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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2018	Mar. 22, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
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	Non-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		19,118,421
Entity Public Float			$ 267

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 24,182	$ 51,033
Marketable securities	83,250
Prepaid expenses	1,884	785
Other current assets	489	508
Total current assets	109,805	52,326
Restricted cash		13
Property and equipment, net	4,595	1,540
Other assets	282	343
Total assets	114,682	54,222
Current liabilities:
Accounts payable	193	547
Accrued liabilities	2,678	911
Deferred rent, current	354
Other liabilities, current	112	26
Total current liabilities	3,337	1,484
Deferred rent, noncurrent	2,548	494
Total liabilities	5,885	1,978
Redeemable convertible preferred stock, $0.001 par value, zero and 75,533,240 shares authorized as of December 31, 2018 and 2017, respectively; zero and 12,263,126 shares issued and outstanding as of December 31, 2018 and 2017, respectively		77,931
Stockholders' equity (deficit):
Common stock, $0.001 par value, 125,000,000 and 96,000,000 shares authorized as of December 31, 2018 and 2017, respectively; 19,114,421 and 948,578 shares issued and outstanding as of December 31, 2018 and 2017, respectively	19	1
Preferred stock, $0.001 par value, 10,000,000 and zero shares authorized as of December 31, 2018 and 2017, respectively; zero shares issued and outstanding as of December 31, 2018 and 2017
Additional paid-in capital	158,176	451
Accumulated other comprehensive loss	(203)	(111)
Accumulated deficit	(49,195)	(26,028)
Total stockholders' equity (deficit)	108,797	(25,687)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 114,682	$ 54,222

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Redeemable convertible preferred stock, par value	$ 0.001	$ 0.001
Redeemable convertible preferred stock, shares authorized	0	75,533,240
Redeemable convertible preferred stock, shares issued	0	12,263,126
Redeemable convertible preferred stock, shares outstanding	0	12,263,126
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	96,000,000
Common stock, shares issued	19,114,421	948,578
Common stock, shares outstanding	19,114,421	948,578
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development	$ 18,136	$ 6,469	$ 7,373
General and administrative	6,590	2,280	1,617
Total operating expenses	24,726	8,749	8,990
Loss from operations	(24,726)	(8,749)	(8,990)
Interest income	1,559	232
Net loss	$ (23,167)	$ (8,517)	$ (8,990)
Net loss per common share, basic and diluted	$ (2.26)	$ (14.21)	$ (26.56)
Weighted-average shares used to compute net loss per common share, basic and diluted	10,264,584	599,291	338,446

- 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (23,167)	$ (8,517)	$ (8,990)
Other comprehensive (loss) income, net of tax:
Foreign currency translation adjustments	(72)	39	(150)
Unrealized loss on marketable securities	(20)
Total other comprehensive (loss) income, net of tax	(92)	39	(150)
Comprehensive loss	$ (23,259)	$ (8,478)	$ (9,140)

- 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, 2015	$ (8,416)		$ 1	$ 104		$ (8,521)
Balance, shares at Dec. 31, 2015			911,151
Balance at Dec. 31, 2015		$ 28,176
Balance, shares at Dec. 31, 2015		5,966,753
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options, shares			37,427
Stock-based compensation expense	128			128
Other comprehensive loss	(150)				$ (150)
Net loss	(8,990)					(8,990)
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 common shares issued pursuant to early exercises	16			16
Stock-based compensation expense	203			203
Other comprehensive 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	$ 77,931
Balance, shares at Dec. 31, 2017	12,263,126	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 upon exercise of stock options, net of amount related to early exercised options	$ 55			55
Issuance of common stock upon exercise of stock options, net of amount related to early exercised options, shares	142,528		142,528
Issuance of common stock upon vesting of restricted stock units			10,189
Vesting related to common shares issued pursuant to early exercises	$ 69			69
Stock-based compensation expense	1,993			1,993
Other comprehensive 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
Balance at Dec. 31, 2018		$ 0
Balance, shares at Dec. 31, 2018	0	0

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (23,167)	$ (8,517)	$ (8,990)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	690	175	154
Stock-based compensation	1,993	203	128
Amortization of premiums and discounts on marketable securities	(476)
Loss on disposal of property and equipment	106
Changes in operating assets and liabilities
Prepaid expenses & other current assets	(1,136)	(543)	(598)
Other assets	61	(282)
Accounts payable & accrued liabilities	1,440	844	(469)
Other liabilities, current	(8)	6
Deferred rent	(295)	5	15
Net cash used in operating activities	(20,792)	(8,109)	(9,760)
Cash flows from investing activities:
Purchases of property and equipment	(1,120)	(389)	(132)
Purchases of marketable securities	(119,244)
Maturities of marketable securities	36,450
Proceeds from sale of property and equipment	10
Net cash used in investing activities	(83,904)	(389)	(132)
Cash flows from financing activities:
Proceeds from initial public offering, net of issuance costs	77,695
Proceeds from issuance of preferred stock, net of issuance costs		49,755
Proceeds from the exercise of stock options	218		36
Net cash provided by financing activities	77,913	49,755	36
Effect of exchange rate changes on cash and cash equivalents and restricted cash	(81)	29	(150)
Net (decrease) increase in cash, cash equivalents and restricted cash	(26,864)	41,286	(10,006)
Cash, cash equivalents and restricted cash at the beginning of period	51,046	9,760	19,766
Cash, cash equivalents and restricted cash at the end of period	24,182	51,046	$ 9,760
Supplemental disclosures of noncash financing information:
Reclassification of employee stock liability to equity upon vesting	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, 2018

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 $49.2 million as of December 31, 2018. 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 existing cash, cash equivalents and marketable securities 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, 2018

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 (“U.S. 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 U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities 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 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 and 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,
	2018		2017		2016
Cash and cash equivalents	$	24,182	$	51,033	$	9,747
Restricted cash		—		13		13
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$	24,182	$	51,046	$	9,760

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. The majority of the Company’s cash, cash equivalents and marketable securities are held by financial institutions in the United States, while approximately $1.0 million is 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, 2018, 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.

Fair Value of Financial Instruments

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, restricted cash, 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 does not have any assets or liabilities measured using Level 3 inputs as of December 31, 2018 and 2017.

The following table summarizes our financial assets measured at fair value on a recurring basis (in thousands):

	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		—
Government agency bonds		17,917		—		17,917		—
Total	$	106,406	$	48,848	$	57,558	$	—

	December 31, 2017
	Total		Level 1		Level 2		Level 3
Financial Assets:
Money market funds	$	50,242	$	50,242	$	—	$	—
Total	$	50,242	$	50,242	$	—	$	—

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 $5,000, $499,000 and $385,000 as a reduction of research and development expenses for the years ended December 31, 2018, 2017 and 2016, respectively, in connection with the research and development tax incentive from the ATO. As of December 31, 2018 and 2017, the research and development tax credit receivable was $5,000 and $498,000, respectively, which is included in other current assets in the consolidated balance sheets.

Stock-Based Compensation

Stock-based awards issued to employees and directors, 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.

Stock-based awards and stock options issued to nonemployee consultants are recorded at fair value as of the grant date using the Black-Scholes option pricing model. The unearned portion of the stock-based compensation is remeasured at each reporting period using the Black-Scholes option pricing model, and the resulting change in fair value is recognized in the statements of operations over the remaining period the related services are rendered.

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 2018

In May 2017, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2017-09, Compensation – Stock Compensation (Topic 718): Scope of Modification Accounting. This ASU provides guidance about which changes to the terms or conditions of a share-based payment award requires the Company to apply modification accounting. This ASU will be effective for the Company for annual reporting periods, including interim reporting periods, beginning after December 15, 2017. The Company adopted this standard on January 1, 2018 noting it did not have a material impact on the Company’s financial statements.

New Accounting Pronouncements Not Yet Adopted

Leases (Topic 842)

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). 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 expects to adopt the new standard on January 1, 2019 and use the effective date as its date of initial application. Consequently, financial information will not be updated and the disclosures required under the new standard will not be provided for dates and periods before January 1, 2019.

The Company expects that this standard will have a material effect on its financial statements. While the Company continues to assess all of the effects of adoption, it currently believes the most significant effects relate to (1) the recognition of new right-of-use (ROU) assets and lease liabilities on its balance sheet for its operating lease for its headquarters at 4000 Shoreline Court, South San Francisco; and (2) providing significant new disclosures about its leasing activities.

On adoption, the Company currently expects to recognize an operating lease liability of approximately $7.1 million based on the present value of the remaining minimum rental payments under current leasing standards for existing operating leases. The operating lease ROU asset of approximately $4.2 million consists of the amount of the initial measurement of lease liability, net of the unamortized lease incentives previously received of approximately $2.9 million that are currently recorded as deferred rent liabilities on its consolidated balance sheet.

The new standard also provides practical expedients for an entity’s ongoing accounting. The Company currently expects to elect 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 will not elect the practical expedient to not separate lease and non-lease components for all of its leases.

Other recent accounting announcements

In June 2016, FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326), or ASU 2016-13. ASU 2016-13 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 is currently evaluating the potential impact of the adoption of this guidance on its financial statements.

In June 2018, the FASB issued ASU 2018-07, Compensation – Stock Compensation (Topic 718). ASU 2018-07 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 has evaluated the potential impact of this guidance and does not believe that it will have a material impact on the Company’s financial statements.

In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement, 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 is currently evaluating the effect the new guidance will have on its consolidated financial statements.

In August 2018, the SEC adopted amendments to certain disclosure requirements in Securities Act Release No. 33-10532, Disclosure Update and Simplification. Among the amendments is the requirement to present the changes in stockholders’ equity in the interim financial statements included in quarterly reports on Form 10-Q. The amendments are effective for all filings made on or after November 5, 2018. However, registrants may begin providing the new interim reconciliations of stockholders' equity in the Form 10-Q for the interim period beginning after the effective date. The Company plans to implement the changes required by these amendments to its Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) in its Form 10-Q filing for the period ended March 31, 2019.

Cash Equivalents and Marketable Securities

12 Months Ended

Dec. 31, 2018

Cash And Cash Equivalents [Abstract]

Cash Equivalents and Marketable Securities

3. Cash Equivalents and Marketable Securities

As of December 31, 2018 and 2017, financial assets and liabilities measured and recognized at fair value on a recurring basis and classified under the appropriate level of the fair value hierarchy as described above were as follows (in thousands):

	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
Government agency bonds		17,921		—		(4	)		17,917
Total	$	106,427	$	4	$	(25	)	$	106,406

	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Financial Assets:
Money market funds	$	50,242	$	—	$	—	$	50,242
Total	$	50,242	$	—	$	—	$	50,242

As of December 31, 2018, 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
Marketable securities maturing:
In one year or less	$	83,270	$	83,250
Total marketable securities	$	83,270	$	83,250

The Company determined that the gross unrealized losses on its marketable securities as of December 31, 2018 were temporary in nature. 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, 2018. There were no sales of available-for-sale securities in any of the periods presented.

Balance Sheet Components

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Balance Sheet Components

4. Balance Sheet Components

Property and Equipment, Net

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

	December 31, 2018			December 31, 2017
Leasehold improvements	$	3,268		$	155
Furniture, laboratory and office equipment		2,043			1,242
Computer equipment		219			34
Construction in progress		—			464
Total property and equipment		5,530			1,895
Less accumulated depreciation and amortization		(935	)		(355	)
Property and equipment, net	$	4,595		$	1,540

Under the terms of its lease for office and laboratory space at 4000 Shoreline Court, South San Francisco, the Company received an incentive from the landlord for $3.2 million to construct leasehold improvements, which have been recorded in fixed assets and as deferred rent in other liabilities that will be amortized over the remaining lease term.

Depreciation expense was $0.7 million for the year ended December 31, 2018, $0.2 million for the year ended December 31, 2017 and $0.2 million for the year ended December 31, 2016.

Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	December 31, 2018		December 31, 2017
Accrued preclinical and research costs	$	1,146	$	108
Accrued clinical costs		434		340
Accrued employee-related costs		736		422
Accrued professional services		138		—
Other		224		41
Accrued liabilities	$	2,678	$	911

Redeemable Convertible Preferred Stock

12 Months Ended

Dec. 31, 2018

Temporary Equity Disclosure [Abstract]

Redeemable Convertible Preferred Stock

5. 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, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

6. 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 will 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 for the purchase of that number of shares of common stock. As of December 31, 2018, 85,621 options to purchase common stock and 10,189 RSUs have been granted and 1,802,145 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 that may be issued pursuant to stock awards under the 2018 Plan will not exceed 4,000,000 shares, which is the sum of (i) 1,600,692 shares plus (ii) the number of shares reserved, and remaining 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 will automatically increase on January 1 of each year, 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. 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 Equity Incentive 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, 2018, options to purchase 2,095,845 shares of common stock were outstanding under the 2015 Plan.

2018 Employee Stock Purchase Plan

In June 2018, the Company’s board of directors 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 the first day of each year beginning in 2019 and ending in 2028, in each case subject to the approval of the board of directors, 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; provided, that prior to the date of any such increase, the board of directors may determine that such increase will be less than the amount set forth in clauses (i) and (ii). As of December 31, 2018, no shares of common stock had been issued under the ESPP and 200,000 shares remained available for future issuance under the ESPP. The option price per share of common stock to be paid by a participant upon exercise of the participant’s option on the applicable exercise date for an offering period shall be equal to 85% of the lesser of the fair market value of a share of common stock on (a) the applicable grant date or (b) the applicable exercise date. The Board authorized an initial offering beginning on November 16, 2018 and ending on May 15, 2019. Following the end of the initial offering, a new offering will automatically begin on the day that immediately follows the conclusion of the preceding offering.

Stock Option Activity

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

	Number of Options Outstanding			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at December 31, 2017		1,213,010		$	1.54		8.7	$	999
Options granted		1,121,901		$	5.93
Options exercised		(142,528	)	$	1.54			$	370
Options cancelled		(10,917	)	$	0.90
Outstanding at December 31, 2018		2,181,466		$	3.80		8.5	$	43,189
Vested and exercisable at December 31, 2018		833,679		$	2.00		7.7	$	18,008

The weighted average grant date fair value of options granted during the years ended December 31, 2018 and 2017 was $4.23 and $1.61 per share, respectively. The 2015 Plan allows for early exercisable option grants, which permit the grantee to exercise a stock option in exchange for stock before the requisite service is provided (e.g., before the award is vested under its original terms); however, such arrangements permit the Company to subsequently repurchase such shares at the exercise price if the vesting conditions are not satisfied. To date, the Company has made such grants only to non-employee board members. The total intrinsic value of exercised stock options during the years ended December 31, 2018 and 2017 was $370,000 and $0, 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 Purchase Agreements

As of December 31, 2018 and 2017, there were 68,349 and 45,224, respectively, of nonvested common shares outstanding that were exercised early and 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 after the applicable vesting commencement date and 1/48 of the shares underlying the original grant per 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. As of December 31, 2018 and 2017, the Company recorded in other current liabilities $112,000 and $18,000, 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 for 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, 2017.

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, 2017.

Restricted Stock

In addition to the nonvested common shares outstanding described above at “Early Exercise Stock Purchase Agreements,” 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 activity of nonvested restricted stock:

	Number of Shares
Nonvested—December 31, 2017		193,394
Vested		(172,486	)
Nonvested—December 31, 2018		20,908

Stock-Based Compensation Expense

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

	Year Ended December 31,
	2018		2017		2016
General and administrative	$	1,151	$	110	$	64
Research and development		842		93		64
Total stock-based compensation expense	$	1,993	$	203	$	128

As of December 31, 2018, the unrecognized stock-based compensation cost and the estimated weighted average amortization period, using the straight-line attribution method, was as follows (dollars in thousands):

	Unrecognized Compensation Cost		Weighted Average Remaining Amortization Period (Years)
Employee options	$	3,977		2.8
Nonemployee options		4		0.4
Total unrecognized stock-based compensation expense	$	3,981

The fair value of the employee stock options granted is calculated using the Black-Scholes option-pricing model with the following weighted-average assumptions:

	Options								ESPP
	Year ended December 31,								Year ended December 31,
	2018		2017			2016			2018			2017		2016
Expected term (years)	5.5 - 6.1			6.1			6.1			0.5			—		—
Expected volatility	82.0 - 83.2%			89.8	%		80.4	%		74.3	%		—		—
Risk-free interest rate	2.6 - 3.1%			2.0	%		1.4	%		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, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

7. Commitments & Contingencies

Contractual Obligations and Other Commitments

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 Company recognizes rent expense on a straight-line basis over the noncancelable lease period and records the difference between cash rent payments and the recognition of rent expense as deferred rent liability.

Future minimum lease payments are as follows as of December 31, 2018 (in thousands):

Year ending December 31:
2019	$	1,453
2020		1,497
2021		1,542
2022		1,588
2023		1,635
Thereafter		1,966
Total future minimum lease payments	$	9,681

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, 2018

License Agreement [Abstract]

License Agreement

8. 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., a related party, 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, as well as pay royalties in the mid to high single digits on future annual net sales, if any.

Defined Contribution Plan

12 Months Ended

Dec. 31, 2018

Compensation And Retirement Disclosure [Abstract]

Defined Contribution Plan

9. 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 $53,000 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 4% of base compensation (subject to statutory limits). During the years ended December 31, 2018, 2017 and 2016, the Company contributed $167,000, $77,000 and $62,000, respectively, to the Plan.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

No provision for income taxes was recorded for the years ended December 31, 2018, 2017 and 2016. 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 Tax Cuts and Jobs Act of 2017 (the “Tax Act”) contains tax law changes that are effective in tax years 2018 and onward. During 2018, the Company finalized its analysis of the provisional impact associated with the remeasurement of deferred tax assets. There was no change in the provisional remeasurement amount previously recorded in 2017.

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

	Year Ended December 31,
	2018			2017			2016
Domestic	$	(23,047	)	$	(7,551	)	$	(7,009	)
Foreign		(120	)		(966	)		(1,981	)
Total	$	(23,167	)	$	(8,517	)	$	(8,990	)

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 both 2016 and 2017. During the year ended December 31, 2018, the Company has utilized $175,000 of R&D tax credits as a reduction of payroll expenses to offset its payroll tax liabilities.

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

	Year Ended December 31,
	2018				2017				2016
Federal statutory income tax rate		21.0		%		34.0		%		34.0		%
State taxes, net of federal benefit		6.4				6.0				5.8
Foreign tax rate differential		0.1				(0.5	)			(0.9	)
Permanent differences		0.3				(3.8	)			(2.0	)
Research and development credit		1.4				2.5				2.6
Federal rate change impact		0.0				(31.4	)			0
Change in valuation allowance		(29.2	)			(6.8	)			(39.5	)
Provision for income taxes		—		%		—		%		—		%

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

	Year Ended December 31,
	2018			2017			2016
Deferred tax assets
Reserves and accruals	$	1,009		$	169		$	20
Net operating loss carry forwards		10,985			6,802			6,607
Research and development credit carryforwards		1,194			515			453
Gross deferred tax assets		13,188			7,486			7,080
Valuation allowance		(12,560	)		(7,434	)		(7,036	)
Net deferred tax assets		628			52			44
Deferred tax liabilities
Property and equipment		(628	)		(52	)		(44	)
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, 2018, and December 31, 2017 have been fully offset by a valuation allowance. The valuation allowance increased approximately $5.1 million, $0.4 million and $3.6 million during the years ended December 31, 2018, 2017, and 2016.

As of December 31, 2018, the Company had federal net operating loss (“NOL”) carryforward of $44.2 million and a federal research and development tax credit carryforward of $0.6 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 $22.2 million generated for year ending December 31, 2018, carryforward indefinitely. As of December 31, 2018, 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 $0.7 million, which does not expire.

As of December 31, 2018, the Company also had accumulated Australian tax losses of $1.8 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, 2018. 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. 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, the State of California 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, 2018. All years are open for examination by federal, state and Australian authorities.

Net Loss per Share

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Net Loss Per Share

11. 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,
	2018			2017			2016
Numerator:
Net loss	$	(23,167	)	$	(8,517	)	$	(8,990	)
Denominator:
Weighted-average shares of common stock outstanding		10,264,584			599,291			338,446
Net loss per share, basic and diluted	$	(2.26	)	$	(14.21	)	$	(26.56	)

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,
	2018		2017		2016
Redeemable convertible preferred stock on an if converted basis		—		12,263,126		5,966,753
Stock options to purchase common stock		2,181,466		1,213,010		680,333
Common stock subject to future vesting		89,257		238,618		485,119
Total		2,270,723		13,714,754		7,132,205

Selected Quarterly Financial Information (Unaudited)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Information (Unaudited)

12. Selected Quarterly Financial Information (Unaudited)

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

	Quarter Ended
(in thousands, except per share amount)	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	)

	Quarter Ended
(in thousands, except per share amount)	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
	(Unaudited)
Operating Expenses	$	2,257		$	1,881		$	2,192		$	2,419
Net loss	$	(2,257	)	$	(1,880	)	$	(2,080	)	$	(2,300	)
Net loss per share, basic and diluted	$	(4.43	)	$	(3.30	)	$	(3.31	)	$	(3.34	)

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.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Basis of presentation and consolidation

Basis of Presentation and Consolidation

Use of Estimates

Foreign Currency Translation

Cash and 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,
	2018		2017		2016
Cash and cash equivalents	$	24,182	$	51,033	$	9,747
Restricted cash		—		13		13
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$	24,182	$	51,046	$	9,760

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.

Fair Value of Financial Instruments

Level 1: Quoted prices in active markets for identical 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.

The following table summarizes our financial assets measured at fair value on a recurring basis (in thousands):

	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		—
Government agency bonds		17,917		—		17,917		—
Total	$	106,406	$	48,848	$	57,558	$	—

	December 31, 2017
	Total		Level 1		Level 2		Level 3
Financial Assets:
Money market funds	$	50,242	$	50,242	$	—	$	—
Total	$	50,242	$	50,242	$	—	$	—

Research and Development Costs

Research and Development Tax Incentive

Stock-Based Compensation

Income Taxes

Net Loss per Share

Accounting Pronouncements Adopted in 2018 and New Accounting Pronouncements Not Yet Adopted

Accounting Pronouncements Adopted in 2018

New Accounting Pronouncements Not Yet Adopted

Leases (Topic 842)

Other recent accounting announcements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash

	Year Ended December 31,
	2018		2017		2016
Cash and cash equivalents	$	24,182	$	51,033	$	9,747
Restricted cash		—		13		13
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$	24,182	$	51,046	$	9,760

Summary of Financial Assets and Liabilities Measured and Recognized at Fair Value on Recurring Basis

The following table summarizes our financial assets measured at fair value on a recurring basis (in thousands):

	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		—
Government agency bonds		17,917		—		17,917		—
Total	$	106,406	$	48,848	$	57,558	$	—

	December 31, 2017
	Total		Level 1		Level 2		Level 3
Financial Assets:
Money market funds	$	50,242	$	50,242	$	—	$	—
Total	$	50,242	$	50,242	$	—	$	—

	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
Government agency bonds		17,921		—		(4	)		17,917
Total	$	106,427	$	4	$	(25	)	$	106,406

	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Financial Assets:
Money market funds	$	50,242	$	—	$	—	$	50,242
Total	$	50,242	$	—	$	—	$	50,242

Cash Equivalents and Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2018

Cash And Cash Equivalents [Abstract]

Summary of Financial Assets and Liabilities Measured and Recognized at Fair Value on Recurring Basis

The following table summarizes our financial assets measured at fair value on a recurring basis (in thousands):

	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		—
Government agency bonds		17,917		—		17,917		—
Total	$	106,406	$	48,848	$	57,558	$	—

	December 31, 2017
	Total		Level 1		Level 2		Level 3
Financial Assets:
Money market funds	$	50,242	$	50,242	$	—	$	—
Total	$	50,242	$	50,242	$	—	$	—

	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
Government agency bonds		17,921		—		(4	)		17,917
Total	$	106,427	$	4	$	(25	)	$	106,406

	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Financial Assets:
Money market funds	$	50,242	$	—	$	—	$	50,242
Total	$	50,242	$	—	$	—	$	50,242

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

As of December 31, 2018, 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
Marketable securities maturing:
In one year or less	$	83,270	$	83,250
Total marketable securities	$	83,270	$	83,250

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Property and Equipment

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

	December 31, 2018			December 31, 2017
Leasehold improvements	$	3,268		$	155
Furniture, laboratory and office equipment		2,043			1,242
Computer equipment		219			34
Construction in progress		—			464
Total property and equipment		5,530			1,895
Less accumulated depreciation and amortization		(935	)		(355	)
Property and equipment, net	$	4,595		$	1,540

Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	December 31, 2018		December 31, 2017
Accrued preclinical and research costs	$	1,146	$	108
Accrued clinical costs		434		340
Accrued employee-related costs		736		422
Accrued professional services		138		—
Other		224		41
Accrued liabilities	$	2,678	$	911

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Activity under Stock Option Plan and Related Information

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

	Number of Options Outstanding			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at December 31, 2017		1,213,010		$	1.54		8.7	$	999
Options granted		1,121,901		$	5.93
Options exercised		(142,528	)	$	1.54			$	370
Options cancelled		(10,917	)	$	0.90
Outstanding at December 31, 2018		2,181,466		$	3.80		8.5	$	43,189
Vested and exercisable at December 31, 2018		833,679		$	2.00		7.7	$	18,008

Summarizes of Activity of Nonvested Restricted Stock

The following summarizes the activity of nonvested restricted stock:

	Number of Shares
Nonvested—December 31, 2017		193,394
Vested		(172,486	)
Nonvested—December 31, 2018		20,908

Stock-Based Compensation Recognized

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

	Year Ended December 31,
	2018		2017		2016
General and administrative	$	1,151	$	110	$	64
Research and development		842		93		64
Total stock-based compensation expense	$	1,993	$	203	$	128

Unrecognized Stock-based Compensation Cost and Estimated Weighted Average Amortization Period

	Unrecognized Compensation Cost		Weighted Average Remaining Amortization Period (Years)
Employee options	$	3,977		2.8
Nonemployee options		4		0.4
Total unrecognized stock-based compensation expense	$	3,981

Fair Value of Employee Stock Options Granted is Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions

The fair value of the employee stock options granted is calculated using the Black-Scholes option-pricing model with the following weighted-average assumptions:

	Options								ESPP
	Year ended December 31,								Year ended December 31,
	2018		2017			2016			2018			2017		2016
Expected term (years)	5.5 - 6.1			6.1			6.1			0.5			—		—
Expected volatility	82.0 - 83.2%			89.8	%		80.4	%		74.3	%		—		—
Risk-free interest rate	2.6 - 3.1%			2.0	%		1.4	%		2.5	%		—		—
Expected dividend yield		—		—			—			—			—		—

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Summary of Future Minimum Lease Payments

Future minimum lease payments are as follows as of December 31, 2018 (in thousands):

Year ending December 31:
2019	$	1,453
2020		1,497
2021		1,542
2022		1,588
2023		1,635
Thereafter		1,966
Total future minimum lease payments	$	9,681

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

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,
	2018			2017			2016
Domestic	$	(23,047	)	$	(7,551	)	$	(7,009	)
Foreign		(120	)		(966	)		(1,981	)
Total	$	(23,167	)	$	(8,517	)	$	(8,990	)

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,
	2018				2017				2016
Federal statutory income tax rate		21.0		%		34.0		%		34.0		%
State taxes, net of federal benefit		6.4				6.0				5.8
Foreign tax rate differential		0.1				(0.5	)			(0.9	)
Permanent differences		0.3				(3.8	)			(2.0	)
Research and development credit		1.4				2.5				2.6
Federal rate change impact		0.0				(31.4	)			0
Change in valuation allowance		(29.2	)			(6.8	)			(39.5	)
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,
	2018			2017			2016
Deferred tax assets
Reserves and accruals	$	1,009		$	169		$	20
Net operating loss carry forwards		10,985			6,802			6,607
Research and development credit carryforwards		1,194			515			453
Gross deferred tax assets		13,188			7,486			7,080
Valuation allowance		(12,560	)		(7,434	)		(7,036	)
Net deferred tax assets		628			52			44
Deferred tax liabilities
Property and equipment		(628	)		(52	)		(44	)
Net deferred tax	$	—		$	—		$	—

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2018

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,
	2018			2017			2016
Numerator:
Net loss	$	(23,167	)	$	(8,517	)	$	(8,990	)
Denominator:
Weighted-average shares of common stock outstanding		10,264,584			599,291			338,446
Net loss per share, basic and diluted	$	(2.26	)	$	(14.21	)	$	(26.56	)

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

	Year Ended December 31,
	2018		2017		2016
Redeemable convertible preferred stock on an if converted basis		—		12,263,126		5,966,753
Stock options to purchase common stock		2,181,466		1,213,010		680,333
Common stock subject to future vesting		89,257		238,618		485,119
Total		2,270,723		13,714,754		7,132,205

Selected Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

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 amount)	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	)

	Quarter Ended
(in thousands, except per share amount)	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
	(Unaudited)
Operating Expenses	$	2,257		$	1,881		$	2,192		$	2,419
Net loss	$	(2,257	)	$	(1,880	)	$	(2,080	)	$	(2,300	)
Net loss per share, basic and diluted	$	(4.43	)	$	(3.30	)	$	(3.31	)	$	(3.34	)

Organization and Description of the Business - Additional Information (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Jun. 25, 2018 USD ($) $ / shares shares	Jun. 08, 2018 $ / shares	Dec. 31, 2018 USD ($) Segment shares	Dec. 31, 2017 USD ($) 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
Common stock, shares authorized			125,000,000	96,000,000
Preferred stock, shares authorized			10,000,000	0
Accumulated deficit \| $			$ 49,195	$ 26,028
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

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents	$ 24,182	$ 51,033	$ 9,747
Restricted cash		13	13
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$ 24,182	$ 51,046	$ 9,760	$ 19,766

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary Of Significant Accounting Policies [Line Items]
Impairment losses	$ 0
Transfers from Level 1 to Level 2	0
Transfers from Level 2 to Level 1	0
Reduction of research and development expenses	5,000	$ 499,000	$ 385,000
Research and development tax credit receivable	5,000	$ 498,000
Interest charges or penalties related to unrecognized tax benefits	0
Operating leases liability expected to recognize	7,100,000
Operating lease right of use asset	4,200,000
Deferred rent	$ 2,900,000
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	$ 1,000,000

Summary of Significant Accounting Policies - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 83,250
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	106,406	$ 50,242
Fair Value, Measurements, Recurring \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	48,848	50,242
Fair Value, Measurements, Recurring \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	57,558
Fair Value, Measurements, Recurring \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	23,156	50,242
Fair Value, Measurements, Recurring \| Money Market Funds \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	23,156	$ 50,242
Fair Value, Measurements, Recurring \| U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	25,692
Fair Value, Measurements, Recurring \| U.S. Treasury Securities \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	25,692
Fair Value, Measurements, Recurring \| Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	19,190
Fair Value, Measurements, Recurring \| Commercial paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	19,190
Fair Value, Measurements, Recurring \| Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	20,451
Fair Value, Measurements, Recurring \| Corporate Debt Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	20,451
Fair Value, Measurements, Recurring \| Government agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	17,917
Fair Value, Measurements, Recurring \| Government agency bonds \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial Assets	$ 17,917

Cash Equivalents and Marketable Securities - Summary of Financial Assets and Liabilities Measured and Recognized at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 83,270
Fair Value	83,250
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	106,427	$ 50,242
Unrealized Gains	4
Unrealized Losses	(25)
Fair Value	106,406	50,242
Fair Value, Measurements, Recurring \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	23,156	50,242
Fair Value	23,156	$ 50,242
Fair Value, Measurements, Recurring \| U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	25,698
Unrealized Losses	(6)
Fair Value	25,692
Fair Value, Measurements, Recurring \| Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	19,203
Unrealized Losses	(13)
Fair Value	19,190
Fair Value, Measurements, Recurring \| Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	20,449
Unrealized Gains	4
Unrealized Losses	(2)
Fair Value	20,451
Fair Value, Measurements, Recurring \| Government agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	17,921
Unrealized Losses	(4)
Fair Value	$ 17,917

Cash Equivalents and Marketable Securities - Summary of Amortized Cost and Estimated Fair Value of Available-for-sale Securities by Contractual Maturity (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Marketable securities maturing, Amortized Cost:
In one year or less, Amortized Cost	$ 83,270
Total marketable securities, Amortized Cost	83,270
Marketable securities maturing, Estimated Fair Value:
In one year or less, Estimated Fair Value	83,250
Total marketable securities, Estimated Fair Value	$ 83,250

Cash Equivalents and Marketable Securities - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)
Cash And Cash Equivalents [Abstract]
Sale of available-for-sale securities	$ 0

Balance Sheet Components - Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Total property and equipment	$ 5,530	$ 1,895
Less accumulated depreciation and amortization	(935)	(355)
Property and equipment, net	4,595	1,540
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	3,268	155
Furniture, Laboratory and Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	2,043	1,242
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 219	34
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment		$ 464

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Depreciation Expense	$ 690	$ 175	$ 154
Leasehold Improvements
Property Plant And Equipment [Line Items]
Incentive received from landlord to construct leasehold improvements	$ 3,200

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accrued preclinical and research costs	$ 1,146	$ 108
Accrued clinical costs	434	340
Accrued employee-related costs	736	422
Accrued professional services	138
Other	224	41
Accrued liabilities	$ 2,678	$ 911

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, 2018 USD ($) ExecutiveOfficer $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted		1,121,901
Maximum number of shares issued upon exercise of incentive stock options		833,679
Total intrinsic value of exercised stock options \| $		$ 370,000
Stock-based compensation expense recognized \| $		1,993,000	$ 203,000	$ 128,000
Payments of dividends of common stock \| $		$ 0
Expected dividend yield		0.00%
Early Exercise Stock Purchase Agreements
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		36 months
Nonvested common shares outstanding		68,349	45,224
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 Purchase Agreements
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued upon early exercise of stock options are subject to repurchase \| $		$ 112,000	$ 18,000
Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term			6 years 1 month 6 days	6 years 1 month 6 days
Employee options \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term		6 years 1 month 6 days
Employee options \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term		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		115,657	0
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	193,394
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term		6 months
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future issuance		1,802,145
Number of shares will increase automatically through every year on specified date		--01-01
Number of shares increase automatically continuing through maximum period		January 1 of each year, 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 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 \| Common Stock \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares available for issuance		4,000,000
2018 Equity Incentive Plan \| Employee options \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted		85,621
2018 Equity Incentive Plan \| Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of RSU granted		10,189	0
Weighted-average estimated grant-date fair value \| $ / shares		$ 17.75
Stock-based compensation expense recognized \| $		$ 181,000
2018 Equity Incentive Plan \| Incentive Stock Options \| Common Stock \| Maximum [Member]
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
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		2,095,845
Weighted average grant date fair value of options granted \| $ / shares		$ 4.23	$ 1.61
Total intrinsic value of exercised stock options \| $		$ 370,000	$ 0
2015 Equity Incentive Plan \| Maximum [Member]
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		200,000
Common stock issued		0
Authorized an offering beginning period		Nov. 16, 2018
Authorized an offering ending period		May 15, 2019
2018 Employee Stock Purchase Plan \| Common Stock \| Maximum [Member]
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 Plan and Related Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of options outstanding, Outstanding, Beginning balance	1,213,010
Number of options outstanding, Options granted	1,121,901
Number of options outstanding, Options exercised	(142,528)
Number of options outstanding, Options cancelled	(10,917)
Number of options outstanding, Outstanding, Ending balance	2,181,466	1,213,010
Number of options outstanding, options vested and exercisable	833,679
Weighted average exercise price, Outstanding, Beginning balance	$ 1.54
Weighted average exercise price, Options granted	5.93
Weighted average exercise price, Options exercised	1.54
Weighted average exercise price, Options cancelled	0.90
Weighted average exercise price, Outstanding, Ending balance	3.80	$ 1.54
Weighted average exercise price, options vested and exercisable	$ 2.00
Weighted average remaining contractual term, Outstanding, Beginning balance	8 years 6 months	8 years 8 months 12 days
Weighted average remaining contractual term,options vested and exercisable	7 years 8 months 12 days
Aggregate intrinsic value, Outstanding, Beginning balance	$ 999
Aggregate intrinsic value, Options exercised	370
Aggregate intrinsic value, Outstanding, Ending balance	43,189	$ 999
Aggregate intrinsic value, options vested and exercisable	$ 18,008

Stock-Based Compensation - Summarizes of Activity of Nonvested Restricted Stock (Details) - Restricted Stock	12 Months Ended
	Dec. 31, 2018 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested beginning balance	193,394
Number of Shares Outstanding, Vested	(172,486)
Nonvested ending balance	20,908

Stock-Based Compensation - Stock-Based Compensation Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,993	$ 203	$ 128
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,151	110	64
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 842	$ 93	$ 64

Stock-Based Compensation - Unrecognized Stock-based Compensation Cost and Estimated Weighted Average Amortization Period (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Unrecognized compensation cost	$ 3,981
Employee options
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Unrecognized compensation cost	$ 3,977
Weighted average remaining amortization period (years)	2 years 9 months 18 days
Nonemployee options
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Unrecognized costs of unvested options awarded	$ 4
Weighted average remaining amortization period (years)	4 months 24 days

Stock-Based Compensation - Fair Value of Employee Stock Options Granted is Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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	6 years 1 month 6 days
Expected volatility		89.80%	80.40%
Expected volatility, Minimum	82.00%
Expected volatility, Maximum	83.20%
Risk-free interest rate		2.00%	1.40%
Risk-free interest rate, Minimum	2.60%
Risk-free interest rate, Maximum	3.10%
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	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 6 months
Maximum [Member] \| Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 1 month 6 days

Commitments and Contingencies - Additional Information (Details)	1 Months Ended
	Aug. 31, 2017 ft²
Commitments And Contingencies Disclosure [Abstract]
Operating lease area	24,357
Lease commenced date	Mar. 01, 2018
Lease termination date	Feb. 28, 2025

Commitments and Contingencies - Summary of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 1,453
2020	1,497
2021	1,542
2022	1,588
2023	1,635
Thereafter	1,966
Total future minimum lease payments	$ 9,681

License Agreement - Additional Information (Details)	1 Months Ended
License Agreement - Additional Information (Details)	Jun. 30, 2015 USD ($)
License Agreement \| Amgen, Inc [Member]
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Employees contributions amount up to lesser of pre-tax compensation	$ 53,000
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	$ 167,000	$ 77,000	$ 62,000
Maximum [Member]
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes Disclosure [Line Items]
Provision for income taxes		$ 0	$ 0	$ 0
Provisional remeasurement amount of deferred tax assets			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		175,000
Valuation allowance increased		$ 5,100,000	$ 400,000	$ 3,600,000
Period for change in ownership percentage for net operating loss carryforwards		3 years
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
Minimum
Income Taxes Disclosure [Line Items]
Percentage of change in ownership for net operating loss carryforwards		50.00%
Australian Taxation Office
Income Taxes Disclosure [Line Items]
Net operating loss (NOL) carryforwards		$ 1,800,000
Federal
Income Taxes Disclosure [Line Items]
Net operating loss (NOL) carryforwards		$ 44,200,000
Net operating loss carryforwards expiration start year		2035
Net operating loss (NOL) carryforwards indefinite		$ 22,200,000
Federal \| Research and Development
Income Taxes Disclosure [Line Items]
Tax credit carryforward expiration start year		2035
Tax credit carryforward		$ 600,000
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		$ 700,000

Income Taxes - Schedule of Domestic and Foreign Components of Net Loss (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Total	$ (5,782)	$ (5,663)	$ (6,775)	$ (4,947)	$ (2,300)	$ (2,080)	$ (1,880)	$ (2,257)	$ (23,167)	$ (8,517)	$ (8,990)
Domestic
Operating Loss Carryforwards [Line Items]
Total									(23,047)	(7,551)	(7,009)
Foreign
Operating Loss Carryforwards [Line Items]
Total									$ (120)	$ (966)	$ (1,981)

- 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Federal statutory income tax rate	21.00%	34.00%	34.00%
State taxes, net of federal benefit	6.40%	6.00%	5.80%
Foreign tax rate differential	0.10%	(0.50%)	(0.90%)
Permanent differences	0.30%	(3.80%)	(2.00%)
Research and development credit	1.40%	2.50%	2.60%
Federal rate change impact	0.00%	(31.40%)	0.00%
Change in valuation allowance	(29.20%)	(6.80%)	(39.50%)

Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Reserves and accruals	$ 1,009	$ 169	$ 20
Net operating loss carry forwards	10,985	6,802	6,607
Research and development credit carryforwards	1,194	515	453
Gross deferred tax assets	13,188	7,486	7,080
Valuation allowance	(12,560)	(7,434)	(7,036)
Net deferred tax assets	628	52	44
Deferred tax liabilities
Property and equipment	$ (628)	$ (52)	$ (44)

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net loss	$ (5,782)	$ (5,663)	$ (6,775)	$ (4,947)	$ (2,300)	$ (2,080)	$ (1,880)	$ (2,257)	$ (23,167)	$ (8,517)	$ (8,990)
Denominator:
Weighted-average shares of common stock outstanding									10,264,584	599,291	338,446
Net loss per common share, basic and diluted	$ (0.30)	$ (0.30)	$ (3.31)	$ (6.53)	$ (3.34)	$ (3.31)	$ (3.30)	$ (4.43)	$ (2.26)	$ (14.21)	$ (26.56)

- 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	2,270,723	13,714,754	7,132,205
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	5,966,753
Stock 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	2,181,466	1,213,010	680,333
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	89,257	238,618	485,119

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Operating Expenses	$ 6,426	$ 6,264	$ 6,950	$ 5,086	$ 2,419	$ 2,192	$ 1,881	$ 2,257	$ 24,726	$ 8,749	$ 8,990
Net loss	$ (5,782)	$ (5,663)	$ (6,775)	$ (4,947)	$ (2,300)	$ (2,080)	$ (1,880)	$ (2,257)	$ (23,167)	$ (8,517)	$ (8,990)
Net loss per common share, basic and diluted	$ (0.30)	$ (0.30)	$ (3.31)	$ (6.53)	$ (3.34)	$ (3.31)	$ (3.30)	$ (4.43)	$ (2.26)	$ (14.21)	$ (26.56)

- Definition

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

+ References + Details