0001564590-20-010498 | 10-K | XBRL Viewer

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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Mar. 10, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	KZR
Entity Registrant Name	Kezar Life Sciences, Inc.
Entity Central Index Key	0001645666
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		38,175,462
Entity Public Float			$ 119
Entity Interactive Data Current	Yes
Entity File Number	001-38542
Entity Tax Identification Number	47-3366145
Entity Address, Address Line One	4000 Shoreline Court
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	822-5600
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $0.001 par value
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the definitive proxy statement, or the Proxy Statement, for the 2020 Annual Meeting of Stockholders of the registrant are incorporated by reference into Part III of this Annual Report on Form 10-K. The Proxy Statement will be filed with the Securities and Exchange Commission within 120 days of the registrant’s fiscal year ended December 31, 2019.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 14,951	$ 24,182
Marketable securities	63,255	83,250
Prepaid expenses	1,878	1,884
Other current assets	1,048	489
Total current assets	81,132	109,805
Property and equipment, net	4,282	4,595
Operating lease right-of-use asset	3,817
Other assets	282	282
Total assets	89,513	114,682
Current liabilities:
Accounts payable	823	193
Accrued liabilities	4,218	2,678
Operating lease liabilities, current	900
Deferred rent, current		354
Other liabilities, current	62	112
Total current liabilities	6,003	3,337
Operating lease liabilities, noncurrent	5,464
Deferred rent, noncurrent		2,548
Total liabilities	11,467	5,885
Stockholders' equity:
Common stock, $0.001 par value, 125,000,000 shares authorized as of December 31, 2019 and 2018; 19,208,077 and 19,114,421 shares issued and outstanding as of December 31, 2019 and 2018, respectively	19	19
Preferred stock, $0.001 par value, 10,000,000 shares authorized, zero shares issued and outstanding as of December 31, 2019 and 2018
Additional paid-in capital	162,505	158,176
Accumulated other comprehensive loss	(196)	(203)
Accumulated deficit	(84,282)	(49,195)
Total stockholders' equity	78,046	108,797
Total liabilities and stockholders' equity	$ 89,513	$ 114,682

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	19,208,077	19,114,421
Common stock, shares outstanding	19,208,077	19,114,421
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses:
Research and development	$ 27,363	$ 18,136	$ 6,469
General and administrative	9,979	6,590	2,280
Total operating expenses	37,342	24,726	8,749
Loss from operations	(37,342)	(24,726)	(8,749)
Interest income	2,255	1,559	232
Net loss	$ (35,087)	$ (23,167)	$ (8,517)
Net loss per common share, basic and diluted	$ (1.84)	$ (2.26)	$ (14.21)
Weighted-average shares used to compute net loss per common share, basic and diluted	19,083,826	10,264,584	599,291

- Definition

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

+ References + Details

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (35,087)	$ (23,167)	$ (8,517)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(45)	(72)	39
Unrealized gain (loss) on marketable securities	52	(20)
Total other comprehensive income (loss), net of tax	7	(92)	39
Comprehensive loss	$ (35,080)	$ (23,259)	$ (8,478)

- Definition

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

+ References + Details

Consolidated Statement of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2016	$ (17,428)		$ 1	$ 232	$ (150)	$ (17,511)
Balance, shares at Dec. 31, 2016			948,578
Balance at Dec. 31, 2016		$ 28,176
Balance, shares at Dec. 31, 2016		5,966,753
Issuance of Series B redeemable convertible preferred stock for cash of $7.942 per share,net of $245 issuance costs		$ 49,755
Issuance of Series B redeemable convertible preferred stock for cash of $7.942 per share,net of $245 issuance costs, shares		6,296,373
Vesting related to shares of common stock issued pursuant to early exercises	16			16
Stock-based compensation expense	203			203
Other comprehensive income (loss)	39				39
Net loss	(8,517)					(8,517)
Balance at Dec. 31, 2017	(25,687)		$ 1	451	(111)	(26,028)
Balance, shares at Dec. 31, 2017			948,578
Balance at Dec. 31, 2017		$ 77,931
Balance, shares at Dec. 31, 2017		12,263,126
Conversion of redeemable convertible preferred stock to common stock	77,931		$ 12	77,919
Conversion of redeemable convertible preferred stock to common stock, shares			12,263,126
Conversion of redeemable convertible preferred stock to common stock		$ (77,931)
Conversion of redeemable convertible preferred stock to common stock, shares		(12,263,126)
Issuance of common stock upon initial public offering, net of issuance costs	77,695		$ 6	77,689
Issuance of common stock upon initial public offering, net of issuance costs, shares			5,750,000
Issuance of common stock under employee stock incentive plans, net of amount related to early exercised options	55			55
Issuance of common stock under employee stock incentive plans, net of amount related to early exercised options, shares			142,528
Issuance of Common Stock Upon Vesting of Restricted Stock Units			10,189
Vesting related to shares of common stock issued pursuant to early exercises	69			69
Stock-based compensation expense	1,993			1,993
Other comprehensive income (loss)	(92)				(92)
Net loss	(23,167)					(23,167)
Balance at Dec. 31, 2018	108,797		$ 19	158,176	(203)	(49,195)
Balance, shares at Dec. 31, 2018			19,114,421
Issuance of common stock under employee stock incentive plans, net of amount related to early exercised options	272			272
Issuance of common stock under employee stock incentive plans, net of amount related to early exercised options, shares			93,656
Vesting related to shares of common stock issued pursuant to early exercises	50			50
Stock-based compensation expense	4,007			4,007
Other comprehensive income (loss)	7				7
Net loss	(35,087)					(35,087)
Balance at Dec. 31, 2019	$ 78,046		$ 19	$ 162,505	$ (196)	$ (84,282)
Balance, shares at Dec. 31, 2019			19,208,077

Consolidated Statement of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - Series B Redeemable Convertible Preferred Stock $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares
Issuance of Series B redeemable convertible preferred stock, per share \| $ / shares	$ 7.942
Issuance of Series B redeemable convertible preferred stock, issuance costs \| $	$ 245

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (35,087)	$ (23,167)	$ (8,517)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,301	690	175
Stock-based compensation	4,007	1,993	203
Amortization of premiums and discounts on marketable securities	(979)	(476)
Loss on disposal of property and equipment		106
Changes in operating assets and liabilities
Prepaid expenses and other current assets	(553)	(1,136)	(543)
Other assets		61	(282)
Accounts payable and accrued liabilities	2,208	1,440	844
Operating lease liabilities and other liabilities	(774)	(8)	6
Deferred rent		(295)	5
Net cash used in operating activities	(29,877)	(20,792)	(8,109)
Cash flows from investing activities:
Purchases of property and equipment	(607)	(1,120)	(389)
Purchases of marketable securities	(102,255)	(119,244)
Maturities of marketable securities	123,281	36,450
Proceeds from sale of property and equipment		10
Net cash provided by (used in) investing activities	20,419	(83,904)	(389)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs		77,695
Proceeds from issuance of preferred stock, net of issuance costs			49,755
Proceeds from issuance of common stock under employee equity plans	272	218
Net cash provided by financing activities	272	77,913	49,755
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(45)	(81)	29
Net (decrease) increase in cash, cash equivalents and restricted cash	(9,231)	(26,864)	41,286
Cash, cash equivalents and restricted cash at the beginning of period	24,182	51,046	9,760
Cash, cash equivalents and restricted cash at the end of period	14,951	24,182	51,046
Supplemental disclosures of noncash investing and financing information:
Reclassification of employee stock liability to equity upon vesting	$ 50	69	16
Addition of tenant improvement paid by landlord		2,703	$ 464
Purchase of property and equipment in accounts payable		38
Conversion of redeemable convertible preferred stock into common stock		$ 77,931

Organization and Description of the Business

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Description of the Business

1. Organization and Description of the Business

Description of Business

Kezar Life Sciences, Inc. (the “Company”) was incorporated in Delaware on February 19, 2015, and commenced operations in June 2015. The Company is a clinical-stage biotechnology company, discovering and developing novel small molecule therapeutics to treat unmet needs in autoimmunity and cancer. The Company’s principal operations are in South San Francisco, California, and it operates in one segment.

Reverse Stock Split

On June 8, 2018, the Company filed an Amended and Restated Certificate of Incorporation effecting a 1-for-5.62 reverse stock split of its issued and outstanding shares of common stock and redeemable convertible preferred stock. The par value of the authorized stock was not adjusted as a result of the reverse stock split. In connection with the reverse stock split, the filed Amended and Restated Certificate of Incorporation also adjusted the minimum price per share required in a firm-commitment underwritten public offering of the Company’s common stock in order for the preferred stock to automatically convert to common stock. The minimum price post-split was $15.884 and was adjusted to $7.942. The Company did not adjust the number of authorized shares of common stock or redeemable convertible preferred stock. Other than the par value and the number of authorized shares of common stock and preferred stock, all share and per share data shown in the accompanying consolidated financial statements and related notes have been retroactively revised to reflect the reverse stock split.

Initial Public Offering

On June 25, 2018, the Company completed its initial public offering (“IPO”), whereby the Company issued 5,750,000 shares of its common stock (inclusive of 750,000 shares of common stock pursuant to the full exercise of an overallotment option granted to the underwriters in connection with the offering) at a price of $15.00 per share. The shares began trading on The Nasdaq Global Select Market on June 21, 2018. The net proceeds received by the Company from the offering were approximately $77.7 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company of approximately $8.6 million. Upon the closing of the IPO, all outstanding shares of redeemable convertible preferred stock converted into 12,263,126 shares of common stock. Additionally, the Company is now authorized to issue 125,000,000 shares of common stock and 10,000,000 shares of preferred stock.

Liquidity

Since commencing operations in mid-2015, substantially all of the Company’s efforts have been focused on research, development, and the advancement of the Company’s lead product candidate, KZR-616. The Company’s ultimate success depends on the outcome of the ongoing research and development activities. The Company has not yet generated product sales and as a result has experienced operating losses since inception and had an accumulated deficit of $84.3 million as of December 31, 2019. The Company expects to incur additional losses in the future to conduct research and development and will need to raise additional capital to fully implement management’s business plan. The Company intends to raise such capital through the issuance of additional equity, and potentially through borrowings, strategic alliances with partner companies and other licensing transactions. However, if such financing is not available at adequate levels, the Company may need to reevaluate its operating plans. Management believes that its cash, cash equivalents and marketable securities as of December 31, 2019, and the $53.3 million in net proceeds received from the February Offering, will be sufficient to fund the Company’s cash requirements for at least 12 months following the issuance of these financial statements.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation and Consolidation

The consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the Company’s accounts and those of its wholly owned Australian subsidiary, Kezar Life Sciences Australia Pty Ltd, which is a proprietary company limited by shares. All intercompany balances and transactions have been eliminated upon consolidation.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Significant items subject to such estimates and assumptions include the valuation of marketable securities, useful lives of fixed assets, stock-based compensation, and accrued research and development costs. Management bases its estimates on historical experience and on various other market-specific relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates.

Foreign Currency Translation

The functional currency of the Company’s non-U.S. subsidiary is the Australian dollar. Asset and liability balances denominated in non-U.S. dollar currency are translated into U.S. dollars using period-end exchange rates, while expenses are based upon the exchange rate at the time of the transaction, if known, or at the average rate for the period. Equity accounts, except for the change in accumulated deficit during the year, have been translated using historical exchange rates. Differences are included in stockholders’ equity as a component of accumulated other comprehensive loss.

Cash, Cash Equivalents and Restricted Cash

The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents are stated at fair value.

Restricted cash consisted of deposits at the bank held as collateral for the Company’s credit card program. The collateral requirement was removed and released in May 2018.

The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total of the same amounts shown in the consolidated statements of cash flows (in thousands):

	Year Ended December 31,
	2019		2018		2017
Cash and cash equivalents	$	14,951	$	24,182	$	51,033
Restricted cash		—		—		13
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$	14,951	$	24,182	$	51,046

Marketable Securities

All marketable securities have been classified as “available-for-sale” and are carried at fair value, based upon quoted market prices. The Company considers its available-for-sale portfolio as available for use in current operations. Unrealized gains and losses, net of any related tax effects, are excluded form earnings and are included in other comprehensive income or loss and reported as a separate component of stockholders’ equity or deficit until realized. Realized gains and losses and declines in value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense), net. The cost of securities sold is based on the specific-

identification method. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion, together with interest on securities, are included in interest income on the Company’s consolidated statements of operations. In accordance with the Company’s investment policy, management invests to diversify credit risk and only invests in debt securities with high credit quality, including U.S. government securities.

The Company regularly reviews all of its investments for other-than-temporary declines in estimated fair value. Its review includes the consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. When the Company determines that the decline in estimated fair value of an investment is below the amortized cost basis and the decline is other-than-temporary, it reduces the carrying value of the security and record a loss for the amount of such decline. The Company has not recorded any realized losses or declines in value judged to be other than temporary on its investments in debt securities.

Concentration of Credit Risk

Financial instruments that potentially expose the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. As of December 31, 2019, the majority of the Company’s cash, cash equivalents and marketable securities were held by financial institutions in the United States, while approximately $0.2 million was held by a financial institution in Australia. Such deposits in the United States may be in excess of insured limits.

Impairment of Long-Lived Assets

Long-lived assets include property and equipment. The Company reviews the carrying value of long-lived assets for impairment whenever events or changes in circumstances indicate that the assets may not be recoverable. The Company recognizes an impairment loss when the total estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount. Through December 31, 2019, there have been no such impairment losses.

Property and Equipment

Property and equipment are stated at cost, less accumulated depreciation. Depreciation on property and equipment is calculated on the straight-line method over the estimated useful lives of the assets. Furniture, laboratory and office equipment are depreciated over five to seven years. Computer equipment are depreciated over three years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term.

Other Assets

Other assets consist of security deposits for the Company’s operating leases of office and laboratory space.

Leases

At lease commencement, the Company records a lease liability based on the present value of lease payments over the expected lease term. The Company calculates the present value of lease payments using the discount rate implicit in the lease, unless that rate cannot be readily determined. In that case, the Company uses its incremental borrowing rate, which is the rate of interest that the Company would have to pay to borrow on a collateralized basis an amount equal to the lease payments over the expected lease term. The Company records a corresponding right-of-use (“ROU”) lease asset based on the lease liability, adjusted for any lease incentives received and any initial direct costs paid to the lessor prior to the lease commencement date.

After lease commencement, the Company measures its leases as follows: (i) the lease liability based on the present value of the remaining lease payments using the discount rate determined at lease commencement; and (ii) the ROU lease asset based on the remeasured lease liability, adjusted for any unamortized lease incentives received, any

unamortized initial direct costs and the cumulative difference between rent expense and amounts paid under the lease agreement. Any lease incentives received and any initial direct costs are amortized on a straight-line basis over the expected lease term. Rent expense is recorded on a straight-line basis over the expected lease term.

The Company elected the short-term lease recognition exemption for all leases that qualify. This means, for those leases that qualify, the Company will not recognize ROU assets or lease liabilities, and this includes not recognizing ROU assets or lease liabilities for existing short-term leases of those assets in transition. The Company did not elect to apply the practical expedient to not separate lease and non-lease components for all of its leases.

Research and Development Costs

Research and development costs are expensed as incurred and consist primarily of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to nonemployees and entities that conduct certain research and development activities on the Company’s behalf and expenses incurred in connection with license agreements. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and then expensed as the related goods are delivered or the services are performed.

The Company accrues for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of preclinical and clinical studies and contract manufacturing activities. The Company estimates the amount of work completed through discussions with internal personnel and external service providers as to the progress or stage of completion of the services and the agreed-upon fee to be paid for such services. The Company makes significant judgments and estimates in determining the accrued balance in each reporting period. As actual costs become known, the Company adjusts the accrued estimates. Although the Company does not expect the estimates to be materially different from amounts actually incurred, the status and timing of services performed, the number of patients enrolled and the rate of patient enrollment may vary from the Company’s estimates and could result in the Company reporting amounts that are too high or too low in any particular period. The Company’s accrued expenses are dependent, in part, upon the receipt of timely and accurate reporting from clinical research organizations and other third-party service providers. To date, there have been no material differences from the Company’s accrued expenses to actual expenses.

Research and Development Tax Incentive

The Company is eligible under the AusIndustry Research and Tax Development Tax Incentive Program to obtain a cash amount from the Australian Taxation Office (ATO). The tax incentive is available to the Company on the basis of specific criteria with which the Company must comply related to research and development expenditures in Australia. These research and development tax incentives are recognized as contra research and development expense when the right to receive has been attained and funds are considered to be collectible.

The Company recognized $635,000, $5,000 and $499,000 as a reduction of research and development expenses for the years ended December 31, 2019, 2018 and 2017, respectively, in connection with the research and development tax incentive from the ATO. As of December 31, 2019 and 2018, the research and development tax credit receivable was $642,000 and $5,000, respectively, which is included in other current assets in the consolidated balance sheets.

Stock-Based Compensation

Stock-based awards issued to employees, directors and nonemployee consultants, including stock options, are recorded at fair value as of the grant date using the Black-Scholes option pricing model and recognized as expense on a straight line-basis over the employee’s or director’s requisite service period (generally the vesting period). The Company accounts for forfeitures as they occur by reversing any expense recognized for unvested awards.

Income Taxes

Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are

measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date.

The Company records a valuation allowance against deferred tax assets if it is more likely than not that a portion or all of the asset will not be realized in future periods. In making such determination, the Company considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax planning strategies and recent financial operations.

The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest charges or penalties related to unrecognized tax benefits.

Net Loss per Share

Basic net loss per share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is the same as basic net loss per share for the periods presented since the effects of potentially dilutive securities are antidilutive given the net loss of the Company.

Accounting Pronouncements Adopted in 2019

Leases (Topic 842)

In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842), or ASU 2016-02. ASU 2016-02 increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and requires disclosing key information about leasing arrangements. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements, which provides entities the option to initially apply the transition provisions of ASU 2016-02 at its adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption.

The Company adopted the new standard on January 1, 2019 and used the effective date as its date of initial application. Consequently, financial information will not be restated and the disclosures required under the new standard will not be provided for dates and periods before January 1, 2019. The Company elected the package of transition practical expedients that allows the Company not to reassess the lease classification for any expired or existing contracts, whether initial direct costs were incurred, or whether any expired or existing contracts contained leases.

This standard had a material effect on the Company’s consolidated financial statements. The most significant effects relate to: (1) the recognition of new ROU asset and lease liabilities on the balance sheet for the operating lease for the Company’s headquarters at 4000 Shoreline Court, Suite 300, South San Francisco, California; and (2) providing significant new disclosures about its leasing activities.

The following table discloses the impact on the Company’s balance sheet upon adoption (in thousands):

	January 1, 2019		December 31, 2018
Operating lease ROU asset	$	4,236	$	—
Operating lease liabilities, current		774		—
Operating lease liabilities, noncurrent		6,364		—
Deferred rent, current		—		354
Deferred rent, noncurrent		—		2,548

Stock Compensation (Topic 718)

In June 2018, the FASB issued ASU No. 2018-07, Compensation – Stock Compensation (Topic 718), which simplifies the accounting for nonemployee share-based payment transactions. This ASU is effective for public entities for interim and annual reporting periods beginning after December 15, 2018. The Company adopted the new standard on January 1, 2019 and determined that it did not have a material impact on the Company’s consolidated financial statements.

New Accounting Pronouncements Not Yet Adopted

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326), which requires measurement and recognition of expected credit losses for financial assets. This guidance will become effective for us beginning in the first quarter of 2020 and must be adopted using a modified retrospective approach, with certain exceptions. Early adoption is permitted beginning in the first quarter of 2019. The Company does not expect the adoption of this guidance to have a material impact on its consolidated financial statements.

In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement, or ASU 2018-13, which modifies the disclosure requirements on fair value measurements. The amendment of ASU No. 2018-13 removes disclosure requirements from Topic 820 in the areas of (1) the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; (2) the policy for timing of transfers between levels, and (3) the valuation processes for Level 3 fair value measurements. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. The Company does not expect the adoption of this guidance to have a material impact on its consolidated financial statements.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes: Simplifying the Accounting for Income Taxes. The new guidance is intended to simplify aspects of the accounting for income taxes, including the elimination of certain exceptions to the guidance in ASC740, Income Taxes related to the approach for intraperiod tax allocation, among other changes. This guidance will be effective for annual periods beginning after December 15, 2020 and interim periods within, with early adoption permitted. The Company is currently evaluating the effect the new guidance will have on its consolidated financial statements.

Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash, cash equivalents, marketable securities, other current assets, accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows:

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

Level 2: Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

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

Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the

fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability.

The Company applies fair value accounting for all financial assets and liabilities and nonfinancial assets and liabilities that are required to be recognized or disclosed at fair value in the financial statements. The Company determines the fair value of Level 1 assets using quoted prices in active markets for identical assets. The Company reviews trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented.

In certain cases, where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3 within the valuation hierarchy. The Company did not have any assets or liabilities measured using Level 3 inputs as of December 31, 2019 or 2018.

The following table summarizes our financial assets measured at fair value on a recurring basis and classified under the appropriate level of the fair value hierarchy as described above (in thousands):

	December 31, 2019
	Total		Level 1		Level 2		Level 3
Financial Assets:
Money market funds	$	14,731	$	14,731			$	—
U.S. Treasury securities		5,285		5,285				—
Commercial paper		15,186				15,186		—
Corporate debt securities		17,171				17,171		—
U.S. agency bonds		25,613				25,613		—
Total	$	77,986	$	20,016	$	57,970	$	—

	December 31, 2018
	Total		Level 1		Level 2		Level 3
Financial Assets:
Money market funds	$	23,156	$	23,156	$	—	$	—
U.S. Treasury securities		25,692		25,692		—		—
Commercial paper		19,190		—		19,190		—
Corporate debt securities		20,451		—		20,451		—
U.S. agency bonds		17,917		—		17,917		—
Total	$	106,406	$	48,848	$	57,558	$	-

- Definition

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

+ References + Details

Available-for-Sale Securities

12 Months Ended

Dec. 31, 2019

Investments Debt And Equity Securities [Abstract]

Available-for-Sale Securities

4. Available-for-Sale Securities

The following table is a summary of available-for-sale securities recorded in cash and cash equivalents or marketable securities in our consolidated balance sheets as of December 31, 2019 and 2018 (in thousands):

	December 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Financial Assets:
Money market funds	$	14,731	$	—	$	—		$	14,731
U.S. Treasury securities		5,285		1		(1	)		5,285
Commercial paper		15,174		12		—			15,186
Corporate debt securities		17,168		3		—			17,171
U.S. agency bonds		25,597		16		—			25,613
Total	$	77,955	$	32	$	(1	)	$	77,986

	December 31, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Financial Assets:
Money market funds	$	23,156	$	—	$	—		$	23,156
U.S. Treasury securities		25,698		—		(6	)		25,692
Commercial paper		19,203		—		(13	)		19,190
Corporate debt securities		20,449		4		(2	)		20,451
U.S. agency bonds		17,921		—		(4	)		17,917
Total	$	106,427	$	4	$	(25	)	$	106,406

The Company believes that the individual unrealized losses represent temporary declines primarily resulting from interest rate changes, and intends to hold these marketable securities to their maturities.

As of December 31, 2019, the amortized cost and estimated fair value of the Company’s available-for-sale securities by contractual maturity are shown below (in thousands):

	Amortized		Estimated
	Cost		Fair Value
Available-for-sale securities maturing:
In one year or less	$	77,955	$	77,986
Total available-for-sale securities	$	77,955	$	77,986

The Company currently does not intend to sell these securities prior to maturity and does not consider these investments to be other-than-temporarily impaired at December 31, 2019. There were no sales of available-for-sale securities in any of the periods presented.

Balance Sheet Components

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Balance Sheet Components

5. Balance Sheet Components

Property and Equipment, Net

Property and equipment consists of the following (in thousands):

	December 31, 2019			December 31, 2018
Leasehold improvements	$	3,268		$	3,268
Furniture, laboratory and office equipment		2,578			2,043
Computer equipment		253			219
Total property and equipment		6,099			5,530
Less accumulated depreciation and amortization		(1,817	)		(935	)
Property and equipment, net	$	4,282		$	4,595

Depreciation expense was $0.9 million for the year ended December 31, 2019, $0.7 million for the year ended December 31, 2018 and $0.2 million for the year ended December 31, 2017.

Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	December 31, 2019		December 31, 2018
Accrued preclinical and research costs	$	1,687	$	1,146
Accrued clinical costs		1,027		434
Accrued employee-related costs		1,293		736
Accrued professional services		53		138
Other		158		224
Total accrued liabilities	$	4,218	$	2,678

Lease

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Lease

6. Lease

In August 2017, the Company entered into a lease agreement to lease 24,357 square feet of combination laboratory and office space in 4000 Shoreline Court, South San Francisco, California. The lease commenced on March 1, 2018 and terminates on February 28, 2025.

The contractually specified minimum rent and annual rent increases for the operating lease are included in the measurement of the ROU asset and related lease liabilities. Under the lease arrangement, we may be required to pay directly, or reimburse the lessor for real estate taxes, insurance, utilities, maintenance and other operating costs. Such amounts are generally variable and therefore not included in the measurement of the ROU asset and related lease liability but are instead recognized as variable lease expense in our Condensed Consolidated Statements of Operations when they are incurred. The operating lease agreement has one option to extend the lease term for a period of five years at the fair market rate at the time of the extension. The option to extend the lease was not recognized as part of the Company’s lease liability and ROU asset as the Company determined the renewal rent costs are uncertain and the option is not reasonably certain to be exercised.

Because the rate implicit in the lease is not readily determinable, the Company uses its incremental borrowing rate to determine the present value of the lease payments. The Company recorded lease liabilities and ROU asset for its office lease based on the present value of lease payments over the expected lease term. As of December 31, 2019, the weighted average remaining lease term was 5.17 years and the weighted average discount rate used to determine the operating lease liability was 10.0%.

Information related to the Company’s ROU asset and related lease liabilities were as follows (in thousands):

	Twelve months Ended December 31, 2019

Cash paid for operating lease liabilities	$	774
Operating lease costs		1,099
Variable lease costs		505
ROU asset obtained in exchange for operating lease obligation		4,236

Maturities of lease liabilities as of December 31, 2019 were as follows for the years ending December 31:
2020	$	1,497
2021		1,542
2022		1,588
2023		1,635
2024		1,684
Thereafter		282
Total undiscounted lease payments		8,228
Less: imputed interest		(1,864	)
Total lease liabilities	$	6,364

Operating lease liabilities, current		900
Operating lease liabilities, noncurrent		5,464
Total operating lease liabilities	$	6,364

ASC 840 Disclosure

The Company elected the alternative modified transition method and included the following table previously disclosed. As of December 31, 2018, future minimum lease payments under the noncancelable facility operating lease, were as follows (in thousands):

Year ending December 31:
2019	$	1,453
2020		1,497
2021		1,542
2022		1,588
2023		1,635
2024		1,684
Thereafter		282
Total future minimum lease payments	$	9,681

For the years ended December 31, 2019, 2018 and 2017, the Company recognized $1.1 million, $1.0 million and $0.3 million of rent expense, respectively. Variable lease costs were $0.5 million, $0.4 million and $0.1 million for the years ended December 31, 2019, 2018 and 2017, respectively.

Redeemable Convertible Preferred Stock

12 Months Ended

Dec. 31, 2019

Temporary Equity Disclosure [Abstract]

Redeemable Convertible Preferred Stock

7. Redeemable Convertible Preferred Stock

In connection with the completion of the Company’s IPO in June 2018, all outstanding shares of convertible preferred stock converted into 12,263,126 shares of common stock.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

8. Stock-Based Compensation

Stock Incentive Plans

2018 Equity Incentive Plan

In June 2018, the Company’s board of directors adopted and its stockholders approved the 2018 Equity Incentive Plan (the “2018 Plan”), which became effective as of June 20, 2018, at which point no further grants could be made under the 2015 Equity Incentive Plan (the “2015 Plan”) described below. Under the 2018 Plan, the Company may grant incentive stock options (“ISOs”), nonstatutory stock options (“NSOs”), stock appreciation rights, restricted stock awards, restricted stock units (“RSUs”) and other stock-based awards. As of December 31, 2019, options to purchase 1,271,992 shares of common stock were outstanding under the 2018 Plan and 1,765,266 shares were available for future issuance under the 2018 Plan.

Initially, subject to adjustment as provided in the 2018 Plan, the aggregate number of shares of the Company’s common stock authorized for issuance pursuant to stock awards under the 2018 Plan was 4,000,000 shares, which is the sum of (i) 1,600,692 shares plus (ii) the number of shares reserved and available for issuance under the 2015 Plan at the time the 2018 Plan became effective and (iii) the number of shares subject to stock options or other stock awards granted under the 2015 Plan that expire, terminate, are forfeited or otherwise not issued, or are withheld to satisfy a tax withholding obligation in connection with an award or to satisfy a purchase or exercise price of an award (such as upon the expiration or termination of a stock award prior to vesting). The number of shares of the Company’s common stock reserved for issuance under the 2018 Plan automatically increases on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2028, by 5% of the total number of shares of capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors prior to such increase. The maximum number of shares that may be issued upon the exercise of ISOs under the 2018 Plan is 12,500,000 shares.

2015 Equity Incentive Plan

The Company’s 2015 Plan provided for the granting of ISOs and NSOs to employees, directors and consultants at the discretion of the board of directors. The 2015 Plan was terminated as to future awards in June 2018, although it continues to govern the terms of options that remain outstanding under the 2015 Plan.

No additional stock awards will be granted under the 2015 Plan, and all outstanding stock awards granted under the 2015 Plan that are repurchased, forfeited, expire or are cancelled will become available for grant under the 2018 Plan in accordance with its terms.

Options granted under the 2015 Plan expire no later than 10 years from the date of grant. Options granted under the 2015 Plan vest over periods determined by the board of directors, generally over four years. The 2015 Plan allows for early exercise of certain options prior to vesting. Upon termination of employment, the unvested shares are subject to repurchase at the original exercise price. As of December 31, 2019, options to purchase 1,835,074 shares of common stock were outstanding under the 2015 Plan.

2018 Employee Stock Purchase Plan

In June 2018, the Company’s board of directors adopted and its stockholders approved the 2018 Employee Stock Purchase Plan (the “ESPP”), which became effective as of June 20, 2018. The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the U.S. Internal Revenue Code of 1986, as amended (the “Code”). The number of shares of common stock initially reserved for issuance under the ESPP was 200,000 shares. The ESPP provides for an annual increase on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2028, equal to the lesser of (i) 1% of the shares of common stock outstanding on the last day of the prior fiscal year or (ii) 375,000 shares, or a lesser number of shares determined by the Company’s board of directors prior to such increase. As of December 31, 2019, 26,656 shares of common stock had been issued under the ESPP and 364,488 shares remained available for future issuance under the ESPP. The price per share of common stock to be paid by an ESPP participant on the applicable purchase date of an offering period shall be equal to 85% of the lesser of the fair market value of a share of common stock on (i) the applicable offering date or (ii) the applicable purchase date. The Company’s board of directors authorized an initial six-month offering period beginning on November 16, 2018 and ending on May 15, 2019. Additional six-month offering periods began on May 16, 2019 and on November 16, 2019.

Stock Option Activity

The following table summarizes activity under the Company’s stock option plans and related information (in thousands, except share and per share amounts):

	Number of Options Outstanding			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding at December 31, 2018		2,181,466		$	3.80		8.5	$	43,189
Options granted		1,248,871		$	13.36
Options exercised		(67,000	)	$	0.90			$	292
Options cancelled		(256,271	)	$	10.04
Outstanding at December 31, 2019		3,107,066		$	7.19		8.2	$	3,151
Vested and exercisable at December 31, 2019		1,478,773		$	4.59		7.4	$	2,322

The weighted average grant date fair value of options granted during the years ended December 31, 2019 and 2018 was $9.33 and $4.23 per share, respectively. The aggregate intrinsic value of exercised stock options during the years ended December 31, 2019 and 2018 was $292,000 and $370,000, respectively. The aggregate intrinsic value is calculated as the difference between the exercise price and the estimated fair value of the Company’s common stock at the date of exercise.

Early Exercise Stock Options

The 2015 Plan allows for early exercisable option grants, which permit the holder to exercise a stock option for the purchase of common stock before the requisite service is provided (i.e., before the award is vested under its original terms); however, such arrangements permit the Company to subsequently repurchase at the exercise price any shares of common stock for which the applicable vesting conditions have not been satisfied. Under the 2015 Plan, the Company only made such early exercisable option grants to non-employee members of our board of directors.

As of December 31, 2019 and 2018, there were 30,027 and 68,349 shares, respectively, of nonvested common stock outstanding that were exercised early and remain subject to repurchase by the Company at the original issuance price upon termination of the stockholder’s services. The right to repurchase these shares generally lapses with respect to 25% of the shares underlying the option one year after the applicable vesting commencement date and 1/48 of the shares underlying the option each month for 36 months thereafter. The shares purchased pursuant to the early exercise of stock options are not deemed, for accounting purposes, to be issued until those shares vest. The cash received in exchange for exercised and nonvested shares related to stock options granted is recorded as a liability for the early exercise of stock options on the balance sheets with the corresponding par value in common stock and an offset in additional paid-in capital. As of December 31, 2019 and 2018, the Company recorded in other current liabilities $62,000 and $112,000, respectively, associated with shares issued upon the early exercise of stock options that are subject to repurchase.

Restricted Stock Units Granted to Employees

During the year ended December 31, 2018, the Company granted RSUs to certain employees to receive 10,189 shares of common stock pursuant to the 2018 Plan with a weighted-average estimated grant-date fair value of $17.75 per share. These RSUs were fully vested on the grant date. The valuation of these RSUs totaled $181,000 and was recognized as stock-based compensation expense in June 2018. There were no RSUs granted during the year ended December 31, 2019.

Stock Options Granted to Employees That Contain Performance Condition

During year ended December 31, 2018, the Company granted options to two of its executive officers to purchase an aggregate 115,657 shares of common stock that vested fully upon the closing of the Company’s IPO on June 25, 2018. The aggregate fair value of these options was estimated at $474,000 and was recognized as stock-based

compensation expense in June 2018. There were no such options granted that contained performance condition during the year ended December 31, 2019.

Restricted Stock

In addition to the nonvested shares of common stock outstanding described above under the section titled “Early Exercise Stock Options,” the Company issued restricted stock to its founders. The fair value of restricted stock on the issuance date is deemed equal to the cash consideration paid by the founders. Restricted stock vests over a four-year period from the applicable vesting commencement date. The following summarizes the vesting activity of restricted stock:

	Number of Shares
Nonvested—December 31, 2018		20,908
Vested		(20,908	)
Nonvested—December 31, 2019		-

Stock-Based Compensation Expense

Total stock-based compensation expense recognized by function was as follows (in thousands):

	Year Ended December 31,
	2019		2018		2017
Research and development	$	1,777	$	842	$	93
General and administrative		2,230		1,151		110
Total stock-based compensation expense	$	4,007	$	1,993	$	203

As of December 31, 2019, the unrecognized stock-based compensation cost was $10.3 million with an estimated weighted average amortization period of 2.5 years.

The fair value of the employee stock options granted and the ESPP rights to purchase common stock of the Company is calculated using the Black-Scholes option-pricing model with the following weighted-average assumptions:

	Options							ESPP Rights
	Year Ended December 31,							Year Ended December 31,
	2019		2018		2017			2019		2018			2017
Expected term (years)	5.8 - 5.9		5.5 - 6.1			6.1			0.5		0.5			—
Expected volatility	78.7 - 83.7%		82.0 - 83.2%			89.8	%	73.7 - 109.9%			74.3	%		—
Risk-free interest rate	1.5 - 2.6%		2.6 - 3.1%			2.0	%	1.6 - 2.4%			2.5	%		—
Expected dividend yield		—		—		—			—		—			—

The expected term of options granted represents the period of time that options granted are expected to be outstanding and was determined by calculating the midpoint between the date of vesting and the contractual life of each option. The expected term of the ESPP rights is equal to the six-month look-back period. Volatility is based on the average historical volatility of a peer group of public companies over the expected term. The peer group was selected on the basis of operational and economic similarity with the Company’s principal business operations. The risk-free interest rate for the expected term of the options is based on the U.S. Treasury yield curve with a maturity equal to the expected term in effect at the time of grant. The Company has not paid, and does not anticipate paying, cash dividends on its shares of common stock; therefore, the expected dividend yield is zero.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

9. Commitments & Contingencies

Indemnification

In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third-party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. The Company has also entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by California corporate law. The Company currently has directors’ and officers’ insurance.

License Agreement

12 Months Ended

Dec. 31, 2019

License Agreement [Abstract]

License Agreement

10. License Agreement

In June 2015, the Company entered into an exclusive license agreement with Onyx Therapeutics, Inc. (“Onyx”), a wholly owned subsidiary of Amgen, Inc., for a worldwide, exclusive license under certain patents, and a non-exclusive license to certain know-how, in each case controlled by Onyx and relating to the Company’s immunoproteasome program. The Company may be required to make future payments of up to $172.5 million upon achievement of certain development and commercial milestones for KZR-616, as well as royalty payments in the mid to high single digits on future annual net sales, if any.

Defined Contribution Plan

12 Months Ended

Dec. 31, 2019

Compensation And Retirement Disclosure [Abstract]

Defined Contribution Plan

11. Defined Contribution Plan

The Company has a qualified 401(k) Savings and Investment Plan (the “Plan”) whereby employees may contribute up to the lesser of $56,000 or 100% of their pre-tax compensation. The total contributed amount from the employees is only up to Federal annual limits. The Company matches $1.00 for every $1.00 contributed to the Plan by participants up to the first 4% of base compensation and incentive cash bonus (subject to statutory limits). During the years ended December 31, 2019, 2018 and 2017, the Company recorded matching contributions of approximately $249,000, $167,000 and $77,000, respectively.

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

12. Income Taxes

No provision for income taxes was recorded for the years ended December 31, 2019, 2018 and 2017. The U.S. federal deferred tax assets generated from the Company’s net operating losses have been fully reserved, as the Company believes it is not more likely than not that the benefit will be realized.

The following table presents domestic and foreign components of net loss for the periods presented (in thousands):

	Year Ended December 31,
	2019			2018			2017
Domestic	$	(34,181	)	$	(23,047	)	$	(7,551	)
Foreign		(906	)		(120	)		(966	)
Total	$	(35,087	)	$	(23,167	)	$	(8,517	)

In December 2015, the Protecting Americans from Tax Hikes Act of 2015 (“PATH”) was signed into law, which created several new research and development (“R&D”) tax credit provisions, including allowing qualified small businesses to utilize the R&D credit against the employer’s portion of payroll tax up to a maximum of $250,000 per year. The Company qualified as a small business under PATH for 2016, 2017 and 2018. The Company has utilized $284,000 and $175,000 of R&D tax credits as a reduction of payroll expenses to offset its payroll tax liabilities for the years ended December 31, 2019 and 2018, respectively.

The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows:

	Year Ended December 31,
	2019				2018				2017
Federal statutory income tax rate		21.0		%		21.0		%		34.0		%
State taxes, net of federal benefit		0.9				6.4				6.0
Foreign tax rate differential		0.2				0.1				(0.5	)
Permanent differences		(1.7	)			0.3				(3.8	)
Research and development credit		1.9				1.4				2.5
Federal rate change impact		0.0				0.0				(31.4	)
Change in valuation allowance		(22.3	)			(29.2	)			(6.8	)
Provision for income taxes		—		%		—		%		—		%

The components of the deferred tax assets and liabilities are as follows (in thousands):

	Year Ended December 31,
	2019			2018			2017
Deferred tax assets
Reserves and accruals	$	1,056		$	1,009		$	169
Net operating loss carryforwards		16,986			10,985			6,802
Research and development credit carryforwards		2,177			1,194			515
Lease Liabilities		1,336			—			—
Gross deferred tax assets		21,555			13,188			7,486
Valuation allowance		(20,196	)		(12,560	)		(7,434	)
Net deferred tax assets		1,359			628			52
Deferred tax liabilities
Property and equipment		(557	)		(628	)		(52	)
Right-of-use asset		(802	)		—			—
Net deferred tax	$	—		$	—		$	—

Realization of the deferred tax assets is dependent upon future taxable income. Since the amount and timing of future income are uncertain, the net deferred tax assets, as of December 31, 2019, and December 31, 2018 have been fully offset by a valuation allowance. The valuation allowance increased approximately $7.6 million, $5.1 million and $0.4 million during the years ended December 31, 2019, 2018, and 2017, respectively.

As of December 31, 2019, the Company had federal net operating loss (“NOL”) carryforward of $72.7 million and a federal research and development tax credit carryforward of $1.3 million. If not utilized sooner, the federal NOL generated through December 31, 2017 and tax credit carryforwards will expire, beginning in 2035. Federal net operating loss carryforwards of $50.6 million generated from years ended after December 31, 2017, carryforward indefinitely. As of December 31, 2019 the Company had a state NOL carryforward of $17.3 million, which will expire beginning in 2035, and a state research and development tax credit carryforward of $1.1 million, which does not expire.

As of December 31, 2019, the Company also had accumulated Australian tax losses of $1.9 million available for carry forward against future earnings, which under relevant tax laws do not expire but may not be available under certain circumstances.

In general, if the Company experiences a greater than 50 percentage point aggregate change in ownership over a three-year period (a Section 382 ownership change), utilization of the Company’s pre-change NOL carryforwards is subject to an annual limitation under Section 382 of the Code and similar California 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 before utilization. The Company has not utilized any NOL

carryforwards through December 31, 2019. In addition, the Company’s deferred tax assets are subject to a full valuation allowance, and thus no benefit for deferred tax assets is recorded on the Company’s books. The Company’s ability to use the remaining NOL carryforwards may be further limited if the Company experiences a Section 382 ownership change as a result of future changes in the Company’s stock ownership.

No liability related to uncertain tax positions is recorded on the financial statements. All uncertain tax positions are currently recorded as a reduction to our deferred tax assets. Since inception, there have been no interest charges or penalties related to unrecognized tax benefits.

The Company files income tax returns in the United States federal jurisdiction, state jurisdictions and Australia. The Company currently has no federal, state or other jurisdictional tax examinations in progress. The Company did not recognize any accrued interest and penalties related to gross unrecognized tax benefits related to the year ended December 31, 2019. All years are open for examination by federal, state and Australian authorities.

Net Loss per Share

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Net Loss Per Share

13. Net Loss Per Share

Net Loss Per Share

The following table sets forth the calculation of basic and diluted net loss per share during the periods presented (in thousands, except share and per share data):

	Year Ended December 31,
	2019			2018			2017
Numerator:
Net loss	$	(35,087	)	$	(23,167	)	$	(8,517	)
Denominator:
Weighted-average shares of common stock outstanding		19,083,826			10,264,584			599,291
Net loss per share, basic and diluted	$	(1.84	)	$	(2.26	)	$	(14.21	)

The following outstanding shares of common stock equivalents were excluded from the computation of the diluted net loss per share for the periods presented because their effect would have been anti-dilutive:

	Year Ended December 31,
	2019		2018		2017
Redeemable convertible preferred stock on an if converted basis		—		—		12,263,126
Options to purchase common stock		3,107,066		2,181,466		1,213,010
Common stock subject to future vesting		30,027		89,257		238,618
Total		3,137,093		2,270,723		13,714,754

Selected Quarterly Financial Information (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Information (Unaudited)

14. Selected Quarterly Financial Information (Unaudited)

The following amounts are in thousands, except per share amounts:

	Quarter Ended
(in thousands, except per share amounts)	March 31, 2019			June 30, 2019			September 30, 2019			December 31, 2019
	(Unaudited)
Operating expenses	$	8,309		$	9,355		$	9,681		$	9,997
Net loss	$	(7,642	)	$	(8,718	)	$	(9,148	)	$	(9,579	)
Net loss per share, basic and diluted	$	(0.40	)	$	(0.46	)	$	(0.48	)	$	(0.50	)

	Quarter Ended
(in thousands, except per share amounts)	March 31, 2018			June 30, 2018			September 30, 2018			December 31, 2018
	(Unaudited)
Operating expenses	$	5,086		$	6,950		$	6,264		$	6,426
Net loss	$	(4,947	)	$	(6,775	)	$	(5,663	)	$	(5,782	)
Net loss per share, basic and diluted	$	(6.53	)	$	(3.31	)	$	(0.30	)	$	(0.30	)

Basic and diluted net loss per share is computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share amounts may not equal annual basic and diluted net loss per share amounts.

Subsequent Events

12 Months Ended

Dec. 31, 2019

Subsequent Events [Abstract]

Subsequent Events

15. Subsequent Events

On February 4, 2020, the Company completed an underwritten public offering of 18,965,385 shares of its common stock, which includes the full exercise of the underwriters’ option to purchase additional shares of common stock, and pre-funded warrants to purchase 2,884,615 shares of its common stock. The public offering price of the common stock was $2.60 per share and the public offering price of each pre-funded warrant was $2.599 per underlying share. The net proceeds from the public offering were approximately $53.3 million, after deducting underwriting discounts and commissions and other offering expenses paid by the Company. The Company’s existing stockholder, Morningside Ventures, together with its affiliate, and certain of the Company’s officers and directors purchased an aggregate amount of approximately $22.9 million of common stock in the offering.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Basis of presentation and consolidation

Basis of Presentation and Consolidation

Use of Estimates

Foreign Currency Translation

Cash, Cash Equivalents and Restricted Cash

The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents are stated at fair value.

Restricted cash consisted of deposits at the bank held as collateral for the Company’s credit card program. The collateral requirement was removed and released in May 2018.

	Year Ended December 31,
	2019		2018		2017
Cash and cash equivalents	$	14,951	$	24,182	$	51,033
Restricted cash		—		—		13
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$	14,951	$	24,182	$	51,046

Marketable Securities

Concentration of Credit Risk

Impairment of Long-Lived Assets

Property and Equipment

Other Assets

Other assets consist of security deposits for the Company’s operating leases of office and laboratory space.

Leases

Research and Development Costs

Research and Development Tax Incentive

Stock-Based Compensation

Income Taxes

Net Loss per Share

Accounting Pronouncements Adopted in 2019 and New Accounting Pronouncements Not Yet Adopted

Accounting Pronouncements Adopted in 2019

Leases (Topic 842)

The following table discloses the impact on the Company’s balance sheet upon adoption (in thousands):

	January 1, 2019		December 31, 2018
Operating lease ROU asset	$	4,236	$	—
Operating lease liabilities, current		774		—
Operating lease liabilities, noncurrent		6,364		—
Deferred rent, current		—		354
Deferred rent, noncurrent		—		2,548

Stock Compensation (Topic 718)

New Accounting Pronouncements Not Yet Adopted

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash

	Year Ended December 31,
	2019		2018		2017
Cash and cash equivalents	$	14,951	$	24,182	$	51,033
Restricted cash		—		—		13
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$	14,951	$	24,182	$	51,046

Impact of Accounting Pronouncements Adoption on Balance Sheet

The following table discloses the impact on the Company’s balance sheet upon adoption (in thousands):

	January 1, 2019		December 31, 2018
Operating lease ROU asset	$	4,236	$	—
Operating lease liabilities, current		774		—
Operating lease liabilities, noncurrent		6,364		—
Deferred rent, current		—		354
Deferred rent, noncurrent		—		2,548

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured at Fair Value on a Recurring Basis

	December 31, 2019
	Total		Level 1		Level 2		Level 3
Financial Assets:
Money market funds	$	14,731	$	14,731			$	—
U.S. Treasury securities		5,285		5,285				—
Commercial paper		15,186				15,186		—
Corporate debt securities		17,171				17,171		—
U.S. agency bonds		25,613				25,613		—
Total	$	77,986	$	20,016	$	57,970	$	—

	December 31, 2018
	Total		Level 1		Level 2		Level 3
Financial Assets:
Money market funds	$	23,156	$	23,156	$	—	$	—
U.S. Treasury securities		25,692		25,692		—		—
Commercial paper		19,190		—		19,190		—
Corporate debt securities		20,451		—		20,451		—
U.S. agency bonds		17,917		—		17,917		—
Total	$	106,406	$	48,848	$	57,558	$	-

Available-for-Sale Securities (Tables)

12 Months Ended

Dec. 31, 2019

Investments Debt And Equity Securities [Abstract]

Summary of Available-For-Sale Securities Recorded in Cash and Cash Equivalents or Marketable Securities

	December 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Financial Assets:
Money market funds	$	14,731	$	—	$	—		$	14,731
U.S. Treasury securities		5,285		1		(1	)		5,285
Commercial paper		15,174		12		—			15,186
Corporate debt securities		17,168		3		—			17,171
U.S. agency bonds		25,597		16		—			25,613
Total	$	77,955	$	32	$	(1	)	$	77,986

	December 31, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Financial Assets:
Money market funds	$	23,156	$	—	$	—		$	23,156
U.S. Treasury securities		25,698		—		(6	)		25,692
Commercial paper		19,203		—		(13	)		19,190
Corporate debt securities		20,449		4		(2	)		20,451
U.S. agency bonds		17,921		—		(4	)		17,917
Total	$	106,427	$	4	$	(25	)	$	106,406

Summary of Amortized Cost and Estimated Fair Value of Available-for-sale Securities by Contractual Maturity

As of December 31, 2019, the amortized cost and estimated fair value of the Company’s available-for-sale securities by contractual maturity are shown below (in thousands):

	Amortized		Estimated
	Cost		Fair Value
Available-for-sale securities maturing:
In one year or less	$	77,955	$	77,986
Total available-for-sale securities	$	77,955	$	77,986

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Property and Equipment

Property and equipment consists of the following (in thousands):

	December 31, 2019			December 31, 2018
Leasehold improvements	$	3,268		$	3,268
Furniture, laboratory and office equipment		2,578			2,043
Computer equipment		253			219
Total property and equipment		6,099			5,530
Less accumulated depreciation and amortization		(1,817	)		(935	)
Property and equipment, net	$	4,282		$	4,595

Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	December 31, 2019		December 31, 2018
Accrued preclinical and research costs	$	1,687	$	1,146
Accrued clinical costs		1,027		434
Accrued employee-related costs		1,293		736
Accrued professional services		53		138
Other		158		224
Total accrued liabilities	$	4,218	$	2,678

Lease (Tables)

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Details of Right-of-Use Assets and Lease Liabilities

Information related to the Company’s ROU asset and related lease liabilities were as follows (in thousands):

	Twelve months Ended December 31, 2019

Cash paid for operating lease liabilities	$	774
Operating lease costs		1,099
Variable lease costs		505
ROU asset obtained in exchange for operating lease obligation		4,236

Maturities of lease liabilities as of December 31, 2019 were as follows for the years ending December 31:
2020	$	1,497
2021		1,542
2022		1,588
2023		1,635
2024		1,684
Thereafter		282
Total undiscounted lease payments		8,228
Less: imputed interest		(1,864	)
Total lease liabilities	$	6,364

Operating lease liabilities, current		900
Operating lease liabilities, noncurrent		5,464
Total operating lease liabilities	$	6,364

Schedule of Future Minimum Lease Payments Under Noncancelable Facility Operating Lease

ASC 840 Disclosure

Year ending December 31:
2019	$	1,453
2020		1,497
2021		1,542
2022		1,588
2023		1,635
2024		1,684
Thereafter		282
Total future minimum lease payments	$	9,681

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Activity under Stock Option Plans and Related Information

The following table summarizes activity under the Company’s stock option plans and related information (in thousands, except share and per share amounts):

	Number of Options Outstanding			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding at December 31, 2018		2,181,466		$	3.80		8.5	$	43,189
Options granted		1,248,871		$	13.36
Options exercised		(67,000	)	$	0.90			$	292
Options cancelled		(256,271	)	$	10.04
Outstanding at December 31, 2019		3,107,066		$	7.19		8.2	$	3,151
Vested and exercisable at December 31, 2019		1,478,773		$	4.59		7.4	$	2,322

Summarizes of Activity of Nonvested Restricted Stock

The following summarizes the vesting activity of restricted stock:

	Number of Shares
Nonvested—December 31, 2018		20,908
Vested		(20,908	)
Nonvested—December 31, 2019		-

Stock-Based Compensation Expense Recognized

Total stock-based compensation expense recognized by function was as follows (in thousands):

	Year Ended December 31,
	2019		2018		2017
Research and development	$	1,777	$	842	$	93
General and administrative		2,230		1,151		110
Total stock-based compensation expense	$	4,007	$	1,993	$	203

Fair Value of Employee Stock Options Granted and ESPP Rights to Purchase Common Stock Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions

	Options							ESPP Rights
	Year Ended December 31,							Year Ended December 31,
	2019		2018		2017			2019		2018			2017
Expected term (years)	5.8 - 5.9		5.5 - 6.1			6.1			0.5		0.5			—
Expected volatility	78.7 - 83.7%		82.0 - 83.2%			89.8	%	73.7 - 109.9%			74.3	%		—
Risk-free interest rate	1.5 - 2.6%		2.6 - 3.1%			2.0	%	1.6 - 2.4%			2.5	%		—
Expected dividend yield		—		—		—			—		—			—

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Domestic and Foreign Components of Net Loss

The following table presents domestic and foreign components of net loss for the periods presented (in thousands):

	Year Ended December 31,
	2019			2018			2017
Domestic	$	(34,181	)	$	(23,047	)	$	(7,551	)
Foreign		(906	)		(120	)		(966	)
Total	$	(35,087	)	$	(23,167	)	$	(8,517	)

Schedule of Effective Tax Rate of Provision for Income Taxes Differs From Federal Statutory Rate

The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows:

	Year Ended December 31,
	2019				2018				2017
Federal statutory income tax rate		21.0		%		21.0		%		34.0		%
State taxes, net of federal benefit		0.9				6.4				6.0
Foreign tax rate differential		0.2				0.1				(0.5	)
Permanent differences		(1.7	)			0.3				(3.8	)
Research and development credit		1.9				1.4				2.5
Federal rate change impact		0.0				0.0				(31.4	)
Change in valuation allowance		(22.3	)			(29.2	)			(6.8	)
Provision for income taxes		—		%		—		%		—		%

Schedule of Components of Deferred Tax Assets and Liabilities

The components of the deferred tax assets and liabilities are as follows (in thousands):

	Year Ended December 31,
	2019			2018			2017
Deferred tax assets
Reserves and accruals	$	1,056		$	1,009		$	169
Net operating loss carryforwards		16,986			10,985			6,802
Research and development credit carryforwards		2,177			1,194			515
Lease Liabilities		1,336			—			—
Gross deferred tax assets		21,555			13,188			7,486
Valuation allowance		(20,196	)		(12,560	)		(7,434	)
Net deferred tax assets		1,359			628			52
Deferred tax liabilities
Property and equipment		(557	)		(628	)		(52	)
Right-of-use asset		(802	)		—			—
Net deferred tax	$	—		$	—		$	—

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Calculation of Basic and Diluted Net Loss per Share

The following table sets forth the calculation of basic and diluted net loss per share during the periods presented (in thousands, except share and per share data):

	Year Ended December 31,
	2019			2018			2017
Numerator:
Net loss	$	(35,087	)	$	(23,167	)	$	(8,517	)
Denominator:
Weighted-average shares of common stock outstanding		19,083,826			10,264,584			599,291
Net loss per share, basic and diluted	$	(1.84	)	$	(2.26	)	$	(14.21	)

Anti-dilutive Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share

	Year Ended December 31,
	2019		2018		2017
Redeemable convertible preferred stock on an if converted basis		—		—		12,263,126
Options to purchase common stock		3,107,066		2,181,466		1,213,010
Common stock subject to future vesting		30,027		89,257		238,618
Total		3,137,093		2,270,723		13,714,754

Selected Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Schedule of Selected Quarterly Financial Information (Unaudited)

The following amounts are in thousands, except per share amounts:

	Quarter Ended
(in thousands, except per share amounts)	March 31, 2019			June 30, 2019			September 30, 2019			December 31, 2019
	(Unaudited)
Operating expenses	$	8,309		$	9,355		$	9,681		$	9,997
Net loss	$	(7,642	)	$	(8,718	)	$	(9,148	)	$	(9,579	)
Net loss per share, basic and diluted	$	(0.40	)	$	(0.46	)	$	(0.48	)	$	(0.50	)

	Quarter Ended
(in thousands, except per share amounts)	March 31, 2018			June 30, 2018			September 30, 2018			December 31, 2018
	(Unaudited)
Operating expenses	$	5,086		$	6,950		$	6,264		$	6,426
Net loss	$	(4,947	)	$	(6,775	)	$	(5,663	)	$	(5,782	)
Net loss per share, basic and diluted	$	(6.53	)	$	(3.31	)	$	(0.30	)	$	(0.30	)

Organization and Description of the Business - Additional Information (Details) $ / shares in Units, $ in Thousands				12 Months Ended
	Feb. 04, 2020 USD ($) $ / shares shares	Jun. 25, 2018 USD ($) $ / shares shares	Jun. 08, 2018 $ / shares	Dec. 31, 2019 USD ($) Segment shares	Dec. 31, 2018 USD ($) shares
Organization And Description Of Business [Line Items]
Number of operating segments \| Segment				1
Stockholders equity, reverse stock split			1-for-5.62
Stockholders equity, stock split, conversion ratio			0.1779
Minimum price post-split \| $ / shares			$ 15.884
Adjusted price post split \| $ / shares			$ 7.942
Net proceeds from issuance of common stock \| $					$ 77,695
Common stock, shares authorized				125,000,000	125,000,000
Preferred stock, shares authorized				10,000,000	10,000,000
Accumulated deficit \| $				$ 84,282	$ 49,195
Minimum
Organization And Description Of Business [Line Items]
Sufficient cash and cash equivalents available period term				12 months
IPO
Organization And Description Of Business [Line Items]
Common stock, shares, issued		5,750,000
Common stock, shares issued, price per share \| $ / shares		$ 15.00
Net proceeds from issuance of common stock \| $		$ 77,700
Payments of stock issuance costs \| $		$ 8,600
Convertible preferred stock converted into common stock		12,263,126
Overallotment Option
Organization And Description Of Business [Line Items]
Common stock, shares, issued		750,000
Underwritten Public Offering \| Subsequent Event
Organization And Description Of Business [Line Items]
Common stock, shares, issued	18,965,385
Common stock, shares issued, price per share \| $ / shares	$ 2.60
Net proceeds from issuance of common stock \| $	$ 53,300

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 14,951	$ 24,182	$ 51,033
Restricted cash			13
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$ 14,951	$ 24,182	$ 51,046	$ 9,760

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Impairment losses	$ 0
Reduction of research and development expenses	635,000	$ 5,000	$ 499,000
Research and development tax credit receivable	642,000	$ 5,000
Interest charges or penalties related to unrecognized tax benefits	$ 0
Furniture, Laboratory and Office Equipment \| Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets	5 years
Furniture, Laboratory and Office Equipment \| Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets	7 years
Computer Equipment
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets	3 years
Australia
Summary Of Significant Accounting Policies [Line Items]
Concentrations of credit risk	$ 200,000

Summary of Significant Accounting Policies - Impact of Accounting Pronouncements Adoption on Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Operating lease ROU asset	$ 3,817	$ 4,236
Operating lease liabilities, current	900	774
Operating lease liabilities, noncurrent	$ 5,464	$ 6,364
Deferred rent, current			$ 354
Deferred rent, noncurrent			$ 2,548

Fair Value Measurements - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Transfers from Level 1 to Level 2	$ 0	$ 0
Transfers from Level 2 to Level 1	$ 0	$ 0

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 77,986	$ 106,406
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	20,016	48,848
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	57,970	57,558
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	14,731	23,156
Money Market Funds \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	14,731	23,156
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	5,285	25,692
U.S. Treasury Securities \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	5,285	25,692
Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	15,186	19,190
Commercial paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	15,186	19,190
Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	17,171	20,451
Corporate debt securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	17,171	20,451
U.S. agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	25,613	17,917
U.S. agency bonds \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 25,613	$ 17,917

Available-for-Sale Securities - Summary of Available-For-Sale Securities Recorded in Cash and Cash Equivalents or Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 77,955
Fair Value	77,986
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	77,955	$ 106,427
Unrealized Gains	32	4
Unrealized Losses	(1)	(25)
Fair Value	77,986	106,406
Fair Value, Measurements, Recurring \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	14,731	23,156
Fair Value	14,731	23,156
Fair Value, Measurements, Recurring \| U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	5,285	25,698
Unrealized Gains	1
Unrealized Losses	(1)	(6)
Fair Value	5,285	25,692
Fair Value, Measurements, Recurring \| Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	15,174	19,203
Unrealized Gains	12
Unrealized Losses		(13)
Fair Value	15,186	19,190
Fair Value, Measurements, Recurring \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	17,168	20,449
Unrealized Gains	3	4
Unrealized Losses		(2)
Fair Value	17,171	20,451
Fair Value, Measurements, Recurring \| U.S. agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	25,597	17,921
Unrealized Gains	16
Unrealized Losses		(4)
Fair Value	$ 25,613	$ 17,917

Available-for-Sale Securities - Summary of Amortized Cost and Estimated Fair Value of Available-for-sale Securities by Contractual Maturity (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Available-for-sale securities maturing, Amortized Cost:
In one year or less, Amortized Cost	$ 77,955
Amortized Cost	77,955
Available-for-sale securities maturing, Estimated Fair Value:
In one year or less, Estimated Fair Value	77,986
Total available-for-sale securities, Estimated Fair Value	$ 77,986

Available-for-Sale Securities - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 USD ($)
Investments Debt And Equity Securities [Abstract]
Sale of available-for-sale securities	$ 0

Balance Sheet Components - Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 6,099	$ 5,530
Less accumulated depreciation and amortization	(1,817)	(935)
Property and equipment, net	4,282	4,595
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	3,268	3,268
Furniture, Laboratory and Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	2,578	2,043
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 253	$ 219

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Depreciation expense	$ 0.9	$ 0.7	$ 0.2

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accrued preclinical and research costs	$ 1,687	$ 1,146
Accrued clinical costs	1,027	434
Accrued employee-related costs	1,293	736
Accrued professional services	53	138
Other	158	224
Total accrued liabilities	$ 4,218	$ 2,678

Lease - Additional Information (Details) $ in Thousands	12 Months Ended
Lease - Additional Information (Details) $ in Thousands	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Operating lease existence of option to extend [true false]	true
Operating lease, option to extend	The operating lease agreement has one option to extend the lease term for a period of five years at the fair market rate at the time of the extension.
Operating lease, renewal term	5 years
Weighted average remaining lease term	5 years 2 months 1 day
Operating lease liability, weighted average discount rate	10.00%
Rent expense	$ 1,100	$ 1,000	$ 300
Variable lease costs	$ 505	$ 400	$ 100
South San Francisco, California [Member]
Area of lease \| ft²	24,357
Lease commenced date	Mar. 01, 2018
Lease expiration date	Feb. 28, 2025

Lease - Details of Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Lessee Disclosure [Abstract]
Cash paid for operating lease liabilities	$ 774
Operating lease costs	1,099
Variable lease costs	505	$ 400	$ 100
ROU asset obtained in exchange for operating lease obligation	4,236
2020	1,497
2021	1,542
2022	1,588
2023	1,635
2024	1,684
Thereafter	282
Total undiscounted lease payments	8,228
Less: imputed interest	(1,864)
Total lease liabilities	6,364
Operating lease liabilities, current	900			$ 774
Operating lease liabilities, noncurrent	5,464			$ 6,364
Total operating lease liabilities	$ 6,364

Lease - Schedule of Future Minimum Lease Payments Under Noncancelable Facility Operating Lease (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Year ending December 31:
2019	$ 1,453
2020	1,497
2021	1,542
2022	1,588
2023	1,635
2024	1,684
Thereafter	282
Total future minimum lease payments	$ 9,681

Redeemable Convertible Preferred Stock - Additional Information (Details)	1 Months Ended
	Jun. 30, 2018 shares
IPO
Temporary Equity [Line Items]
Number of outstanding shares of convertible preferred stock converted into common stock	12,263,126

Stock-Based Compensation - Additional Information (Details)		12 Months Ended
	Jun. 25, 2018 shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) ExecutiveOfficer $ / shares shares	Dec. 31, 2017 USD ($)	Jun. 30, 2018 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted		1,248,871
Maximum number of shares issued upon exercise of incentive stock options		1,478,773
Common stock, shares issued		19,208,077	19,114,421
Weighted average grant date fair value of options granted \| $ / shares		$ 13.36
Aggregate intrinsic value of exercised stock options \| $		$ 292,000
Period for right to purchase underlying option shares lapses after applicable vesting commencement date		1 year
Stock-based compensation expense recognized \| $		$ 4,007,000	$ 1,993,000	$ 203,000
Payments of dividends of common stock \| $		$ 0
Expected dividend yield		0.00%
Early Exercise Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			36 months
Nonvested common shares outstanding		30,027	68,349
Percentage of underlying option shares whose right to purchase lapses after applicable vesting commencement date			25.00%
Right to repurchase shares underlying shares			0.0208
Other Current Liabilities \| Early Exercise Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued upon early exercise of stock options are subject to repurchase \| $		$ 62,000	$ 112,000
Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost \| $		$ 10,300,000
Estimated weighted average amortization period		2 years 6 months
Expected term				6 years 1 month 6 days
Employee options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term		5 years 10 months 24 days	6 years 1 month 6 days
Employee options \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term		5 years 9 months 18 days	5 years 6 months
Stock Options Granted to Employees that Contain Performance Condition
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted		0	115,657
Stock-based compensation expense recognized \| $			$ 474,000
Number of executive officers granted with purchase option \| ExecutiveOfficer			2
Number of option vested	115,657
Options vesting date			Jun. 25, 2018
Stock-based compensation expense recognition period			2018-06
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		4 years
Nonvested common shares outstanding			20,908
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term		6 months	6 months
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future issuance		1,765,266
Number of shares will increase automatically through every year on specified date		--01-01
Number of shares increase automatically continuing through maximum period		beginning on January 1, 2019 and continuing through and including January 1, 2028
2018 Equity Incentive Plan \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares authorized available for issuance		1,600,692
Increase in number of shares reserved for issuance as percentage of total number of shares of capital stock outstanding on last date of preceding calendar year		5.00%
2018 Equity Incentive Plan \| Maximum \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares authorized available for issuance		4,000,000
2018 Equity Incentive Plan \| Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted		1,271,992
2018 Equity Incentive Plan \| Incentive Stock Options \| Maximum \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares issued upon exercise of incentive stock options		12,500,000
2018 Equity Incentive Plan \| Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of RSU granted		0	10,189
Weighted-average estimated grant-date fair value \| $ / shares			$ 17.75
Stock-based compensation expense recognized \| $			$ 181,000
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		4 years
Options to purchase of common stock outstanding		1,835,074
Weighted average grant date fair value of options granted \| $ / shares		$ 9.33	$ 4.23
Aggregate intrinsic value of exercised stock options \| $		$ 292,000	$ 370,000
2015 Equity Incentive Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted expiry period		10 years
2018 Employee Stock Purchase Plan \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future issuance		364,488			200,000
Common stock, shares issued		26,656
Authorized an offering beginning period		Nov. 16, 2018
Authorized an offering ending period		May 15, 2019
Authorized an new offering beginning period		May 16, 2019
Authorized an new offering ending period		Nov. 16, 2019
2018 Employee Stock Purchase Plan \| Maximum \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of annual increase in number of common stock shares		1.00%
Annual increase in number of common stock shares		375,000
Option price per share of common stock at fair market value		85.00%

Stock-Based Compensation - Summary of Activity under Stock Option Plans and Related Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of options outstanding, Outstanding, Beginning balance	2,181,466
Number of options outstanding, Options granted	1,248,871
Number of options outstanding, Options exercised	(67,000)
Number of options outstanding, Options cancelled	(256,271)
Number of options outstanding, Outstanding, Ending balance	3,107,066	2,181,466
Number of options outstanding, options vested and exercisable	1,478,773
Weighted average exercise price, Outstanding, Beginning balance	$ 3.80
Weighted average exercise price, Options granted	13.36
Weighted average exercise price, Options exercised	0.90
Weighted average exercise price, Options cancelled	10.04
Weighted average exercise price, Outstanding, Ending balance	7.19	$ 3.80
Weighted average exercise price, options vested and exercisable	$ 4.59
Weighted average remaining contractual term, (Years) Outstanding, Beginning balance	8 years 2 months 12 days	8 years 6 months
Weighted average remaining contractual term, (Years) options vested and exercisable	7 years 4 months 24 days
Aggregate intrinsic value, Outstanding	$ 3,151	$ 43,189
Aggregate intrinsic value, Options exercised	292
Aggregate intrinsic value, options vested and exercisable	$ 2,322

Stock-Based Compensation - Summarizes of Activity of Nonvested Restricted Stock (Details) - Restricted Stock	12 Months Ended
	Dec. 31, 2019 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested beginning balance	20,908
Number of Shares Outstanding, Vested	(20,908)

Stock-Based Compensation - Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 4,007	$ 1,993	$ 203
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,777	842	93
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,230	$ 1,151	$ 110

Stock-Based Compensation - Fair Value of Employee Stock Options Granted and ESPP Rights to Purchase Common Stock Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield	0.00%
Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)			6 years 1 month 6 days
Expected volatility			89.80%
Risk-free interest rate			2.00%
ESPP Rights
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 months	6 months
Expected volatility		74.30%
Risk-free interest rate		2.50%
Minimum \| Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 9 months 18 days	5 years 6 months
Expected volatility, Minimum	78.70%	82.00%
Risk-free interest rate, Minimum	1.50%	2.60%
Minimum \| ESPP Rights
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, Minimum	73.70%
Risk-free interest rate, Minimum	1.60%
Maximum \| Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 10 months 24 days	6 years 1 month 6 days
Expected volatility, Maximum	83.70%	83.20%
Risk-free interest rate, Maximum	2.60%	3.10%
Maximum \| ESPP Rights
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, Maximum	109.90%
Risk-free interest rate, Maximum	2.40%

License Agreement - Additional Information (Details)	1 Months Ended
License Agreement - Additional Information (Details)	Jun. 30, 2015 USD ($)
License Agreement \| Amgen, Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum future payments upon achievement of certain development and commercial milestones	$ 172,500,000

Defined Contribution Plan - Additional Information (Details) - Savings and Investment Plan - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Employees contributions amount up to lesser of pre-tax compensation	$ 56,000
Percentage of employees contributions amount up to lesser of pre-tax compensation	100.00%
Employer match of per contribution towards participants contribution	$ 1.00
Participants of plan per contribution	1.00
Employer incurred matching contribution expenses	$ 249,000	$ 167,000	$ 77,000
Maximum
Defined Contribution Plan Disclosure [Line Items]
Employer match of employees contributions in amount in percentage	4.00%

Income Taxes - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes Disclosure [Line Items]
Provision for income taxes		$ 0	$ 0	$ 0
Research and development tax credit utilized against employer's portion of payroll tax	$ 250,000
Research and development tax credit utilized as reduction of payroll expenses		284,000	175,000
Valuation allowance increased		7,600,000	$ 5,100,000	$ 400,000
Benefit for deferred tax assets		0
Liability related to uncertain tax positions		0
Interest charges or penalties related to unrecognized tax benefits		0
Accrued interest and penalties related to gross unrecognized tax benefits		0
Australian Taxation Office
Income Taxes Disclosure [Line Items]
Net operating loss (NOL) carryforwards		1,900,000
Federal
Income Taxes Disclosure [Line Items]
Net operating loss (NOL) carryforwards		$ 72,700,000
Net operating loss carryforwards expiration start year		2035
Net operating loss (NOL) carryforwards indefinite		$ 50,600,000
Federal \| Research and Development
Income Taxes Disclosure [Line Items]
Tax credit carryforward expiration start year		2035
Tax credit carryforward		$ 1,300,000
State
Income Taxes Disclosure [Line Items]
Net operating loss (NOL) carryforwards		$ 17,300,000
Net operating loss carryforwards expiration start year		2035
State \| Research and Development
Income Taxes Disclosure [Line Items]
Tax credit carryforward		$ 1,100,000

Income Taxes - Schedule of Domestic and Foreign Components of Net Loss (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Net loss	$ (9,579)	$ (9,148)	$ (8,718)	$ (7,642)	$ (5,782)	$ (5,663)	$ (6,775)	$ (4,947)	$ (35,087)	$ (23,167)	$ (8,517)
Domestic
Operating Loss Carryforwards [Line Items]
Net loss									(34,181)	(23,047)	(7,551)
Foreign
Operating Loss Carryforwards [Line Items]
Net loss									$ (906)	$ (120)	$ (966)

- Definition

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

+ References + Details

Income Taxes - Schedule of Effective Tax Rate of Provision for Income Taxes Differs From Federal Statutory Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Federal statutory income tax rate	21.00%	21.00%	34.00%
State taxes, net of federal benefit	0.90%	6.40%	6.00%
Foreign tax rate differential	0.20%	0.10%	(0.50%)
Permanent differences	(1.70%)	0.30%	(3.80%)
Research and development credit	1.90%	1.40%	2.50%
Federal rate change impact	0.00%	0.00%	(31.40%)
Change in valuation allowance	(22.30%)	(29.20%)	(6.80%)

Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Reserves and accruals	$ 1,056	$ 1,009	$ 169
Net operating loss carryforwards	16,986	10,985	6,802
Research and development credit carryforwards	2,177	1,194	515
Lease Liabilities	1,336
Gross deferred tax assets	21,555	13,188	7,486
Valuation allowance	(20,196)	(12,560)	(7,434)
Net deferred tax assets	1,359	628	52
Deferred tax liabilities
Property and equipment	(557)	$ (628)	$ (52)
Right-of-use asset	$ (802)

Net Loss Per Share - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss	$ (9,579)	$ (9,148)	$ (8,718)	$ (7,642)	$ (5,782)	$ (5,663)	$ (6,775)	$ (4,947)	$ (35,087)	$ (23,167)	$ (8,517)
Denominator:
Weighted-average shares of common stock outstanding									19,083,826	10,264,584	599,291
Net loss per common share, basic and diluted	$ (0.50)	$ (0.48)	$ (0.46)	$ (0.40)	$ (0.30)	$ (0.30)	$ (3.31)	$ (6.53)	$ (1.84)	$ (2.26)	$ (14.21)

- Definition

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

+ References + Details

Net Loss Per Share - Anti-dilutive Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	3,137,093	2,270,723	13,714,754
Redeemable Convertible Preferred Stock on an if Converted Basis
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share			12,263,126
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	3,107,066	2,181,466	1,213,010
Common stock subject to future vesting [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	30,027	89,257	238,618

Selected Quarterly Financial Information (Unaudited) - Schedule of Selected Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Operating expenses	$ 9,997	$ 9,681	$ 9,355	$ 8,309	$ 6,426	$ 6,264	$ 6,950	$ 5,086	$ 37,342	$ 24,726	$ 8,749
Net loss	$ (9,579)	$ (9,148)	$ (8,718)	$ (7,642)	$ (5,782)	$ (5,663)	$ (6,775)	$ (4,947)	$ (35,087)	$ (23,167)	$ (8,517)
Net loss per common share, basic and diluted	$ (0.50)	$ (0.48)	$ (0.46)	$ (0.40)	$ (0.30)	$ (0.30)	$ (3.31)	$ (6.53)	$ (1.84)	$ (2.26)	$ (14.21)

- Definition

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

+ References + Details

Subsequent Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Feb. 04, 2020	Dec. 31, 2018
Subsequent Event [Line Items]
Net proceeds from the public offering		$ 77,695
Underwritten Public Offering \| Subsequent Event
Subsequent Event [Line Items]
Common stock, shares, issued	18,965,385
Pre funded warrants to purchase shares of common stock	2,884,615
Common stock, shares issued, price per share	$ 2.60
Warrant issue price per share	$ 2.599
Net proceeds from the public offering	$ 53,300
Underwritten Public Offering \| Subsequent Event \| Existing Stockholder, Morningside Ventures and certain officers and directors
Subsequent Event [Line Items]
Net proceeds from the public offering	$ 22,900