foreign subsidiaries as of December 31, 2020 and 2019, because it intends to permanently reinvest such earnings outside of the U.S. If these foreign earnings were to be repatriated in the future, the related U.S. tax liability will be immaterial, due to the participation exemption put in place in the Tax Act. We have elected to account for Global Intangible Low-taxed Income (GILTI) as a current period expense when incurred.

Contingencies

Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Contingencies	12. Contingencies The Company is subject to potential liabilities under government regulations and various claims and legal actions that are pending or may be asserted from time-to-time. These matters arise in the ordinary course and conduct of the Company’s business and may include, for example, commercial, intellectual property, and employment matters. The Company intends to defend itself vigorously in such matters and when warranted, take legal action against others. Furthermore, the Company regularly assesses contingencies to determine the degree of probability and range of possible loss for potential accrual in its financial statements. An estimated loss contingency is accrued in the Company’s financial statements if it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”).
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to the revenue interest liability, accrued research and development expenses, the valuation of derivative liabilities and the valuation allowance of deferred tax assets resulting from net operating losses. These estimates and assumptions are based upon historical experience, knowledge of current events and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results could differ materially from those estimates. In December 2019, a novel strain of coronavirus, which causes COVID-19, was identified. Due to the rapid and global spread of the virus, on March 11, 2020, the World Health Organization declared the COVID-19 outbreak a pandemic. To slow the proliferation of COVID-19, governments have implemented extraordinary measures, which include the mandatory closure of businesses, restrictions on travel and gatherings, and quarantine and physical distancing requirements. There were no significant estimates contained in the preparation of the Company’s consolidated financial statements or impacts to the Company’s consolidated financial statements for the year ended December 31, 2020 that were directly a result of the COVID-19 pandemic. The Company is not aware of any specific event or circumstance that would require an update to its estimates, judgments and assumptions or a revision of the carrying value of the Company’s assets or liabilities as of the date of this filing.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents. The carrying amounts reported in the consolidated balance sheets for cash and cash equivalents are valued at cost, which approximate their fair value. Cash equivalents may consist of money market accounts, money market funds, U.S. treasury bills and repurchase agreements.
Concentrations of Credit Risk and Off-Balance Sheet Risk	Concentrations of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents, and short and long-term investments. The Company minimizes the amount of credit exposure by investing cash that is not required for immediate operating needs in money market funds, government obligations and/or commercial paper with short maturities. To date, the Company has not experienced any losses associated with this credit risk and continues to believe that this exposure is not significant.
Investments	Investments The Company classifies all investments as available-for-sale, as the sale of such securities may be required prior to maturity . Management determines the appropriate classification of its investments in debt securities at the time of purchase. Investments with original maturities beyond three months at the date of purchase and which mature at, or less than twelve months from the balance sheet date, are classified as a current asset. Investments are recorded at fair value, with unrealized gains and losses reported as accumulated other comprehensive income (loss) until realized . 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. To date, the Company has not identified any other than temporary declines in fair value of its investments.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets; Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. The carrying amounts of all cash equivalents, accounts payable and accrued liabilities are reasonable estimates of their fair value.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost less accumulated depreciation. Depreciation is computed on a straight-line basis over the estimated useful lives of the related assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of their useful lives or the related lease term.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long -lived assets are reviewed for indications of possible impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amounts to the future undiscounted cash flows attributable to these assets. An impairment loss is recognized to the extent an asset group is not recoverable, and the carrying amount exceeds the projected discounted future cash flows arising from these assets. There were no impairments of long-lived assets for any of the periods presented.
Shelf Registration and Sales Agreement Deferred Offering Costs	Deferred Offering Costs Deferred offering costs directly related to the Company’s shelf registration and sales agreement primarily consisted of legal, accounting, printing and SEC filing fees. These costs are reclassified to additional paid-in capital on a pro-rata basis as the Company completes offerings under the shelf registration, with any remaining deferred costs to be charged to results of operations at the end of the three-year life of the shelf registration. During the year ended December 31, 2020, the deferred offering costs reclassified to additional paid-in capital as a result of the transactions contemplated under a shelf registration were $59,000.
Accrued Research and Development Expenses	Accrued Research and Development Expenses The Company accrues and expenses clinical trial activities performed by third parties based upon estimates of the proportion of work completed over the life of the individual study and patient enrollment rates in accordance with agreements established with clinical research organizations and clinical trial sites. The Company determines the estimates by reviewing contracts, vendor agreements and purchase orders and through discussions with internal clinical personnel and external service providers as to the progress or stage of completion of trials or services and the agreed-upon fee to be paid for such services. The Company makes estimates of accrued expenses as of each balance sheet date based on facts and circumstances known to the Company at that time. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. The Company has not experienced any material differences between accrued costs and actual costs incurred for the periods presented. Nonrefundable advance payments for goods and services are deferred and recognized as expense in the period that the related goods are consumed or services are performed.
Revenue Interest Liability, Net	Revenue Interest Liability, Net The revenue interest liability, net, associated with the Revenue Interest Purchase Agreement (“RIPA”) that the Company entered into in December 2020 A significant increase or decrease in net sales will materially impact the revenue interest liability, interest expense and the time period for repayment.
Derivative Liability	Derivative Liability The RIPA contains certain features that meet the definition of being embedded derivatives requiring bifurcation as a separate compound financial instrument apart from the RIPA. The derivative liability is initially measured at fair value on issuance and is subject to remeasurement at each reporting period with changes in fair value recognized as other income (expense) in the consolidated statements of operations as the change in fair value of derivative liability.
Research and Development Expenses	Research and Development Expenses Research and development expenses consist primarily of fees paid to contract research organizations and other vendors for clinical, non-clinical and manufacturing services, salaries and benefits, including stock-based compensation, consultant expenses, costs related to acquiring manufacturing materials, costs related to compliance with regulatory requirements and license payments related to acquiring intellectual property rights for the Company’s product candidates. Research and development expenses are expensed as incurred.
Leases	Leases The Company determines if a contractual arrangement is or contains a lease at inception. Operating lease right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset during the lease term, and operating lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating leases are included in ROU assets, current operating lease liabilities, and long-term operating lease liabilities on the accompanying consolidated balance sheets. Operating lease ROU assets and lease liabilities are initially recognized based on the present value of the future minimum lease payments over the lease term at commencement date calculated using the Company’s incremental borrowing rate applicable to the lease asset, unless the implicit rate is readily determinable. Operating lease ROU assets also include any lease payments made at or before lease commencement and exclude any lease incentives received. The Company determines the lease term as the noncancelable period of the lease and may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Leases with a term of 12 months or less are not recognized on the consolidated balance sheet. The Company’s leases do not contain any residual value guarantees. Lease expense for minimum lease payments is recognized as rent expense on a straight-line basis over the lease term.
Stock-Based Compensation	Stock-Based Compensation The Company recognizes stock-based compensation for all stock-based awards to employees based on the grant-date fair value of the award. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model, and the assumptions used in calculating the fair value of stock-based awards represent management’s estimates and involve inherent uncertainties and the application of management’s judgment. The fair value of equity awards that are expected to vest is amortized on a straight-line basis over the requisite service period. Stock-based compensation is recognized net of actual forfeitures when they occur.
Income Taxes	Income Taxes Income taxes are recorded using the liability method, under which deferred tax assets and liabilities are determined based on differences between financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Valuation allowances are recorded against deferred tax assets when it is determined it is more-likely-than-not that some or all of the tax benefits will not be realized. The Company accounts for uncertain tax positions in accordance with the provisions of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification No. 740, Income Taxes Interest and penalties related to unrecognized tax benefits, if any, are recorded as a component of income tax expense.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing net loss attributable to common stockholders by the weighted-average shares of common stock outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average shares of common stock and potentially dilutive securities outstanding for the period determined using the treasury-stock and if-converted methods. Diluted net loss per share excludes the potential impact of the Company’s common stock subject to repurchase, common stock options, contingently issuable employee stock purchase plan shares and contingently issuable overallotment shares because their effect would be anti-dilutive due to the Company’s net loss. Since the Company incurred a net loss in each of the periods presented, basic and diluted net loss per share were the same. The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: December 31, 2020 2019 Options to purchase common stock 5,071,740 3,366,812 Common stock subject to repurchase 256,056 389,649 Employee stock purchase plan contingently issuable 12,931 — Overallotment shares contingently issuable 562,500 — Total 5,903,227 3,756,461
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements On January 1, 2020, the Company adopted Accounting Standards Update (“ASU”) No. 2018-13, Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement (Topic 820) In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes (Topic 740) . The guidance eliminates certain exceptions for recognizing deferred taxes for investments, performing intraperiod allocation and calculating income taxes in interim periods. This guidance also includes guidance to reduce complexity in certain areas, including recognizing deferred taxes for tax goodwill and allocating taxes to members of a consolidated group. ASU 2019-12 is effective for annual and interim periods in fiscal years beginning after December 15, 2020. Early adoption is permitted. The Company early adopted this guidance in the fourth quarter of 2020. The adoption did not have a material impact on the Company’s consolidated financial statements. Other recent accounting pronouncements issued by the FASB (including its Emerging Issues Task Force), the American Institute of Certified Public Accountants, and the Securities and Exchange Commission (“SEC”) did not, or are not believed by management to, have a material impact on the Company’s consolidated financial position, results of operations or cash flows .
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instruments - Credit Losses Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Derivatives and Hedging (Topic 815), and Financial Instruments (Topic 842), Codification Improvements to Financial Instruments is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019 for public business entities, excluding smaller reporting companies. In August Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging-Contracts in Entity’s Own Equity (Subtopic 815-40) The Company is currently evaluating the impact this change will have on its consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Outstanding Potentially Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share	The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: December 31, 2020 2019 Options to purchase common stock 5,071,740 3,366,812 Common stock subject to repurchase 256,056 389,649 Employee stock purchase plan contingently issuable 12,931 — Overallotment shares contingently issuable 562,500 — Total 5,903,227 3,756,461

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities to Fair Value Measurements On Recurring Basis and Level of Input Measurements	Financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements by major security type are presented in the following table (in thousands): December 31, 2020 Level 1 Level 2 Level 3 Total Financial assets: Money market fund $ 127,783 $ — $ — $ 127,783 U.S. treasury bills 29,997 — — 29,997 Corporate debt securities — 23,201 — 23,201 Commercial paper — 41,460 — 41,460 U.S. government bonds — 5,066 — 5,066 Asset-backed securities — 2,006 — 2,006 Total financial assets $ 157,780 $ 71,733 $ — $ 229,513 Financial liabilities: Derivative liability — — 1,264 1,264 Total financial liabilities $ — $ — $ 1,264 $ 1,264 December 31, 2019 Level 1 Level 2 Level 3 Total Financial assets: Money market fund $ 10,621 $ — $ — $ 10,621 Corporate debt securities — 41,668 — 41,668 Commercial paper — 35,016 — 35,016 U.S. government bonds — 22,511 — 22,511 Asset-backed securities — 28,787 — 28,787 Total $ 10,621 $ 127,982 $ — $ 138,603
Summary of Change in Estimated Fair Value of Company's Derivative Liability Classified as Level 3	The following table provides a summary of the change in the estimated fair value of the Company’s derivative liability, classified as Level 3 in the fair value hierarchy: Balance at January 1, 2020 $ — Initial fair value of derivative liability 1,264 Balance at December 31, 2020 $ 1,264

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Fair Value and Amortized Cost of Cash Equivalents and Available-for-sale Investments by Major Security Type	The fair value and amortized cost of cash equivalents and available-for-sale investments by major security type are presented in the following table (in thousands): December 31, 2020 Amortized Cost Unrealized Gain Unrealized Loss Estimated Fair Value Cash equivalents and investments: Money market fund $ 127,783 — — $ 127,783 U.S. treasury bills 29,995 2 — 29,997 Corporate debt securities 23,126 75 — 23,201 Commercial paper 41,460 — — 41,460 U.S. government bonds 5,067 — (1 ) 5,066 Asset-backed securities 2,001 5 — 2,006 Total cash equivalents and investments $ 229,432 $ 82 $ (1 ) $ 229,513 Classified as: Cash equivalents $ 139,779 Short-term investments 89,734 Total cash equivalents and investments $ 229,513 December 31, 2019 Amortized Cost Unrealized Gain Unrealized Loss Estimated Fair Value Cash equivalents and investments: Money market fund $ 10,621 $ — $ — $ 10,621 Corporate debt securities 41,556 113 (1 ) 41,668 Commercial paper 35,016 — — 35,016 U.S. government bonds 22,492 19 — 22,511 Asset-backed securities 28,762 25 — 28,787 Total cash equivalents and investments $ 138,447 $ 157 $ (1 ) $ 138,603 Classified as: Cash equivalents $ 10,621 Short-term investments 104,690 Long-term investments 23,292 Total cash equivalents and investments $ 138,603

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): December 31, 2020 2019 Accrued clinical trials 3,673 4,795 Accrued professional service fees 2,157 777 Accrued contract manufacturing and non-clinical costs 2,780 1,540 Accrued compensation and related benefits 4,801 2,216 Total accrued expenses $ 13,411 $ 9,328

Revenue Interest Purchase Agr_2

Revenue Interest Purchase Agreement (Tables)	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Revenue Interest Liability	The following table summarizes the revenue interest liability activity during the year ended December 31, 2020 (in thousands): Revenue interest liability at inception $ 49,234 Interest expense recognized 335 Capitalized issuance costs (654 ) Debt discount from embedded derivatives (1,264 ) Revenue interest liability at December 31, 2020 $ 47,651

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Schedule of Undiscounted Future Minimum Payments under Operating Leases	As of December 31, 2020, undiscounted future minimum payments under the Company’s operating leases are as follows (in thousands): Year Ended December 31, Undiscounted Rent Payments 2021 869 2022 893 2023 922 2024 930 2025 230 Thereafter — Total undiscounted lease payments 3,844 Less: imputed interest (581 ) Total lease liability $ 3,263

Stockholders_ Equity (Deficit)

Stockholders’ Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Schedule of Common Stock Reserved for Issuance	Common stock reserved for issuance is as follows: December 31, 2020 2019 Stock options issued and outstanding 5,071,740 3,366,812 Reserved for future stock awards or option grants 2,009,410 1,112,443 Reserved for employee stock purchase plan 700,023 500,000 Reserved for overallotment shares 562,500 — 8,343,673 4,979,255

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Assumptions Used to Estimate Fair Value of Stock Option Awards Granted	The following assumptions were used to estimate the fair value of stock option awards granted during the following period: Year ended December 31, 2020 2019 Exercise price $10.40-$26.59 $2.94-$15.00 Expected term (in years) 5.5-6.1 5.5-6.3 Expected volatility 77.07%-95.85% 73.88%-84.59% Risk-free interest rate 0.33%-1.73% 1.41%-2.46% Expected dividend yield — — Grant date fair value of options granted $7.38-$20.21 $5.10-$10.46
Summary of Stock Option Activity	The following table summarizes stock option activity during the year ended December 31, 2020 (in thousands, except share and per share data): Number of Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in Years) Aggregate Intrinsic Value Outstanding as of December 31, 2019 3,366,812 $ 5.14 9.3 $ 65,235 Granted 2,070,267 $ 17.87 Exercised (47,604 ) $ 6.90 Canceled and forfeited (317,735 ) $ 10.45 Outstanding as of December 31, 2020 5,071,740 $ 9.99 8.6 $ 40,631 Vested and exercisable as of December 31, 2020 1,468,291 $ 5.12 8.1 $ 18,289
Summary of Stock-based Compensation Reflected in Consolidated Statements of Operations	Total stock-based compensation is reflected in the consolidated statements of operations as follows (in thousands): Year Ended December 31, 2020 2019 General and administrative $ 7,425 $ 3,711 Research and development 5,129 2,359 Total $ 12,554 $ 6,070

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Losses before Income Taxes	The Company’s losses before income taxes for the years ended December 31, 2020 and 2019 are as follows (in thousands): Year Ended December 31, 2020 2019 U.S. loss before taxes $ (103,371 ) $ (52,654 ) Foreign income before taxes 107 122 Loss before income taxes (103,264 ) (52,532 )
Summary of Reconciliation of Federal Statutory Income Tax Rate	A reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year Ended December 31, 2020 2019 Federal statutory income tax rate 21.00 % 21.00 % State tax 0.42 (1.62 ) Permanent differences (0.89 ) (0.78 ) Tax credits 6.42 7.32 Change in valuation allowance (26.96 ) (25.95 ) Total tax benefit (0.01 ) % (0.03 ) %
Significant Components of Deferred Tax Assets	Significant components of the Company’s deferred tax assets are as follows (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating losses $ 26,122 $ 9,486 Tax credit carryforwards 11,294 4,378 Accrued expenses 812 364 Intangibles 5,560 3,570 Lease liability 661 737 Stock-based compensation 2,769 989 Total deferred tax assets 47,218 19,524 Deferred tax liabilities: Operating lease right-of-use assets (385 ) (468 ) Fixed assets (184 ) (228 ) Total deferred tax liabilities (569 ) (696 ) Valuation allowance (46,649 ) (18,828 ) Net deferred tax assets $ — $ —
Reconciliation of Unrecognized Tax Benefits	A reconciliation of the Company’s unrecognized tax benefits is as follows (in thousands): Year Ended December 31, 2020 2019 Balance at beginning of year $ 1,490 $ 116 (Decrease) related to prior year tax positions (17 ) (20 ) Increases related to current year tax positions 2,460 1,394 Balance at end of year $ 3,933 $ 1,490

Organization and Description _2

Organization and Description of Business - Additional Information (Detail) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2019	Dec. 31, 2020USD ($)Segment	Dec. 31, 2019USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Date of incorporation		May 2, 2018
Number of operating segment | Segment		1
Reverse stock split ratio	0.125
Reverse stock split, description	In July 2019, the Company effected a 1-for-8 reverse stock split of its common stock. The par value and the authorized number of shares of common stock were not adjusted as a result of the reverse stock split. The reverse stock split resulted in an adjustment to the conversion price of the Company’s Series A redeemable convertible preferred stock (the “Series A Preferred Stock”) to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion.
Accumulated deficit		$ 173,171	$ 69,901
Cash, cash equivalents and investments		$ 231,800

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Summary Of Significant Accounting Policies [Line Items]
Investments with original maturities at date of purchase to be cash equivalents	3 months
Other than temporary declines in fair value of investments	$ 0	$ 0
Property and equipment, net	1,293,000	1,372,000
Accumulated depreciation	300,000	100,000
Impairment of long-lived assets	$ 0
Life of shelf registration	3 years
Deferred offering costs under shelf registration	$ 59,000,000
ASU No. 2018-13
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2020
Change in accounting principle, accounting standards update, adopted [true false]	true
Change in accounting principle, accounting standards update, immaterial effect [true false]	true
ASU No. 2019-12
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adoption date	Dec. 31, 2020
Change in accounting principle, accounting standards update, adopted [true false]	true
Change in accounting principle, accounting standards update, immaterial effect [true false]	true
Change in accounting principle, accounting standards update, early adoption [true false]	true
Leasehold Improvements
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, net	$ 1,300	1,300
Furniture and Fixtures
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, net	$ 300,000	$ 200,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, useful life	3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, useful life	5 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares of stock	5,903,227	3,756,461
Options to Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares of stock	5,071,740	3,366,812
Common Stock Subject to Repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares of stock	256,056	389,649
Employee Stock Purchase Plan Contingently Issuable
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares of stock	12,931	0
Overallotment Shares Contingently Issuable
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares of stock	562,500	0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities to Fair Value Measurement On Recurring Basis and Level of Input Measurement (Details) - Fair Value, Recurring Basis - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial assets:
Fair value measurements	$ 229,513	$ 138,603
Financial liabilities:
Derivative liability	1,264
Total financial liabilities	1,264
Level 1
Financial assets:
Fair value measurements	157,780	10,621
Level 2
Financial assets:
Fair value measurements	71,733	127,982
Level 3
Financial assets:
Fair value measurements		0
Financial liabilities:
Derivative liability	1,264
Total financial liabilities	1,264
Money Market Fund
Financial assets:
Fair value measurements	127,783	10,621
Money Market Fund | Level 1
Financial assets:
Fair value measurements	127,783	10,621
Money Market Fund | Level 2
Financial assets:
Fair value measurements		0
Money Market Fund | Level 3
Financial assets:
Fair value measurements		0
U.S. treasury bills
Financial assets:
Fair value measurements	29,997
U.S. treasury bills | Level 1
Financial assets:
Fair value measurements	29,997
Corporate Debt Securities
Financial assets:
Fair value measurements	23,201	41,668
Corporate Debt Securities | Level 1
Financial assets:
Fair value measurements		0
Corporate Debt Securities | Level 2
Financial assets:
Fair value measurements	23,201	41,668
Corporate Debt Securities | Level 3
Financial assets:
Fair value measurements		0
Commercial Paper
Financial assets:
Fair value measurements	41,460	35,016
Commercial Paper | Level 1
Financial assets:
Fair value measurements		0
Commercial Paper | Level 2
Financial assets:
Fair value measurements	41,460	35,016
Commercial Paper | Level 3
Financial assets:
Fair value measurements		0
U.S. Government Bonds
Financial assets:
Fair value measurements	5,066	22,511
U.S. Government Bonds | Level 1
Financial assets:
Fair value measurements		0
U.S. Government Bonds | Level 2
Financial assets:
Fair value measurements	5,066	22,511
U.S. Government Bonds | Level 3
Financial assets:
Fair value measurements		0
Asset Backed Securities
Financial assets:
Fair value measurements	2,006	28,787
Asset Backed Securities | Level 1
Financial assets:
Fair value measurements		0
Asset Backed Securities | Level 2
Financial assets:
Fair value measurements	$ 2,006	28,787
Asset Backed Securities | Level 3
Financial assets:
Fair value measurements		$ 0

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	Dec. 31, 2020
Discount Rate
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Discount rate used for valuation to derivative liability	0.159

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Change in Estimated Fair Value of Company's Derivative Liability Classified as Level 3 (Details) - Level 3 $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Initial fair value of derivative liability	$ 1,264
Balance at December 31, 2020	$ 1,264

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value and Amortized Cost of Cash Equivalents and Available-for-sale Investments by Major Security Type (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents and investments, Amortized cost	$ 229,432	$ 138,447
Cash equivalents and investments, Unrealized gain	82	157
Cash equivalents and investments, Unrealized loss	(1)	(1)
Cash equivalents and investments, Estimated Fair Value	229,513	138,603
Cash equivalents, Estimated Fair Value	139,779	10,621
Short-term investments	89,734	104,690
Long-term investments		23,292
Total cash equivalents and investments	229,513	138,603
Money Market Fund
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents, Amortized Cost	127,783	10,621
Cash equivalents, Estimated Fair Value	127,783	10,621
U.S. treasury bills
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments, Amortized Cost	29,995
Investments, Unrealized Gain	2
Investments, Estimated Fair Value	29,997
Corporate Debt Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments, Amortized Cost	23,126	41,556
Investments, Unrealized Gain	75	113
Investments, Unrealized Loss	0	(1)
Investments, Estimated Fair Value	23,201	41,668
Commercial Paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments, Amortized Cost	41,460	35,016
Investments, Unrealized Gain	0	0
Investments, Unrealized Loss	0	0
Investments, Estimated Fair Value	41,460	35,016
U.S. Government Bonds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments, Amortized Cost	5,067	22,492
Investments, Unrealized Gain	0	19
Investments, Unrealized Loss	(1)	0
Investments, Estimated Fair Value	5,066	22,511
Asset Backed Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments, Amortized Cost	2,001	28,762
Investments, Unrealized Gain	5	25
Investments, Estimated Fair Value	$ 2,006	$ 28,787

Financial Instruments - Additio

Financial Instruments - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Financial Instruments Owned At Fair Value [Abstract]
Realized gains or losses on available-for-sale investments	$ 0	$ 0
Investments in continuous unrealized loss position for more than 12 months	0	0
Other-than-temporary impairment losses	$ 0	$ 0

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued clinical trials	$ 3,673	$ 4,795
Accrued professional service fees	2,157	777
Accrued contract manufacturing and non-clinical costs	2,780	1,540
Accrued compensation and related benefits	4,801	2,216
Total accrued expenses	$ 13,411	$ 9,328

Revenue Interest Purchase Agr_3

Revenue Interest Purchase Agreement - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue interest liability	$ 47,651	$ 47,651	$ 0
Revenue Interest Purchase Agreement | Mulholland SA LLC,
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone payment to be received		150,000
Potential milestone payment to be received at the option of purchasers		$ 50,000
Percentage of revenue interest payments on annual net sales at Tier 1		9.75%
Percentage of revenue interest payments on annual net sales at Tier 2 and Tier 3		2.00%
Revenue interest rate percentage shall be reduced, if revenue interest payment percentage greater than or equal to 110% at Tier		2.00%
Revenue interest rate percentage shall be reduced, if revenue interest payment percentage greater than or equal to 110% at Tier 3		0.00%
Required revenue interest payment percentage of cumulative purchaser payments for termination		195.00%
Required repurchase price percentage of cumulative purchaser prior to first anniversary of closing date		120.00%
Required repurchase price percentage of cumulative purchaser payments after first anniversary and prior to third anniversary of closing date		175.00%
Required repurchase price percentage of cumulative purchaser after third anniversary of closing date		195.00%
Purchase agreement amount allocated to debt		$ 49,200
Initial fair value of derivative liability	1,300	1,300
Revenue interest liability	47,700	47,700
Debt issuance costs	700	700
Interest expense		$ 300
Revenue Interest Purchase Agreement | Mulholland SA LLC, | On or Prior to December 31, 2026
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Minimum required revenue interest payment percentage to cumulative purchaser payments to reduce interest rate		110.00%
Revenue Interest Purchase Agreement | Mulholland SA LLC, | Commercialization and Development of Product and Other Working Capital Needs
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue from purchase agreement	$ 50,000	$ 50,000
Revenue Interest Purchase Agreement | Mulholland SA LLC, | Maralixibat
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone payment received upon acceptance for review		65,000
Potential milestone payment received upon regulatory approval		35,000
Tier I | Mulholland SA LLC, | Maralixibat | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual net sales		350,000
Tier 2 | Mulholland SA LLC, | Maralixibat | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual net sales		350,000
Tier 2 | Mulholland SA LLC, | Maralixibat | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual net sales		1,100,000
Tier 3 | Mulholland SA LLC, | Maralixibat | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual net sales		$ 1,100,000
CSPA | Mulholland SA LLC,
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of shares sold		509,164
Aggregate purchase price		$ 10,000
Net proceeds from transaction		10,000
Purchase agreement amount allocated to common stock issued		$ 10,800

Revenue Interest Purchase Agr_4

Revenue Interest Purchase Agreement - Summary of Revenue Interest Liability (Details) $ in Thousands	1 Months Ended
	Dec. 31, 2020USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Revenue interest liability at inception	$ 49,234
Interest expense recognized	335
Capitalized issuance costs	(654)
Debt discount from embedded derivatives	(1,264)
Revenue interest liability at December 31, 2020	$ 47,651

Asset Acquisitions - Additional

Asset Acquisitions - Additional Information (Details)	1 Months Ended				12 Months Ended
	Jan. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Jul. 31, 2019USD ($)	Nov. 30, 2018USD ($)ProductCandidate$ / sharesshares	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Shire Agreement | Shire
Asset Acquisitions [Line Items]
Number of product candidates | ProductCandidate				2
Upfront Payment				$ 7,500,000
Product sales milestone payments, payable				30,000,000
Milestone payment			$ 2,500,000
Accrued milestones		$ 0			$ 0
Shire Agreement | Shire | Subsequent Event
Asset Acquisitions [Line Items]
Milestone payment	$ 2,000,000
Shire Agreement | Shire | Maralixibat
Asset Acquisitions [Line Items]
Milestone payments, payable				109,500,000
Milestone payments, payable upon approval				25,000,000
Milestone payment		10,000,000
Shire Agreement | Shire | Volixibat
Asset Acquisitions [Line Items]
Milestone payments, payable				$ 30,000,000
Shire Agreement | Shire | Redeemable Common Stock
Asset Acquisitions [Line Items]
Temporary equity, shares issued | shares				1,859,151
Issuance of Series A redeemable convertible preferred stock, net of issuance costs				$ 7,000,000
Shares issued, price per share | $ / shares				$ 3.76
Transition Services Agreement | Shire | Shire Provided Services
Asset Acquisitions [Line Items]
Research and development					0	$ 400,000
Transition Services Agreement | Shire | Pass-through Cost
Asset Acquisitions [Line Items]
Reduction of estimated expenses						100,000
Assigned License Agreement | Satiogen Pharmaceuticals, Inc.
Asset Acquisitions [Line Items]
Milestone payments, payable				$ 10,500,000
Milestone payments, payable upon approval				5,000,000
Accrued milestones						$ 0
Milestone payments, payable upon initiation				500,000
Milestone payments, payable upon commercialization				5,000,000
Assigned License Agreement | Sanofi-Aventis Deutschland GmbH
Asset Acquisitions [Line Items]
Milestone payments, payable				$ 36,000,000
Royalty obligations payment period				10 years
Milestones accrued		$ 0			$ 0
Assigned License Agreement | Maralixibat | Satiogen Pharmaceuticals, Inc.
Asset Acquisitions [Line Items]
Milestone payment			$ 500,000

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2019USD ($)ft²	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Jan. 31, 2019USD ($)	Jan. 22, 2019ft²
Lessee Lease Description [Line Items]
Area of office space | ft²					5,600
Term of lease					4 years
Operating lease, option to extend, description		The lease term is approximately four years with an option to extend the term for one five-year term, which at the time was not reasonably assured of exercise and therefore, not included in the lease term.
Existence of option to extend		true
Term of extension of lease				5 years
Tenant improvement allowance				$ 400
Operating lease right-of-use assets		$ 1,949	$ 2,361
Lease liability		$ 3,263
Weighted-average remaining lease term		4 years 1 month 6 days
Weighted-average incremental borrowing rate		8.00%
Rent expense		$ 600	$ 300
Amended Operating Lease Agreement
Lessee Lease Description [Line Items]
Term of lease	5 years
Tenant improvement allowance	$ 800
Additional area of office space | ft²	5,555
Lease expiration, month and year	2025-03
Amended Operating Lease Agreement | Restatement Adjustment
Lessee Lease Description [Line Items]
Operating lease right-of-use assets	$ 600
Lease liability	$ 600

Leases - Schedule of Undiscount

Leases - Schedule of Undiscounted Future Minimum Payments under Operating Leases (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Leases [Abstract]
2021	$ 869
2022	893
2023	922
2024	930
2025	230
Total undiscounted lease payments	3,844
Less: imputed interest	(581)
Total lease liability	$ 3,263

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) - Additional Information (Details)	1 Months Ended				12 Months Ended
	Jan. 31, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares	Jan. 31, 2020USD ($)$ / sharesshares	Jul. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2020USD ($)Vote$ / sharesshares	Dec. 31, 2019$ / sharesshares	Aug. 31, 2020USD ($)	Dec. 31, 2018shares
Class Of Stock [Line Items]
Preferred stock, par value | $ / shares		$ 0.0001		$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares authorized		10,000,000		10,000,000	10,000,000	10,000,000
Common stock, par value | $ / shares		$ 0.0001		$ 0.0001	$ 0.0001	$ 0.0001
Common stock, shares authorized		200,000,000		200,000,000	200,000,000	200,000,000
Maximum amount of sale covered in shelf registration statement | $							$ 300,000,000
Common stock aggregate offering price, remaining | $		$ 68,400,000			$ 68,400,000
SVB Leerink LLC
Class Of Stock [Line Items]
Maximum amount of offering issuance and sale covered in sales agreement | $							$ 75,000,000
Series A Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Redeemable stock, outstanding				119,752,983				59,908,284
Common Stock
Class Of Stock [Line Items]
Number of shares issued						5,000,000
Redeemable common stock reclassified to equity				1,859,151
Common stock, voting rights					Each share of common stock is entitled to one voting right.
Number of vote entitled for each common stockholder | Vote					1
Number of shares subject to repurchase		256,056			256,056	389,649
Common Stock | Sales Agreement
Class Of Stock [Line Items]
Proceeds from issuance of shares | $					$ 6,300,000
Gross proceeds from issuance of common stock | $					$ 6,600,000
IPO
Class Of Stock [Line Items]
Proceeds from issuance of shares | $				$ 67,200,000
IPO | Common Stock
Class Of Stock [Line Items]
Number of shares issued				5,000,000
Shares issued, price per share | $ / shares				$ 15
Number of redeemable convertible preferred stock converted into common stock				14,969,118
Follow-on Public Offering
Class Of Stock [Line Items]
Proceeds from issuance of shares | $			$ 44,700,000
Follow-on Public Offering | Common Stock
Class Of Stock [Line Items]
Number of shares issued			2,400,000
Shares issued, price per share | $ / shares			$ 20
At-the-market Offering | Common Stock
Class Of Stock [Line Items]
Number of shares issued					305,969
At-the-market Offering | Common Stock | Sales Agreement
Class Of Stock [Line Items]
Number of shares issued		3,750,000			305,969
Shares issued, price per share | $ / shares		$ 20			$ 20
Proceeds from issuance of shares | $		$ 70,000,000
At-the-market Offering | Common Stock | Sales Agreement | Weighted Average
Class Of Stock [Line Items]
Shares issued, price per share | $ / shares		$ 21.55			$ 21.55
Public Offering | Subsequent Event
Class Of Stock [Line Items]
Shares issued, price per share | $ / shares	$ 20
Proceeds from issuance of shares | $	$ 7,100,000
Public Offering | Common Stock | Subsequent Event
Class Of Stock [Line Items]
Number of shares purchased	375,654
Underwritten Public Offerings | Common Stock
Class Of Stock [Line Items]
Number of shares issued					6,150,000
Underwritten Public Offerings | Common Stock | Sales Agreement | Maximum
Class Of Stock [Line Items]
Number of shares issued		562,500

Stockholders' Equity (Deficit_2

Stockholders' Equity (Deficit) - Schedule of Common Stock Reserved for Issuance (Details) - shares	Dec. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Common stock reserved for issuance	8,343,673	4,979,255
Stock Options
Class Of Stock [Line Items]
Common stock reserved for issuance	5,071,740	3,366,812
Reserved for Future Stock Awards or Option Grants
Class Of Stock [Line Items]
Common stock reserved for issuance	2,009,410	1,112,443
Reserved for Employee Stock Purchase Plan
Class Of Stock [Line Items]
Common stock reserved for issuance	700,023	500,000
Overallotment Shares Contingently Issuable
Class Of Stock [Line Items]
Common stock reserved for issuance	562,500

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				12 Months Ended
	Jan. 31, 2021	Dec. 31, 2020	Jul. 31, 2019	Nov. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock approved and reserved for issuance		8,343,673			8,343,673	4,979,255
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock in connection with common stock option exercises, Shares					47,604
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock approved and reserved for issuance		5,071,740			5,071,740	3,366,812
Expected dividend yield					0.00%	0.00%
Grant date fair value of options granted					$ 12.70	$ 8.29
Stock-based compensation, Intrinsic value of options exercised					$ 0.5
Issuance of common stock in connection with common stock option exercises, Shares					47,604	0
Total unrecognized stock-based compensation related to unvested stock option awards granted		$ 33.3			$ 33.3
Unrecognized stock-based compensation related to unvested stock, expected to recognize over weighted-average period					2 years 8 months 12 days
Stock-based compensation, granted stock options to purchase					2,070,267
Stock-based compensation, weighted average exercise price					$ 17.87
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation related to unvested stock, expected to recognize over weighted-average period					1 year 10 months 24 days
Share vested					133,593	135,350
Total unrecognized compensation expense related to unvested restricted stock		$ 0.8			$ 0.8
Stock-based compensation, fair value of shares vested					$ 0.4	$ 0.4
Restricted Stock | Founder
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Measurement date fair value for stock issued for services				$ 2.936
Restricted Stock | Common Stock | Founder
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued for services				562,500
Vesting period				4 years
2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock approved and reserved for issuance		1,093,210	1,401,443		1,093,210
Equity incentive plans, description					A total of 1,401,443 shares of common stock were approved to be initially reserved for issuance under the 2019 Plan, including 101,443 shares that remained available for issuance under the 2018 Plan as of July 17, 2019. Shares subject to outstanding awards under the 2018 Plan as of the effective date of the 2019 Plan that are subsequently canceled, forfeited or repurchased by the Company will be added to the shares reserved under the 2019 Plan. In addition, the number of shares of common stock available for issuance under the 2019 Plan will be automatically increased on the first day of each calendar year during the ten-year term of the 2019 Plan, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to 5% of the outstanding number of shares of the Company’s common stock on December 31st of the preceding calendar year or such lesser amount as determined by the Company’s board of directors. As of December 31, 2020, 1,093,210 shares of common stock were available for issuance under the 2019 Plan.
Shares of common stock expiration term			10 years
Shares of common stock beginning date			Jan. 1, 2020
Shares of common stock ending date			Jan. 1, 2029
Percentage of annual increase in common stock available for issuance			5.00%
2019 Equity Incentive Plan | Stock Options | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation, granted stock options to purchase	1,065,200
Stock-based compensation, weighted average exercise price	$ 19.19
2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock approved and reserved for issuance			101,443
2020 Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock for future issuance							750,000
Common stock available for issuance					916,200
Number of additional common stock for future issuance		750,000
2020 Inducement Plan | Stock Options | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation, granted stock options to purchase	126,400
Stock-based compensation, weighted average exercise price	$ 19.89
2019 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock approved and reserved for issuance		700,023			700,023
Equity incentive plans, description					A total of 500,000 shares of common stock were approved to be initially reserved for issuance under the ESPP. In addition, the number of shares of common stock available for issuance under the ESPP will be automatically increased on the first day of each calendar year during the first ten-years of the term of the ESPP, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to the lessor of (i) 1% of the outstanding number of shares of common stock on December 31st of the preceding calendar year, (ii) 1,500,000 shares of common stock or (iii) such lesser amount as determined by the Company’s board of directors. As of December 31, 2020, 29,876 shares were issued under the ESPP and the Company had 700,023 shares available for future issuance.
Shares of common stock expiration term			10 years
Shares of common stock beginning date			Jan. 1, 2020
Shares of common stock ending date			Jan. 1, 2029
Percentage of annual increase in common stock available for issuance			1.00%
Stock issued for services			500,000		29,876
Annual increase in common stock available for issuance, shares			1,500,000

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Assumptions Used to Estimate Fair Value of Stock Option Awards Granted (Details) - Stock Options - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price, minimum	$ 10.40	$ 2.94
Exercise price, maximum	$ 26.59	$ 15
Expected volatility, minimum	77.07%	73.88%
Expected volatility, maximum	95.85%	84.59%
Risk-free interest rate, minimum	0.33%	1.41%
Risk-free interest rate, maximum	1.73%	2.46%
Expected dividend yield	0.00%	0.00%
Grant date fair value of options granted	$ 12.70	$ 8.29
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months
Grant date fair value of options granted	$ 7.38	$ 5.10
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 3 months 18 days
Grant date fair value of options granted	$ 20.21	$ 10.46

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Options, Outstanding
Number of shares, Outstanding, Beginning balance	3,366,812
Number of shares, Granted	2,070,267
Number of shares, Exercised	(47,604)	0
Number of shares, Canceled and forfeited	(317,735)
Number of shares, Outstanding, Ending balance	5,071,740	3,366,812
Number of shares, Vested and exercisable	1,468,291
Weighted-average exercise price, Outstanding
Weighted-average exercise price, Outstanding, Beginning balance	$ 5.14
Weighted-average exercise price, Granted	17.87
Weighted-average exercise price, Exercised	6.90
Weighted-average exercise price, Canceled and forfeited	10.45
Weighted-average exercise price, Outstanding, Ending balance	9.99	$ 5.14
Weighted-average exercise price, Vested and exercisable	$ 5.12
Share-based Payment Award, Options, Additional Disclosures
Weighted-average remaining contractual life, Outstanding	8 years 7 months 6 days	9 years 3 months 18 days
Weighted-average remaining contractual life, Vested and exercisable	8 years 1 month 6 days
Aggregate intrinsic value, Outstanding	$ 40,631	$ 65,235
Aggregate intrinsic value, Vested and exercisable	$ 18,289

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock-based Compensation Reflected in Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation	$ 12,554	$ 6,070
General and Administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation	7,425	3,711
Research and Development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation	$ 5,129	$ 2,359

Income Taxes - Schedule of Loss

Income Taxes - Schedule of Losses before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
U.S. loss before taxes	$ (103,371)	$ (52,654)
Foreign income before taxes	107	122
Net loss before provision for income taxes	$ (103,264)	$ (52,532)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax [Line Items]
Current tax provision related to foreign taxes	$ 6,000	$ 21,000
Valuation allowance, deferred tax asset, increase	27,800,000	13,600,000
Unrecognized tax benefits that would impact effective tax rate	3,600,000	1,500,000
Accruals for interest related to unrecognized tax benefits or tax penalties	0	0
Income or foreign withholding taxes on Undistributed earnings of foreign subsidiaries	0	0
Domestic Tax Authority
Income Tax [Line Items]
Operating loss carryforwards	123,500,000	44,400,000
Deferred tax assets, tax credit carryforwards, research and development	$ 14,500,000	5,600,000
Research and development credit carryforwards expiration, beginning year	2038
State and Local Jurisdiction | California Franchise Tax Board
Income Tax [Line Items]
Operating loss carryforwards	$ 2,600,000	2,200,000
Operating loss carryforwards expiration, beginning year	2038
Deferred tax assets, tax credit carryforwards, research and development	$ 900,000	$ 300,000

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Federal Statutory Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	21.00%
State tax	0.42%	(1.62%)
Permanent differences	(0.89%)	(0.78%)
Tax credits	6.42%	7.32%
Change in valuation allowance	(26.96%)	(25.95%)
Total tax benefit	(0.01%)	(0.03%)

Income Taxes - Significant Comp

Income Taxes - Significant Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating losses	$ 26,122	$ 9,486
Tax credit carryforwards	11,294	4,378
Accrued expenses	812	364
Intangibles	5,560	3,570
Lease liability	661	737
Stock-based compensation	2,769	989
Total deferred tax assets	47,218	19,524
Deferred tax liabilities:
Operating lease right-of-use assets	(385)	(468)
Fixed assets	(184)	(228)
Total deferred tax liabilities	(569)	(696)
Valuation allowance	(46,649)	(18,828)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 1,490	$ 116
(Decrease) related to prior year tax positions	(17)	(20)
Increases related to current year tax positions	2,460	1,394
Balance at end of year	$ 3,933	$ 1,490