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Document And Entity Information - USD ($)	12 Months Ended
Document And Entity Information - USD ($)	Dec. 31, 2019	Mar. 16, 2020
Document And Entity Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	IGM Biosciences, Inc.
Entity Central Index Key	0001496323
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Public Float	$ 264,500,000
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	IGMS
Security Exchange Name	NASDAQ
Entity File Number	001-39045
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	77-0349194
Entity Address, Address Line One	325 E. Middlefield Road
Entity Address, City or Town	Mountain View
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94043
City Area Code	650
Local Phone Number	965-7873
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	Certain sections of the Registrant’s definitive Proxy Statement to be filed in connection with the Registrant’s 2020 Annual Meeting of Stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such definitive Proxy Statement will be filed with the Securities and Exchange Commission pursuant to Regulation 14A within 120 of the Registrant’s fiscal year ended December 31, 2019.
Common Stock
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		24,128,065
Non-voting Common Stock
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		6,431,205

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 35,891	$ 1,887
Short-term investments	188,743
Prepaid expenses and other current assets	6,431	485
Income tax receivable	35	35
Total current assets	231,100	2,407
Property and equipment, net	3,882	1,472
Long-term investments	11,973
Operating lease right-of-use asset	14,137
Restricted cash		100
Other assets	258
Total assets	261,350	3,979
Current liabilities:
Accounts payable	3,087	164
Accrued liabilities	3,305	3,582
Lease liabilities, current	2,483
Deferred rent		108
Related party loan		5,027
Other current liabilities		9
Total current liabilities	8,875	8,890
Lease liabilities, non-current	12,244
Total liabilities	21,119	8,890
Commitments and contingencies (Note 10)
Convertible preferred stock, $0.01 par value; 0 shares authorized as of December 31, 2019 and 9,501,624 shares authorized as of December 31, 2018; 0 shares issued and outstanding as of December 31, 2019 and 9,501,620 issued and outstanding as of December 31, 2018; liquidation value of $0 as of December 31, 2019 and $61,466 as of December 31, 2018		60,917
Stockholders' equity (deficit);
Preferred stock, $0.01 par value; 200,000,000 shares authorized as of December 31, 2019 and 0 shares authorized as of December 31, 2018; 0 shares issued and outstanding as of December 31, 2019 and December 31, 2018
Common stock, value	240	4
Additional paid-in-capital	347,089	751
Due from related party		(2,511)
Accumulated other comprehensive income	43
Accumulated deficit	(107,205)	(64,072)
Total stockholders’ equity (deficit)	240,231	(65,828)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	261,350	$ 3,979
Non-voting Common Stock
Stockholders' equity (deficit);
Common stock, value	64
Total stockholders’ equity (deficit)	$ 64

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Convertible preferred stock, par value	$ 0.01	$ 0.01
Convertible preferred stock, shares authorized	0	9,501,624
Convertible preferred stock, shares issued	0	9,501,620
Convertible preferred stock, shares outstanding	0	9,501,620
Convertible preferred stock, liquidation preference, value	$ 0	$ 61,466
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	200,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,000,000,000	30,264,511
Common stock, shares issued	24,053,921	438,074
Common stock, shares outstanding	24,053,921	438,074
Non-voting Common Stock
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	6,431,208	0
Common stock, shares issued	6,431,205	0
Common stock, shares outstanding	6,431,205	0

Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	Due To (From) Related Party	Convertible Preferred Stock	Non-voting Common Stock	Series C Convertible Preferred Stock	Common Stock	Common Stock IPO	Additional Paid-In Capital	Additional Paid-In Capital IPO	Accumulated Other Comprehensive Income	Accumulated Deficit
Convertible preferred stock balance at Dec. 31, 2016				$ 33,004
Convertible preferred stock balance, shares at Dec. 31, 2016				5,238,771
Issuance of Series B & C convertible preferred stock, net of issuance costs				$ 8,000
Issuance of Series B & C convertible preferred stock, net of issuance costs, shares				1,210,580
Shares repurchased and retired				$ (221)
Shares repurchased and retired, shares				(64,554)
Convertible preferred stock balance at Dec. 31, 2017				$ 40,783
Convertible preferred stock balance, shares at Dec. 31, 2017				6,384,797
Balance at Dec. 31, 2016	$ (29,703)						$ 4		$ 600			$ (30,307)
Balance, shares at Dec. 31, 2016							434,859
Exercise of stock options	3								3
Exercise of stock options, shares							3,215
Shares repurchased and retired	221								221
Related party equity transaction			$ (34,625)						34,625
Tax resulting from related party transactions	(128)								(128)
Capital contribution from related party	65								65
Stock-based compensation expense	93								93
Net loss	(11,054)											(11,054)
Balance at Dec. 31, 2017	(40,503)		(34,625)				$ 4		35,479			(41,361)
Balance, shares at Dec. 31, 2017							438,074
Issuance of Series B & C convertible preferred stock, net of issuance costs				$ 20,134
Issuance of Series B & C convertible preferred stock, net of issuance costs, shares				3,116,823
Convertible preferred stock balance at Dec. 31, 2018	$ 60,917			$ 60,917
Convertible preferred stock balance, shares at Dec. 31, 2018	9,501,620			9,501,620
Issuance of common stock	$ (2,797)		(2,511)						(286)
Related party equity transaction			34,625						(34,625)
Stock-based compensation expense	183								183
Net loss	(22,711)											(22,711)
Balance at Dec. 31, 2018	$ (65,828)		(2,511)				$ 4		751			(64,072)
Balance, shares at Dec. 31, 2018							438,074
Issuance of Series B & C convertible preferred stock, net of issuance costs				$ 101,636
Issuance of Series B & C convertible preferred stock, net of issuance costs, shares				7,717,446		7,717,446
Conversion of convertible preferred stock into common stock and non-voting common stock				$ (162,553)
Conversion of convertible preferred stock into common stock and non-voting common stock, shares				(17,219,066)
Convertible preferred stock balance, shares at Dec. 31, 2019	0			0
Issuance of common stock	$ 11	$ 182,842						$ 125	11	$ 182,717
Issuance of common stock, shares							7,566	12,578,125
Exercise of stock options	$ 179						$ 2		177
Exercise of stock options, shares	184,036						184,036
Vesting of restricted stock							$ 1		(1)
Vesting of restricted stock							58,259
Conversion of convertible preferred stock into common stock and non-voting common stock	$ 162,553				$ 64		$ 108		162,381
Conversion of convertible preferred stock into common stock and non-voting common stock, shares					6,431,205		10,787,861
Unrealized gain on investments	43										$ 43
Related party equity transaction	2,550		$ 2,511						39
Stock-based compensation expense	1,014								1,014
Net loss	(43,133)											(43,133)
Balance at Dec. 31, 2019	$ 240,231				$ 64		$ 240		$ 347,089		$ 43	$ (107,205)
Balance, shares at Dec. 31, 2019					6,431,205		24,053,921

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (43,133)	$ (22,711)	$ (11,054)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	597	278	161
Stock-based compensation expense	1,014	183	93
Accrued interest on related party loan		27
Net amortization of premiums and accretion of discounts on investments	(306)
Non-cash lease expense	1,736
Changes in assets and liabilities:
Prepaid expenses and other current assets	(5,412)	(262)	(54)
Other assets	(258)	8	(8)
Income tax receivable		(35)
Accounts payable	1,961	(61)	128
Accrued liabilities	(25)	2,791	316
Income tax payable		(128)
Deferred rent		(134)	52
Lease liabilities	(1,254)
Other current liabilities	(9)	9
Other long-term liabilities	(27)	(9)	9
Net cash used in operating activities	(45,116)	(20,044)	(10,357)
Cash flows from investing activities:
Purchase of property and equipment	(2,337)	(788)	(385)
Purchases of investments	(208,901)
Maturities of investments	8,000
Net cash used in investing activities	(203,238)	(788)	(385)
Cash flows from financing activities:
Proceeds from common stock issuance	11
Proceeds from exercise of stock options	179		3
Proceeds from issuance of initial public offering, net of underwriters' commission	187,162
Net cash provided by financing activities	282,258	22,337	8,068
Net increase (decrease) in cash, cash equivalents and restricted cash	33,904	1,505	(2,674)
Cash, cash equivalents, and restricted cash, beginning of year	1,987	482	3,156
Cash, cash equivalents, and restricted cash, end of year	35,891	1,987	482
Cash and cash equivalents	35,891	1,887	432
Restricted cash		100	50
Supplemental disclosure of cash flow information:
Cash paid for income taxes		167
Supplemental disclosure of non-cash investing and financing activities:
Acquisition of property and equipment in accounts payable and accrued liabilities	962	292	8
Conversion of convertible preferred stock into common stock and non-voting common stock	162,553
IPO
Cash flows from financing activities:
Payment of issuance costs	(4,320)
Series B Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock		20,100
Series C Convertible Preferred Stock
Cash flows from financing activities:
Payment of issuance costs	(324)
Supplemental disclosure of non-cash investing and financing activities:
Issuance costs in accounts payable and accrued liabilities	40
New Investors \| Series B Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock		17,337	8,000
New Investors \| Series C Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock	72,000
Haldor Topsøe Holding A/S and Holdco
Cash flows from financing activities:
Proceeds from related party capital contribution	2,550		65
Proceeds from loan from related party	15,000	5,000
Supplemental disclosure of cash flow information:
Cash paid for interest on related party loan	297
Supplemental disclosure of non-cash investing and financing activities:
Settlement of related party loan through issuance of Series C convertible preferred stock	20,000
Stock repurchase paid by related party			221
Related party equity transaction		34,625	$ (34,625)
Haldor Topsøe Holding A/S and Holdco \| Series B Convertible Preferred Stock
Supplemental disclosure of non-cash investing and financing activities:
Receivable from related party for Series B convertible preferred stock		$ 2,511
Haldor Topsøe Holding A/S and Holdco \| Series C Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock	$ 10,000

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Note 2. Summary of Significant Accounting Policies

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company evaluates its estimates, including, but not limited to, those related to investments, manufacturing accruals, accrued research and development expenses, fair value of common stock, stock-based compensation, operating lease right-of-use (ROU) assets and liabilities, income tax uncertainties and the valuation of deferred tax assets. The Company bases its estimates on its historical experience and also on assumptions that it believes are reasonable; however, actual results could significantly differ from those estimates.

Segments

The Company operates and manages its business as one reportable and operating segment, which is the business of developing engineered IgM antibodies for the treatment of cancer. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for allocating and evaluating financial performance. All long-lived assets are maintained in, and all losses are attributable to, the United States of America.

Concentration of Credit Risk and Other Risks and Uncertainties

Financial instruments that potentially subject the Company to a concentration of credit risk consist primarily of cash and investments. The Company invests in money market funds, U.S. Treasury securities, U.S. government agency securities, corporate debt and commercial paper. The Company maintains bank deposits in federally insured financial institutions and these deposits may exceed federally insured limits. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash and cash equivalents and issuers of investments to the extent recorded on the balance sheets. The Company’s investment policy limits investments to money market funds, certain types of debt securities issued by the U.S. Government and its agencies, corporate debt, commercial paper, and places restrictions on the credit ratings, maturities and concentration by type and issuer. The Company has not experienced any losses on its deposits of cash and investments.

The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, the Company’s early stages of clinical drug development; uncertainties related to the use of engineered IgM antibodies, which is a novel and unproven therapeutic approach; the Company’s ability to advance product candidates into, and successfully complete, clinical trials on the timelines it projects; the Company’s ability to adequately demonstrate sufficient safety and efficacy of its product candidates; the Company’s ability to enroll patients in its ongoing and future clinical trials; the Company’s ability to successfully manufacture and supply its product candidates for clinical trials; the Company’s ability to obtain additional capital to finance its operations; uncertainties related to the projections of the size of patient populations suffering from the diseases the Company is targeting; the Company’s ability to obtain, maintain, and protect its intellectual property rights; developments relating to the Company’s competitors and its industry, including competing product candidates and therapies; general economic and market conditions; and other risks and uncertainties.

The Company’s product candidates will require approvals from the U.S. Food and Drug Administration and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.

Cash, Cash Equivalents and Restricted Cash

The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash and cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts and are stated at fair value. Restricted cash consisted of a money market account that served as collateral for a credit card agreement at one of the Company’s financial institutions.

Investments

The Company’s investments have been classified and accounted for as available-for-sale securities. Fixed income securities consist of U.S. Treasury securities, U.S. government agency securities, corporate debt, and commercial paper. The specific identification method is used to determine the cost basis of fixed income securities sold. These securities are recorded on the balance sheets at fair value. Unrealized gains and losses on these securities are included as a separate component of accumulated other comprehensive income. The cost of investment securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion are included in other income, net. Realized gains and losses and declines in fair value judged to be other-than-temporary, if any, are also included in other income, net. The Company evaluates securities for other-than-temporary impairment at the balance sheet date. Declines in fair value determined to be other-than-temporary are also included in other income, net. The Company classifies its investments as short or long term primarily based on the remaining contractual maturity of the securities.

Property and Equipment

Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is determined using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or the estimated useful economic lives of the related assets.

Upon retirement or sale of the assets, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss are recorded to the statements of operations. Repairs and maintenance are charged to operations as incurred.

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment. The Company evaluates the carrying amount of its long-lived assets whenever events or changes in circumstances indicate that the assets may not be recoverable. An impairment loss would be recognized when estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount of the asset. There was no impairment of long-lived assets in 2019, 2018 and 2017.

Convertible Preferred Stock

The Company records shares of convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs. The convertible preferred stock is recorded outside of stockholders’ deficit on the balance sheets because the shares contain liquidation features that are not solely within the Company’s control. The Company has elected not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because of the uncertainty of whether or when such an event would occur. Subsequent adjustments to increase the carrying values to the liquidation preferences will be made only when it becomes probable that such a liquidation event will occur.

Research and Development Expenses

The Company expenses research and developments costs as they are incurred. Research and development expenses consist primarily of: (i) personnel-related expenses, including salaries, benefits and stock-based compensation expense, for personnel in the Company’s research and development functions; (ii) fees paid to third parties such as contractors, consultants and contract research organizations (CROs), for animal studies and other costs related to preclinical and clinical testing; (iii) costs related to acquiring and manufacturing research and clinical trial materials, including under agreements with third parties such as contract manufacturing organizations (CMOs), and other vendors; (iv) costs related to the preparation of regulatory submissions; (v) expenses related to laboratory supplies and services; and (vi) depreciation of equipment and facilities expenses.

Accrued Research and Development Expenses

The Company records accruals for estimated costs of research, preclinical studies, clinical trials, and manufacturing, which are significant components of research and development expenses. A substantial portion of the Company’s ongoing research and development activities is conducted by third-party service providers, CROs and CMOs. The Company’s contracts with the CMOs generally include fees such as initiation fees, reservation fees, costs related to animal studies and safety tests, verification run costs, materials and reagents expenses, taxes, etc. The Company’s contracts with CROs generally include pass-through fees such as regulatory expenses, investigator fees, travel costs and other miscellaneous costs, including shipping and printing fees. The financial terms of these contracts are subject to negotiations, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company accrues the costs incurred under agreements with these third parties based on estimates of actual work completed in accordance with the respective agreements. The Company determines the estimated costs through discussions with internal personnel and external service providers as to the progress, or stage of completion or actual timeline (start-date and end-date) of the services and the agreed-upon fees to be paid for such services. In the event the Company makes advance payments, the payments are recorded as a prepaid expense and recognized as the services are performed.

As actual costs become known, the Company adjusts its accruals. Although the Company does not expect its estimates to be materially different from amounts actually incurred, such estimates for the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in us reporting amounts that are too high or too low in any particular period. The Company’s accrual is dependent, in part, upon the receipt of timely and accurate reporting from CROs and other third-party vendors. Variations in the assumptions used to estimate accruals including, but not limited to, the number of patients enrolled, the rate of patient enrollment and the actual services performed, may vary from the Company’s estimates, resulting in adjustments to clinical trial expenses in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect its financial condition and results of operations. Through December 31, 2019, there have been no material differences from the Company’s estimated accrued research and development expenses to actual expenses.

Stock-Based Compensation

The Company accounts for stock-based compensation by measuring and recognizing compensation expense for all share-based awards made to employees, non-employees and directors based on estimated grant-date fair values. The Company uses the straight-line method to allocate compensation cost to reporting periods over the requisite service period, which is generally the vesting period, and estimates the fair value of share-based awards to employees and directors using the Black-Scholes option-pricing model. The Company accounts for forfeitures as they occur. The fair value of each purchase under the employee stock purchase plan (ESPP) is estimated at the beginning of the offering period using the Black-Scholes option pricing model and recorded as expense over the service period using the straight-line method.

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 (including non-voting common stock) outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.

Deferred Offering Costs

Deferred offering costs, consisting of legal, accounting, and filing fees directly relating to the IPO, were capitalized and offset against the IPO proceeds upon the completion of the offering. For the year ended December 31, 2018, there were no offering costs incurred. Upon completion of the IPO, approximately $4.3 million of deferred offering costs were offset against the IPO proceeds in additional paid-in capital.

Leases

During 2019, the Company elected to early adopt Accounting Standard Update (ASU) No. 2016-02, Leases (ASC 842) and its associated amendments as of January 1, 2019 using the modified retrospective transition approach. There was no cumulative-effect adjustment recorded to accumulated deficit upon adoption.

Under ASC 842, the Company determines if an arrangement is a lease at inception. In addition, the Company determines whether leases meet the classification criteria of a finance or operating lease at the lease commencement date considering: (1) whether the lease transfers ownership of the underlying asset to the lessee at the end of the lease term, (2) whether the lease grants the lessee an option to purchase the underlying asset that the lessee is reasonably certain to exercise, (3) whether the lease term is for a major part of the remaining economic life of the underlying asset, (4) whether the present value of the sum of the lease payments and residual value guaranteed by the lessee equals or exceeds substantially all of the fair value of the underlying asset, and (5) whether the underlying asset is of such a specialized nature that it is expected to have no alternative use to the lessor at the end of the lease term. As of December 31, 2019, the Company's lease population consisted of real estate. As of the date of adoption of ASC 842 and December 31, 2019, the Company did not have finance leases.

Operating leases are included in operating lease right-of-use (ROU) assets, lease liabilities, current, and lease liabilities, non-current in the Company’s balance sheet. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date if the rate implicit in the lease is not readily determinable. The Company determines the incremental borrowing rate base on an analysis of corporate bond yields with a credit rating similar to the Company. The determination of the Company’s incremental borrowing rate requires management judgment including the development of a synthetic credit rating and cost of debt as the Company currently does not carry any debt. The Company believes that the estimates used in determining the incremental borrowing rate are reasonable based upon current facts and circumstances. Applying different judgments to the same facts and circumstances could result in the estimated amounts to vary. The operating lease ROU assets also include adjustments for prepayments and accrued lease payments and exclude lease incentives. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise such options. Operating lease cost is recognized on a straight-line basis over the expected lease term. Lease agreements entered into after the adoption of ASC 842 that include lease and non-lease components are accounted for as a single lease component. Lease agreements with a noncancelable term of less than 12 months are not recorded on the Company’s balance sheet. For more information about the impact of adoption and disclosures on the Company’s leases, refer to “Note 10 – Commitments and Contingencies.”

Income Taxes

The Company accounts for income taxes using the liability method, whereby deferred tax asset and liability account balances are determined based on differences between the financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company provides a valuation allowance when it is more likely than not that some portion, or all of the Company’s deferred tax assets will not be realized.

The Company accounts for income tax contingencies using a benefit recognition model. If it considers that a tax position is more likely than not to be sustained upon audit, based solely on the technical merits of the position, it recognizes the benefit. The Company measures the benefit by determining the amount that is greater than 50% likely of being realized upon settlement, presuming that the tax position is examined by the appropriate taxing authority that has full knowledge of all relevant information. 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 or penalties charged in relation to the unrecognized tax benefits.

Recently Adopted Accounting Standards

During 2019, the Company elected to early adopt ASC 842 and its associated amendments as of January 1, 2019 using the modified retrospective transition approach by applying the new standard to all leases existing at the date of initial application and not restating comparative periods. There was no cumulative-effect adjustment recorded to accumulated deficit upon adoption. Under ASC 842, a lessee is required to recognize a lease liability and ROU asset for all leases. The new guidance also modified the classification criteria and requires additional disclosures to enable users of financial statements to understand the amount, timing, and uncertainty of cash flows arising from leases. Consistent with current guidance, a lessee’s recognition, measurement, and presentation of expenses and cash flows arising from a lease continue to depend primarily on its classification. The Company elected the package of three practical expedients permitted under the transition guidance, which allowed the Company to carryforward its historical lease classification, its assessment on whether a contract was or contains a lease, and its initial direct costs for any leases that existed prior to January 1, 2019. In addition, the Company elected the following transitional practical expedients: (1) the short-term lease exception and (2) to not separate its non-lease components for its real estate leases. The impact of adoption and additional disclosures required by the ASU have been included in “Significant Accounting Policies - Leases” above and in “Note 10 – Commitments and Contingencies.”

In June 2018, the FASB issued ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting. This ASU simplifies the accounting for share-based awards to nonemployees by aligning it with the accounting for share-based awards to employees, with certain exceptions. This ASU is effective for annual periods beginning after December 15, 2019, and interim periods within annual periods beginning after December 15, 2020. Early adoption is permitted. The Company adopted this ASU as of January 1, 2019 and the adoption did not have a material impact on its financial statements and related disclosures.

Recently Issued Accounting Pronouncements

In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. This ASU also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. This ASU is effective for fiscal years beginning after December 15, 2022 and interim periods within those fiscal years. Early adoption is permitted. The Company is currently assessing the impact of this standard on its financial statements and related disclosures.

In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, which amends ASC 820, Fair Value Measurement. This ASU modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. The effective date is the first quarter of fiscal year 2020, with early adoption permitted for the removed disclosures and delayed adoption until fiscal year 2020 permitted for the new disclosures. The removed and modified disclosures will be adopted on a retrospective basis and the new disclosures will be adopted on a prospective basis. The Company is currently assessing the impact of this standard on its financial statements and related disclosures.

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard will be effective beginning January 1, 2021. The Company is currently assessing the impact of this standard on its financial statements and related disclosures.

Fair Value Measurement

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurement

Note 3. Fair Value Measurement

The Company applies fair value accounting for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a three-tier fair value hierarchy has been established, which prioritizes the inputs used in measuring fair value as follows:

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

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 which reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model.

In determining fair value, the Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible as well as considers counterparty credit risk in its assessment of fair value.

Financial instruments classified within Level 2 of the fair value hierarchy are valued based on other observable inputs, including broker or dealer quotations or alternative pricing sources. When quoted prices in active markets for identical assets or liabilities are not available, the Company relies on non-binding quotes from its investment managers, which are based on proprietary valuation models of independent pricing services. These models generally use inputs such as observable market data, quoted market prices for similar instruments, or historical pricing trends of a security relative to its peers. To validate the fair value determination provided by its investment managers, the Company reviews the pricing movement in the context of overall market trends and trading information from its investment managers. In addition, the Company assesses the inputs and methods used in determining the fair value in order to determine the classification of securities in the fair value hierarchy.

As of December 31, 2019, investments measured and recognized at fair value are as follows (in thousands):

		December 31, 2019
	Fair Value Hierarchy Level	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Investments
U.S. Treasury securities	Level 1	$	66,244	$	48	$	—		$	66,292
Corporate bonds	Level 2		39,953		3		—			39,956
Commercial paper	Level 2		74,507		—		(9	)		74,498
U.S. government agency securities	Level 2		19,969		1		—			19,970
Total		$	200,673	$	52	$	(9	)	$	200,716

As of December 31, 2018, there were no investments measured and recognized at fair value.

The following table presents the contractual maturities of the Company’s investments as of December 31, 2019 (in thousands):

	December 31, 2019
Due in less than one year	$	188,743
Due in more than one year		11,973
Total	$	200,716

- Definition

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

+ References + Details

Convertible Preferred Stock

12 Months Ended

Dec. 31, 2019

Temporary Equity Disclosure [Abstract]

Convertible Preferred Stock

Note 7. Convertible Preferred Stock

Issued and outstanding convertible preferred stock and its principal terms as of December 31, 2018 were as follows (in thousands, except share and per share amounts):

	Authorized Shares		Shares Issued and Outstanding		Original Issue Price		Carrying Value		Aggregate Liquidation Preference
Series A convertible preferred stock		401,004		401,004	$	3.3042	$	1,325	$	1,325
Series B convertible preferred stock		9,100,620		9,100,616	$	6.6084		59,592		60,141
Total		9,501,624		9,501,620			$	60,917	$	61,466

During 2018, the Company issued 3,116,823 shares of Series B convertible preferred stock for proceeds of $20.1 million, net of issuance costs.

In October 2018, the Company exchanged its existing common shares into 438,074 shares of common stock, 401,004 shares of Series A convertible preferred stock and 9,100,616 shares of Series B convertible preferred stock. All of the share information referenced throughout the financial statements and notes to the financial statements have been retroactively adjusted to reflect the change in capital structure. As a result of this change in capital structure, there was no additional stock-based compensation expense recorded.

As of December 31, 2018, the holders of the convertible preferred stock had the following rights and preferences:

Voting rights

Each share of convertible preferred stock has a number of votes equal to the number of shares of common stock into which it is convertible. The holders of the convertible preferred stock shall vote together with the holders of common stock as a single class upon any matter submitted to stockholders for a vote or written consent.

Convertible preferred stockholders are entitled to vote in the election of board members based on the conversion of each preferred stock to common stock. The approval of the holders of (i) a majority of the voting power of the outstanding shares of convertible preferred stock, voting together as a single class and on an as-converted to common stock basis and (ii) a majority of the voting power of the outstanding shares of Series B convertible preferred stock, voting together as a single class on an as-converted-to-common-stock basis are required in order to take the following actions: amend or repeal any provisions in the charter or bylaws if it would adversely impact the convertible preferred stock holders, authorize, issue or obligate the issuance of options or shares (or securities convertible or exchangeable for options or shares) of any class superior to or on a parity with the convertible preferred stock, reclassify any common stock into shares having rights superior to or on a parity with the convertible preferred stock, increase the authorized number of shares of preferred stock, reduce the authorized number of members of the board of directors below three, and create or hold capital stock in any subsidiary not wholly owned by the Company, dispose of any capital stock of any subsidiary or permit any subsidiary to dispose of all or substantially all of the assets of such subsidiary.

Dividends

Holders of convertible preferred stock are entitled, when and as declared by the Company’s Board of Directors, to receive non-cumulative dividends that accrue at an annual rate of $0.26 per share of Series A convertible preferred stock and $0.53 per share of Series B convertible preferred stock. These convertible preferred stock dividends are payable in preference and priority to any payment of any dividend on shares of common stock.

Conversion

Any share of convertible preferred stock may, at the option of the holder, be converted at any time into such number of fully-paid as is determined by dividing $3.30 and $6.61 for the Series A convertible preferred stock and Series B convertible preferred stock, respectively, by the conversion price for such series in effect at the time of conversion. As of December 31, 2018, the Series A and Series B conversion prices equaled $3.30 and $6.61, respectively, and thus were convertible into common stock at a one-for-one basis. The conversion price for each series of convertible preferred stock is subject to an adjustment in the event of stock split, combination, common stock dividend or distribution, reclassification, exchange, substitution, or reorganization. The shares of convertible preferred stock are subject to anti-dilution protection if there are subsequent issuances of common stock without consideration or for a consideration per share less than the Series A conversion price in the case of Series A convertible preferred stock and the Series B conversion price in the case of Series B convertible preferred stock, in each case in effect immediately prior to the issuance of such additional share.

Each share of convertible preferred stock is automatically converted into common stock upon the earlier of the event of (i) the approval of at least 66 and 2/3 percent of the outstanding convertible preferred stock, or (ii) closing of an initial public offering where the price per share is not less than $14.54, adjusted for any stock splits, combinations, consolidations, or stock distributions or dividends, and the gross proceeds to the Company are not less than $20.0 million (Qualified IPO).

Liquidation

Upon any liquidation, dissolution, or winding up of the Company, whether voluntary or involuntary, before any distribution or payment shall be made to the holders of any common stock, the holders of convertible preferred stock shall be entitled to be paid out of the assets of the Company legally available for distribution for each share of convertible preferred stock held by them, an amount per share of convertible preferred stock equal to $3.30 per share and $6.61 per share, respectively, for each share of Series A convertible preferred stock and Series B convertible preferred stock held by them, as adjusted for stock splits, combinations, consolidations, or stock distributions or dividends, plus all declared and unpaid dividends thereon. If, upon any such liquidation event, the assets of the Company are insufficient to make payment in full to all holders of convertible preferred stock of the liquidation preference, then such assets shall be distributed among the holders of the convertible preferred stock at the time outstanding, ratably in proportion to the full amounts to which they would otherwise be respectively entitled. After completion of payment to the convertible preferred stock holders noted above, common stock holders will receive $0.01 per share for each share of common stock, or if the assets and funds are insufficient to permit the payment to such holders of the full aforesaid amount, then the entire assets and funds of the Company legally available for distribution shall be distributed ratably. Any remaining assets and funds, after payment of the preferential aforementioned amounts to the preferred and common, if the assets and funds are insufficient to permit the payment to such holders of the full aforesaid amount, then the entire assets and funds of the Company legally available for distribution shall be distributed ratably. Any remaining assets and funds, after payment of the preferential aforementioned amounts to the preferred and common, shall be distributed ratably among holders of common stock and preferred stock in proportion to the number of common stock that would be held by each shareholder if all convertible preferred stock were converted into common stock immediately prior to liquidation, dissolution, or winding up, utilizing the then conversion price. As of December 31, 2018, in the event of any liquidation, dissolution, winding up of the Company, the holders of Series A convertible preferred stock were entitled to receive an amount equal to $3.30 per share and the holders of Series B convertible preferred stock were entitled to receive an amount equal to $6.61 per share.

A liquidation transaction is deemed to occur if the Company (i) merges or consolidates with any other company, and the stockholders of the Company no longer own at least 50% of the voting power of the surviving entity, (ii) sells all or substantially all of the Company’s assets, and (iii) sells or disposes of one or more subsidiaries holding substantially all of the Company’s assets, to a party not owned by the Company.

Redemption

The convertible preferred stock is not redeemable.

During 2019, the Company issued 7,717,446 shares of Series C convertible preferred stock for total proceeds of $102.0 million. A portion of the shares of Series C convertible preferred stock was issued to satisfy the settlement of an unsecured promissory note amounting to $20.0 million.

Immediately prior to the closing of the IPO, all outstanding shares of the Company’s convertible preferred stock converted into 10,787,861 shares of common stock and 6,431,205 shares of non-voting common stock and the related carrying value was reclassified to common stock, non-voting common stock and additional paid-in capital. There were no shares of convertible preferred stock outstanding as of December 31, 2019.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 8. Stock-Based Compensation

2018 Omnibus Incentive Plan (as Amended and Restated)

The Company’s Board of Directors adopted and the Company’s stockholders approved, effective on the day prior to the effectiveness of the registration statement on Form S-1 related to the IPO, an amendment and restatement of the 2018 Omnibus Incentive Plan (the 2018 Plan) which provides for the grant of incentive stock options, within the meaning of Section 422 of the Code to employees, and for the grant of nonstatutory stock options, restricted stock, restricted stock units, stock appreciation rights, performance units, and performance shares to employees, directors, and consultants of the Company.

Options granted under the 2018 Plan expire no later than 10 years from the date of grant. The exercise price of options granted under the 2018 Plan must at least be equal to the fair market value of the Company’s common stock on the date of grant. With respect to any participant who owns more than 10% of the voting power of all classes of the Company’s outstanding stock, the term of an incentive stock option granted to such participant must not exceed five years and the exercise price must equal at least 110% of the fair market value on the grant date. Employee stock options generally vest 25% upon one year of continued service to the Company, with the remainder in monthly increments over three additional years.

Subject to an annual evergreen increase and adjustment in the case of certain capitalization events, the Company initially reserved 4,384,000 shares of the Company’s common stock for issuance pursuant to awards under the 2018 Plan. The 2018 Plan is administered by the Compensation Committee of the Company’s Board of Directors. The number of shares of the Company’s common stock available for issuance under the 2018 Plan will also include an annual increase on the first day of each fiscal year beginning with the 2020 fiscal year, equal to the least of (i) 8,768,800 shares, (ii) 4% of the Company’s common stock outstanding at December 31 of the immediately preceding year, or (iii) such number of shares as determined by the Company’s Board of Directors. As of December 31, 2019, 2,669,264 shares of common stock remained available for issuance under the 2018 Plan. Effective January 1, 2020, the number of shares of common stock available under the 2018 Plan increased by 964,487 shares pursuant to the evergreen provision of the 2018 Plan.

2010 Stock Plan (as Amended and Restated)

The 2010 Stock Plan (the 2010 Plan) was originally adopted by the Company’s Board of Directors and approved by the Company’s stockholders in November 2010. The 2010 Plan was amended in December 2017. The 2010 Plan allowed the Company to provide incentive stock options, within the meaning of Section 422 of the Code, nonstatutory stock options and stock purchase rights to eligible employees, consultants and directors and any parent or subsidiary of the Company. The 2010 Plan was terminated in 2019 and the Company will not grant any additional awards under the 2010 Plan. However, the 2010 Plan will continue to govern the terms and conditions of the outstanding awards previously granted under the 2010 Plan.

2019 Employee Stock Purchase Plan

The Company’s Board of Directors adopted and the Company’s stockholders approved, effective on the day prior to the effectiveness of the registration statement on Form S-1 related to the IPO, the 2019 Employee Stock Purchase Plan (ESPP). However, no offering period or purchase period under the ESPP will begin unless and until determined by the Company’s Board of Directors. The ESPP is intended to have two components: a component that is intended to qualify as an “employee stock purchase plan” under Section 423 of the Code (the 423 Component) and a component that is not intended to qualify (the Non-423 Component). The ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their eligible compensation. At the end of each offering period, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock at the beginning of the offering period or at the end of each applicable purchase period.

Subject to adjustment in the case of certain capitalization events, a total of 280,000 common shares of the Company were available for purchase at adoption of the ESPP. Pursuant to the ESPP, the annual share increase pursuant to the evergreen provision is determined based on the least of (i) 560,000 shares, (ii) 1% of the Company’s common stock outstanding at December 31 of the immediately preceding year, or (iii) such number of shares as determined by the Company’s Board of Directors. As of December 31, 2019, 280,000 shares of common stock remained available for issuance under the ESPP. Effective January 1, 2020, the number of shares of common stock available under the ESPP increased by 241,121 shares pursuant to the evergreen provision of the ESPP.

Stock-Based Compensation Expense

Total stock-based compensation expense recorded related to the 2010 Plan, 2018 Plan, and ESPP was recorded in the statements of operations and allocated as follows (in thousands):

	Year Ended December 31,
	2019		2018		2017
Research and development	$	522	$	51	$	35
General and administrative		492		132		58
Total stock-based compensation expense	$	1,014	$	183	$	93

Stock Options

The following table summarizes stock option activity:

				Outstanding Options
	Shares Available for Grant			Shares			Weighted- Average Exercise		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
											(in thousands)
Balance—December 31, 2018		456,818			1,523,285		$	1.16		7.9	$	347
Addition - Option pool		3,165,087
Granted		(974,181	)		974,181		$	6.36
Exercised		—			(184,036	)	$	0.98
Cancelled		21,540			(24,221	)	$	3.48
Balance—December 31, 2019		2,669,264			2,289,209		$	3.36		8.1	$	79,656
Exercisable – December 31, 2019					984,108		$	1.37		6.6	$	36,209

The fair value of employee stock options was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2019			2018			2017
Expected term in years		6.0			5.9			6.0
Expected volatility		79.3	%		77.5	%		73.2	%
Risk-free interest rate		2.2	%		2.9	%		2.1	%
Expected dividend yield		—			—			—
Weighted average fair value of share-based awards granted	$	4.4		$	0.9		$	0.7

As of December 31, 2019, there was $4.0 million of total unrecognized compensation cost related to stock options under the Plans. The unrecognized stock-based compensation cost is expected to be recognized over a weighted-average period of 3.4 years.

The fair value of ESPP was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2019			2018		2017
Expected term in years		0.7			—		—
Expected volatility		74.3	%		—		—
Risk-free interest rate		1.9	%		—		—
Expected dividend yield		—			—		—

Restricted Stock

During December 2018, the Company issued 116,518 shares of common stock to an executive officer under a restricted stock agreement at a grant date fair value of $1.39 per share that vests over two years. Any unvested shares are subject to forfeiture in the case that the grantee’s service terminates. As of December 31, 2019, 58,259 shares of restricted stock were vested. For the years ended December 31, 2019 and 2018, the related stock-based compensation was immaterial. As of December 31, 2019, there was $44,000 of unrecognized stock-based compensation related to restricted stock, which the Company expects to recognize over a remaining weighted-average period of 0.6 years.

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

Note 9. Income Taxes

Income Taxes

The Company had no income tax expense for the years ended December 31, 2019, 2018 and 2017. The following is a reconciliation of the statutory federal income tax rate to the Company’s effective tax rate:

	Year Ended December 31,
	2019			2018			2017
Federal tax (benefit) at statutory rate		21.0	%		21.0	%		34.0	%
State tax (benefit), net of federal benefit		6.7			5.5			4.9
Permanent differences and other		(0.4	)		(0.8	)		(1.5	)
Research and development credits		4.3			5.4			5.3
Provision to return adjustments		(2.8	)		—			—
Tax Cuts and Jobs Act impact		—			—			(4.3	)
Change in valuation allowance		(28.8	)		(31.1	)		(38.4	)
Effective income tax rate		—	%		—	%		—	%

Deferred tax assets and liabilities consist of the following (in thousands):

	December 31,
	2019			2018
Deferred tax assets:
Net operating loss carryforwards	$	15,650		$	7,076
Accrued liabilities and reserves		716			457
Stock-based compensation		253			150
Intangible assets		10,435			9,040
Operating lease liability		4,121			—
Research and development credits		4,991			3,023
Total deferred tax assets		36,166			19,746
Deferred tax liabilities:
Property and equipment		(167	)		(109	)
Right-of-use assets		(3,956	)		—
Total deferred tax liabilities		(4,123	)		(109	)
Valuation allowance		(32,043	)		(19,637	)
Net deferred tax assets	$	—		$	—

The provisions of ASC Topic 740, Accounting for Income Taxes (ASC 740), require an assessment of both positive and negative evidence when determining whether it is more likely than not that deferred tax assets are recoverable. For the years ended December 31, 2019 and 2018, based on all available objective evidence, including the existence of cumulative losses, the Company determined that it was not more likely than not that the net deferred tax assets were fully realizable. Accordingly, the Company established a full valuation allowance against its deferred tax assets. The Company intends to maintain a full valuation allowance on net deferred tax assets until sufficient positive evidence exists to support reversal of the valuation allowance. During the years ended December 31, 2019 and 2018, the valuation allowance increased by $12.4 million and $16.3 million, respectively.

At December 31, 2019, the Company had net operating loss carryforwards available to reduce future taxable income, if any, for federal and California income tax purposes of approximately $58.3 million and $48.6 million, respectively. Of the federal net operating loss carryforwards at December 31, 2019, $4.3 million begins expiring in 2030 and $53.9 million can be carried forward indefinitely, subject to an annual limitation of 80% of taxable income. The California net operating loss carryforward begins expiring in 2036.

At December 31, 2019, the Company also had federal and California research and development tax credit carryforwards of $4.4 million and $2.7 million, respectively, available to offset future income tax, if any. The federal credit carryforwards begins expiring in 2030, and the California credits can be carried forward indefinitely.

Under Section 382 and 383 of the Internal Revenue Code of 1986, as amended, if a corporation undergoes an “ownership change,” the corporation's ability to use its pre-change net operating loss carryforwards and other pre-change attributes, such as research tax credits, to offset its post-change income may be limited. In general, an “ownership change” will occur if there is a cumulative change in the Company's ownership by “5-percent shareholders” that exceeds 50 percentage points over a rolling three-year period. Similar rules may apply under state tax laws. Therefore, certain of the Company's carryforward tax attributes may be subject to an annual limitation regarding their utilization against taxable income in future periods. The Company has completed a Section 382 study and believes it has experienced two changes in ownership. As a result, the federal and California NOL carryforwards and tax credit carryforwards may expire before being applied to reduce future income tax liabilities.

Uncertain Tax Positions

The Company adopted the provisions of ASC 740, which requires companies to determine whether it is “more likely than not” that a tax position will be sustained upon examination by the appropriate taxing authorities before any tax benefit can be recorded in the financial statements. It also provides guidance on the recognition, measurement, classification and interest and penalties related to uncertain tax positions.

The following table summarizes the activity related to the Company’s gross unrecognized tax benefits (in thousands):

	December 31,
	2019		2018
Beginning balance	$	1,113	$	665
Additions for tax positions related to current year		707		448
Ending balance	$	1,820	$	1,113

The unrecognized tax benefits, if recognized, would not affect the effective income tax rate due to the valuation allowance that currently offsets deferred tax assets. Interest and penalties were zero. The Company does not expect the unrecognized tax benefits to change significantly over the next 12 months.

The Company files federal and California income tax returns. All periods since inception are subject to examination by federal and state authorities, where applicable. There are currently no pending income tax examinations.

Impact of the Tax Cuts and Jobs Act

The U.S. government enacted the Tax Cuts and Jobs Act (Tax Act) on December 22, 2017. The Tax Act incorporates broad and complex changes to the U.S. tax code. A main provision of the Tax Act reduces the corporate federal tax rate from a maximum rate of 34% to a flat rate of 21%, effective January 1, 2018. The Tax Act also contains a number of provisions that may impact the Company in future years.

As a result of the reduction in the corporate federal tax rate, the Company has remeasured its U.S. deferred tax assets and liabilities as of December 31, 2017 to reflect the lower rate expected to apply when these temporary differences reverse. The remeasurement resulted in a reduction in deferred tax assets of $0.5 million and a corresponding decrease in the valuation allowance.

As of December 31, 2018, the Company has completed its accounting for all of the enactment-date income tax effects of the Tax Act based upon the Company’s current interpretation of the Tax Act. The Company will continue to monitor ongoing guidance in this area, as the U.S. Treasury Department, the Internal Revenue Service (IRS), and other standard-setting bodies could interpret or issue guidance on how provisions of the Tax Act will be applied or otherwise administered that is different from the Company’s interpretation.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 10. Commitments and Contingencies

Operating Leases

During 2019, the Company early adopted ASC 842 and its associated amendments as of January 1, 2019 using the modified retrospective transition approach by applying the new standard to all leases existing at the date of the initial application and not restating comparative periods. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed the Company to carryforward the historical lease classification of those leases in place as of January 1, 2019. The impact of the adoption of ASC 842 was as follows (in thousands):

	Topic 840			Topic 842			Impact of Adoption
Balance Sheet	January 1, 2019			January 1, 2019			January 1, 2019
Deferred rent, current	$	(108	)	$	—		$	108
Deferred rent, non-current		—			—			—
Operating lease right-of-use asset		—			600			600
Lease liabilities, current		—			(708	)		(708	)
Lease liabilities, non-current		—			—			—

Prior to 2019, the Company recorded operating lease rent expense under ASC 840 on a straight-line basis over the non-cancelable lease term. Rent expense for years ended December 31, 2018, and 2017 was $0.7 million and $0.8 million, respectively. Future minimum lease payments as of December 31, 2018 are $0.7 million in 2019.

The Company leases its headquarters with its main offices and laboratory facilities in Mountain View, California under two lease agreements that end in September 2024 and April 2025. During the three months ended December 31, 2019, the Company entered into a sub-lease agreement for additional office and laboratory space in Mountain View, California, which commenced on December 1, 2019 and expires in September 2024. The Company determined the incremental borrowing rate for this sub-lease agreement based on an analysis of corporate bond yields with a credit rating similar to the Company.

Variable lease cost primarily relates to common area maintenance charges for its real estate leases, which is dependent on usage. Because the rate implicit in each lease is not readily determinable, the Company uses its incremental borrowing rate to determine the present value of the lease payments. As noted in “Note 11 - Related Party Transactions with its Significant Investor,” the Company entered into an agreement with the Significant Investor in February 2019 whereby the Significant Investor lent its credit and creditworthiness to the Company which applied to the Company’s leases that transitioned upon the adoption of ASC 842. At the time of adoption, the Company determined the incremental borrowing rates for its leases by adjusting the observable risk-free interest rate with a credit risk premium corresponding to the Significant Investor’s credit rating.

Information related to the Company’s ROU assets and related lease liabilities as well as components of the Company’s lease costs were as follows (in thousands except for remaining lease term and discount rate):

	Year Ended
	December 31, 2019
Cash paid for operating lease liabilities	$	1,527
Right-of-use asset recognized in exchange for new lease obligations		14,137
Current operating lease liabilities		2,483
Non-current operating lease liabilities		12,244
Operating lease cost		1,396
Variable lease cost		683
Weighted average remaining lease term in years		5.1
Weighted average discount rate		3.8	%

Maturities of lease liabilities as of December 31, 2019 were as follows (in thousands):

	Operating
	Lease
Year Ending December	Commitments
2020	$	3,002
2021		3,086
2022		3,172
2023		3,261
2024		3,008
Thereafter		733
Total		16,262
Less imputed interest		(1,535	)
Total lease liabilities	$	14,727

Employee Benefit Plan

The Company sponsors a 401(k) defined contribution plan for its employees. This plan provides for tax-deferred salary deductions for all employees. Employee contributions are voluntary. Employees may contribute up to 100% of their annual compensation to this plan, as limited by an annual maximum amount as determined by the IRS.

Legal Proceedings

The Company, from time to time, may be party to litigation arising in the ordinary course of business. The Company was not subject to any material legal proceedings during the years ended December 31, 2019 and 2018, and, to the best of its knowledge, no material legal proceedings are currently pending or threatened.

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 Delaware corporate law. The Company currently has directors’ and officers’ insurance.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

13. Selected Quarterly Financial Data (Unaudited)

The following tables provide the selected quarterly financial data for the years ended December 31, 2019 and 2018 (in thousands, except share and per share data):

	2019
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Statements of Operations Data:
Operating expenses:
Research and development	$	5,912		$	8,303		$	8,279		$	12,763
General and administrative		1,445			2,228			2,394			3,174
Total operating expenses		7,357			10,531			10,673			15,937
Loss from operations		(7,357	)		(10,531	)		(10,673	)		(15,937	)
Other income (expense), net		(113	)		(145	)		501			1,122
Net loss	$	(7,470	)	$	(10,676	)	$	(10,172	)	$	(14,815	)
Net loss per share, basic and diluted	$	(16.86	)	$	(19.08	)	$	(2.41	)	$	(0.49	)
Weighted-average common shares outstanding, basic and diluted		443,118			559,671			4,222,259			30,478,980

	2018
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Statements of Operations Data:
Operating expenses:
Research and development	$	2,526		$	3,450		$	5,172		$	7,814
General and administrative		430			794			1,373			1,232
Total operating expenses		2,956			4,244			6,545			9,046
Loss from operations		(2,956	)		(4,244	)		(6,545	)		(9,046	)
Other income (expense), net		30			29			28			(7	)
Net loss	$	(2,926	)	$	(4,215	)	$	(6,517	)	$	(9,053	)
Net loss per share, basic and diluted	$	(6.68	)	$	(9.62	)	$	(14.88	)	$	(20.67	)
Weighted-average common shares outstanding, basic and diluted		438,074			438,074			438,074			438,074

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP).
Reverse Stock Split	Reverse Stock Split In August 2019, the Company filed an amendment to the Company’s amended and restated certificate of incorporation to effect a reverse split of shares of the Company’s common stock, non-voting common stock and convertible preferred stock, each on a 6.6084-for-1 basis (Reverse Stock Split). The Reverse Stock Split also applied to any outstanding securities or rights convertible into, or exchangeable or exercisable for, common stock, non-voting common stock or convertible preferred stock. The par value of the common stock was not adjusted as a result of the Reverse Stock Split. All references to common stock, non-voting common stock, restricted stock, options to purchase common stock, share data, per share data, convertible preferred stock and related information contained in the financial statements and related footnotes have been retrospectively adjusted to reflect the effect of the Reverse Stock Split for all periods presented. The Reverse Stock Split was effected on August 30, 2019.
Initial Public Offering	Initial Public Offering On September 17, 2019, the Company’s registration statement on Form S-1 (File No. 333-233365) relating to its initial public offering (IPO) of common stock became effective. The IPO closed on September 20, 2019 at which time the Company issued an aggregate of 12,578,125 shares of its common stock at a price of $16.00 per share, including 1,640,625 shares issued in connection with the full exercise by the underwriters of their option to purchase additional shares of common stock. In addition, immediately prior to the closing of the IPO, all outstanding shares of the Company’s convertible preferred stock automatically converted into 10,787,861 shares of common stock and 6,431,205 shares of non-voting common stock. Proceeds from the IPO, net of underwriting discounts and commissions and offering costs, were approximately $183.0 million.
Liquidity	Liquidity The Company has incurred net operating losses and negative cash flows from operations since its inception and had an accumulated deficit of $107.2 million at December 31, 2019. As of December 31, 2019, the Company had cash and investments of $236.6 million. Management believes that the existing financial resources are sufficient to continue operating activities at least one year past the issuance date of these financial statements. The Company has historically financed its operations primarily through the sale of convertible preferred stock and common stock and the issuance of unsecured promissory notes. To date, none of the Company’s product candidates have been approved for sale, and the Company has not generated any revenue since inception. Management expects operating losses to continue and increase for the foreseeable future, as the Company progresses into clinical development activities for its lead product candidates. The Company’s prospects are subject to risks, expenses and uncertainties frequently encountered by companies in the biotechnology industry as discussed below. While the Company has been able to raise multiple rounds of financing, there can be no assurance that in the event the Company requires additional financing, such financing will be available on terms which are favorable or at all. Failure to generate sufficient cash flows from operations, raise additional capital or reduce certain discretionary spending would have a material adverse effect on the Company’s ability to achieve its intended business objectives.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company evaluates its estimates, including, but not limited to, those related to investments, manufacturing accruals, accrued research and development expenses, fair value of common stock, stock-based compensation, operating lease right-of-use (ROU) assets and liabilities, income tax uncertainties and the valuation of deferred tax assets. The Company bases its estimates on its historical experience and also on assumptions that it believes are reasonable; however, actual results could significantly differ from those estimates.
Segments	Segments The Company operates and manages its business as one reportable and operating segment, which is the business of developing engineered IgM antibodies for the treatment of cancer. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for allocating and evaluating financial performance. All long-lived assets are maintained in, and all losses are attributable to, the United States of America.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to a concentration of credit risk consist primarily of cash and investments. The Company invests in money market funds, U.S. Treasury securities, U.S. government agency securities, corporate debt and commercial paper. The Company maintains bank deposits in federally insured financial institutions and these deposits may exceed federally insured limits. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash and cash equivalents and issuers of investments to the extent recorded on the balance sheets. The Company’s investment policy limits investments to money market funds, certain types of debt securities issued by the U.S. Government and its agencies, corporate debt, commercial paper, and places restrictions on the credit ratings, maturities and concentration by type and issuer. The Company has not experienced any losses on its deposits of cash and investments. The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, the Company’s early stages of clinical drug development; uncertainties related to the use of engineered IgM antibodies, which is a novel and unproven therapeutic approach; the Company’s ability to advance product candidates into, and successfully complete, clinical trials on the timelines it projects; the Company’s ability to adequately demonstrate sufficient safety and efficacy of its product candidates; the Company’s ability to enroll patients in its ongoing and future clinical trials; the Company’s ability to successfully manufacture and supply its product candidates for clinical trials; the Company’s ability to obtain additional capital to finance its operations; uncertainties related to the projections of the size of patient populations suffering from the diseases the Company is targeting; the Company’s ability to obtain, maintain, and protect its intellectual property rights; developments relating to the Company’s competitors and its industry, including competing product candidates and therapies; general economic and market conditions; and other risks and uncertainties. The Company’s product candidates will require approvals from the U.S. Food and Drug Administration and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash and cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts and are stated at fair value. Restricted cash consisted of a money market account that served as collateral for a credit card agreement at one of the Company’s financial institutions.
Investments	Investments The Company’s investments have been classified and accounted for as available-for-sale securities. Fixed income securities consist of U.S. Treasury securities, U.S. government agency securities, corporate debt, and commercial paper. The specific identification method is used to determine the cost basis of fixed income securities sold. These securities are recorded on the balance sheets at fair value. Unrealized gains and losses on these securities are included as a separate component of accumulated other comprehensive income. The cost of investment securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion are included in other income, net. Realized gains and losses and declines in fair value judged to be other-than-temporary, if any, are also included in other income, net. The Company evaluates securities for other-than-temporary impairment at the balance sheet date. Declines in fair value determined to be other-than-temporary are also included in other income, net. The Company classifies its investments as short or long term primarily based on the remaining contractual maturity of the securities.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is determined using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or the estimated useful economic lives of the related assets. Upon retirement or sale of the assets, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss are recorded to the statements of operations. Repairs and maintenance are charged to operations as incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. The Company evaluates the carrying amount of its long-lived assets whenever events or changes in circumstances indicate that the assets may not be recoverable. An impairment loss would be recognized when estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount of the asset. There was no impairment of long-lived assets in 2019, 2018 and 2017.
Convertible Preferred Stock	Convertible Preferred Stock The Company records shares of convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs. The convertible preferred stock is recorded outside of stockholders’ deficit on the balance sheets because the shares contain liquidation features that are not solely within the Company’s control. The Company has elected not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because of the uncertainty of whether or when such an event would occur. Subsequent adjustments to increase the carrying values to the liquidation preferences will be made only when it becomes probable that such a liquidation event will occur.
Research and Development Expenses	Research and Development Expenses The Company expenses research and developments costs as they are incurred. Research and development expenses consist primarily of: (i) personnel-related expenses, including salaries, benefits and stock-based compensation expense, for personnel in the Company’s research and development functions; (ii) fees paid to third parties such as contractors, consultants and contract research organizations (CROs), for animal studies and other costs related to preclinical and clinical testing; (iii) costs related to acquiring and manufacturing research and clinical trial materials, including under agreements with third parties such as contract manufacturing organizations (CMOs), and other vendors; (iv) costs related to the preparation of regulatory submissions; (v) expenses related to laboratory supplies and services; and (vi) depreciation of equipment and facilities expenses.
Accrued Research and Development Expenses	Accrued Research and Development Expenses The Company records accruals for estimated costs of research, preclinical studies, clinical trials, and manufacturing, which are significant components of research and development expenses. A substantial portion of the Company’s ongoing research and development activities is conducted by third-party service providers, CROs and CMOs. The Company’s contracts with the CMOs generally include fees such as initiation fees, reservation fees, costs related to animal studies and safety tests, verification run costs, materials and reagents expenses, taxes, etc. The Company’s contracts with CROs generally include pass-through fees such as regulatory expenses, investigator fees, travel costs and other miscellaneous costs, including shipping and printing fees. The financial terms of these contracts are subject to negotiations, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company accrues the costs incurred under agreements with these third parties based on estimates of actual work completed in accordance with the respective agreements. The Company determines the estimated costs through discussions with internal personnel and external service providers as to the progress, or stage of completion or actual timeline (start-date and end-date) of the services and the agreed-upon fees to be paid for such services. In the event the Company makes advance payments, the payments are recorded as a prepaid expense and recognized as the services are performed. As actual costs become known, the Company adjusts its accruals. Although the Company does not expect its estimates to be materially different from amounts actually incurred, such estimates for the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in us reporting amounts that are too high or too low in any particular period. The Company’s accrual is dependent, in part, upon the receipt of timely and accurate reporting from CROs and other third-party vendors. Variations in the assumptions used to estimate accruals including, but not limited to, the number of patients enrolled, the rate of patient enrollment and the actual services performed, may vary from the Company’s estimates, resulting in adjustments to clinical trial expenses in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect its financial condition and results of operations. Through December 31, 2019, there have been no material differences from the Company’s estimated accrued research and development expenses to actual expenses.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation by measuring and recognizing compensation expense for all share-based awards made to employees, non-employees and directors based on estimated grant-date fair values. The Company uses the straight-line method to allocate compensation cost to reporting periods over the requisite service period, which is generally the vesting period, and estimates the fair value of share-based awards to employees and directors using the Black-Scholes option-pricing model. The Company accounts for forfeitures as they occur. The fair value of each purchase under the employee stock purchase plan (ESPP) is estimated at the beginning of the offering period using the Black-Scholes option pricing model and recorded as expense over the service period using the straight-line method.
Net Loss Per Share	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 (including non-voting common stock) outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.
Deferred Offering Costs	Deferred Offering Costs Deferred offering costs, consisting of legal, accounting, and filing fees directly relating to the IPO, were capitalized and offset against the IPO proceeds upon the completion of the offering. For the year ended December 31, 2018, there were no offering costs incurred. Upon completion of the IPO, approximately $4.3 million of deferred offering costs were offset against the IPO proceeds in additional paid-in capital.
Leases	Leases During 2019, the Company elected to early adopt Accounting Standard Update (ASU) No. 2016-02, Leases (ASC 842) and its associated amendments as of January 1, 2019 using the modified retrospective transition approach. There was no cumulative-effect adjustment recorded to accumulated deficit upon adoption. Under ASC 842, the Company determines if an arrangement is a lease at inception. In addition, the Company determines whether leases meet the classification criteria of a finance or operating lease at the lease commencement date considering: (1) whether the lease transfers ownership of the underlying asset to the lessee at the end of the lease term, (2) whether the lease grants the lessee an option to purchase the underlying asset that the lessee is reasonably certain to exercise, (3) whether the lease term is for a major part of the remaining economic life of the underlying asset, (4) whether the present value of the sum of the lease payments and residual value guaranteed by the lessee equals or exceeds substantially all of the fair value of the underlying asset, and (5) whether the underlying asset is of such a specialized nature that it is expected to have no alternative use to the lessor at the end of the lease term. As of December 31, 2019, the Company's lease population consisted of real estate. As of the date of adoption of ASC 842 and December 31, 2019, the Company did not have finance leases. Operating leases are included in operating lease right-of-use (ROU) assets, lease liabilities, current, and lease liabilities, non-current in the Company’s balance sheet. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date if the rate implicit in the lease is not readily determinable. The Company determines the incremental borrowing rate base on an analysis of corporate bond yields with a credit rating similar to the Company. The determination of the Company’s incremental borrowing rate requires management judgment including the development of a synthetic credit rating and cost of debt as the Company currently does not carry any debt. The Company believes that the estimates used in determining the incremental borrowing rate are reasonable based upon current facts and circumstances. Applying different judgments to the same facts and circumstances could result in the estimated amounts to vary. The operating lease ROU assets also include adjustments for prepayments and accrued lease payments and exclude lease incentives. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise such options. Operating lease cost is recognized on a straight-line basis over the expected lease term. Lease agreements entered into after the adoption of ASC 842 that include lease and non-lease components are accounted for as a single lease component. Lease agreements with a noncancelable term of less than 12 months are not recorded on the Company’s balance sheet. For more information about the impact of adoption and disclosures on the Company’s leases, refer to “Note 10 – Commitments and Contingencies.”
Income Taxes	Income Taxes The Company accounts for income taxes using the liability method, whereby deferred tax asset and liability account balances are determined based on differences between the financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company provides a valuation allowance when it is more likely than not that some portion, or all of the Company’s deferred tax assets will not be realized. The Company accounts for income tax contingencies using a benefit recognition model. If it considers that a tax position is more likely than not to be sustained upon audit, based solely on the technical merits of the position, it recognizes the benefit. The Company measures the benefit by determining the amount that is greater than 50% likely of being realized upon settlement, presuming that the tax position is examined by the appropriate taxing authority that has full knowledge of all relevant information. 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 or penalties charged in relation to the unrecognized tax benefits.
Recently Adopted Accounting Standards and Accounting Pronouncements	Recently Adopted Accounting Standards During 2019, the Company elected to early adopt ASC 842 and its associated amendments as of January 1, 2019 using the modified retrospective transition approach by applying the new standard to all leases existing at the date of initial application and not restating comparative periods. There was no cumulative-effect adjustment recorded to accumulated deficit upon adoption. Under ASC 842, a lessee is required to recognize a lease liability and ROU asset for all leases. The new guidance also modified the classification criteria and requires additional disclosures to enable users of financial statements to understand the amount, timing, and uncertainty of cash flows arising from leases. Consistent with current guidance, a lessee’s recognition, measurement, and presentation of expenses and cash flows arising from a lease continue to depend primarily on its classification. The Company elected the package of three practical expedients permitted under the transition guidance, which allowed the Company to carryforward its historical lease classification, its assessment on whether a contract was or contains a lease, and its initial direct costs for any leases that existed prior to January 1, 2019. In addition, the Company elected the following transitional practical expedients: (1) the short-term lease exception and (2) to not separate its non-lease components for its real estate leases. The impact of adoption and additional disclosures required by the ASU have been included in “Significant Accounting Policies - Leases” above and in “Note 10 – Commitments and Contingencies.” In June 2018, the FASB issued ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting. This ASU simplifies the accounting for share-based awards to nonemployees by aligning it with the accounting for share-based awards to employees, with certain exceptions. This ASU is effective for annual periods beginning after December 15, 2019, and interim periods within annual periods beginning after December 15, 2020. Early adoption is permitted. The Company adopted this ASU as of January 1, 2019 and the adoption did not have a material impact on its financial statements and related disclosures. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. This ASU also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. This ASU is effective for fiscal years beginning after December 15, 2022 and interim periods within those fiscal years. Early adoption is permitted. The Company is currently assessing the impact of this standard on its financial statements and related disclosures. In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, which amends ASC 820, Fair Value Measurement. This ASU modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. The effective date is the first quarter of fiscal year 2020, with early adoption permitted for the removed disclosures and delayed adoption until fiscal year 2020 permitted for the new disclosures. The removed and modified disclosures will be adopted on a retrospective basis and the new disclosures will be adopted on a prospective basis. The Company is currently assessing the impact of this standard on its financial statements and related disclosures. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard will be effective beginning January 1, 2021. The Company is currently assessing the impact of this standard on its financial statements and related disclosures.

Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Summary of Investments Measured and Recognized at Fair Value

As of December 31, 2019, investments measured and recognized at fair value are as follows (in thousands):

		December 31, 2019
	Fair Value Hierarchy Level	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Investments
U.S. Treasury securities	Level 1	$	66,244	$	48	$	—		$	66,292
Corporate bonds	Level 2		39,953		3		—			39,956
Commercial paper	Level 2		74,507		—		(9	)		74,498
U.S. government agency securities	Level 2		19,969		1		—			19,970
Total		$	200,673	$	52	$	(9	)	$	200,716

Summary of Contractual Maturities of Investments

The following table presents the contractual maturities of the Company’s investments as of December 31, 2019 (in thousands):

	December 31, 2019
Due in less than one year	$	188,743
Due in more than one year		11,973
Total	$	200,716

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recorded related to the 2010 Plan, 2018 Plan, and ESPP was recorded in the statements of operations and allocated as follows (in thousands):

	Year Ended December 31,
	2019		2018		2017
Research and development	$	522	$	51	$	35
General and administrative		492		132		58
Total stock-based compensation expense	$	1,014	$	183	$	93

Summary of Stock Option

The following table summarizes stock option activity:

				Outstanding Options
	Shares Available for Grant			Shares			Weighted- Average Exercise		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
											(in thousands)
Balance—December 31, 2018		456,818			1,523,285		$	1.16		7.9	$	347
Addition - Option pool		3,165,087
Granted		(974,181	)		974,181		$	6.36
Exercised		—			(184,036	)	$	0.98
Cancelled		21,540			(24,221	)	$	3.48
Balance—December 31, 2019		2,669,264			2,289,209		$	3.36		8.1	$	79,656
Exercisable – December 31, 2019					984,108		$	1.37		6.6	$	36,209

Summary of Fair Value of Employee Stock Options Estimated Weighted-average Assumptions

The fair value of employee stock options was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2019			2018			2017
Expected term in years		6.0			5.9			6.0
Expected volatility		79.3	%		77.5	%		73.2	%
Risk-free interest rate		2.2	%		2.9	%		2.1	%
Expected dividend yield		—			—			—
Weighted average fair value of share-based awards granted	$	4.4		$	0.9		$	0.7

Summary of Fair Value of Employee Stock Purchase Plan Estimated Weighted-average Assumptions

The fair value of ESPP was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2019			2018		2017
Expected term in years		0.7			—		—
Expected volatility		74.3	%		—		—
Risk-free interest rate		1.9	%		—		—
Expected dividend yield		—			—		—

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Reconciliation of Statutory Federal Income Tax Rate

The following is a reconciliation of the statutory federal income tax rate to the Company’s effective tax rate:

	Year Ended December 31,
	2019			2018			2017
Federal tax (benefit) at statutory rate		21.0	%		21.0	%		34.0	%
State tax (benefit), net of federal benefit		6.7			5.5			4.9
Permanent differences and other		(0.4	)		(0.8	)		(1.5	)
Research and development credits		4.3			5.4			5.3
Provision to return adjustments		(2.8	)		—			—
Tax Cuts and Jobs Act impact		—			—			(4.3	)
Change in valuation allowance		(28.8	)		(31.1	)		(38.4	)
Effective income tax rate		—	%		—	%		—	%

Schedule of Deferred Tax Assets and Liabilities

Deferred tax assets and liabilities consist of the following (in thousands):

	December 31,
	2019			2018
Deferred tax assets:
Net operating loss carryforwards	$	15,650		$	7,076
Accrued liabilities and reserves		716			457
Stock-based compensation		253			150
Intangible assets		10,435			9,040
Operating lease liability		4,121			—
Research and development credits		4,991			3,023
Total deferred tax assets		36,166			19,746
Deferred tax liabilities:
Property and equipment		(167	)		(109	)
Right-of-use assets		(3,956	)		—
Total deferred tax liabilities		(4,123	)		(109	)
Valuation allowance		(32,043	)		(19,637	)
Net deferred tax assets	$	—		$	—

Summary of Gross Unrecognized Tax Benefits

The following table summarizes the activity related to the Company’s gross unrecognized tax benefits (in thousands):

	December 31,
	2019		2018
Beginning balance	$	1,113	$	665
Additions for tax positions related to current year		707		448
Ending balance	$	1,820	$	1,113

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Schedule of Impact of Adoption of Accounting Standards Update

The impact of the adoption of ASC 842 was as follows (in thousands):

	Topic 840			Topic 842			Impact of Adoption
Balance Sheet	January 1, 2019			January 1, 2019			January 1, 2019
Deferred rent, current	$	(108	)	$	—		$	108
Deferred rent, non-current		—			—			—
Operating lease right-of-use asset		—			600			600
Lease liabilities, current		—			(708	)		(708	)
Lease liabilities, non-current		—			—			—

Schedule of ROU Assets and Related Lease Liabilities

	Year Ended
	December 31, 2019
Cash paid for operating lease liabilities	$	1,527
Right-of-use asset recognized in exchange for new lease obligations		14,137
Current operating lease liabilities		2,483
Non-current operating lease liabilities		12,244
Operating lease cost		1,396
Variable lease cost		683
Weighted average remaining lease term in years		5.1
Weighted average discount rate		3.8	%

Schedule of Maturities of Lease Liabilities

Maturities of lease liabilities as of December 31, 2019 were as follows (in thousands):

	Operating
	Lease
Year Ending December	Commitments
2020	$	3,002
2021		3,086
2022		3,172
2023		3,261
2024		3,008
Thereafter		733
Total		16,262
Less imputed interest		(1,535	)
Total lease liabilities	$	14,727

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Schedule of Computation of Basic and Diluted Net Loss Per Share

The following table sets forth the computation of the basic and diluted net loss per share (in thousands except share and per share data):

	Year Ended December 31,
	2019			2018			2017
Numerator:
Net loss	$	(43,133	)	$	(22,711	)	$	(11,054	)
Denominator:
Weighted average common shares outstanding used to compute net loss per share, basic and diluted		8,995,410			438,074			437,942
Net loss per share attributable to common stockholders	$	(4.80	)	$	(51.84	)	$	(25.24	)

Summary of Potentially Dilutive Securities Not Included in the Diluted Per Share Calculations

Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:

	December 31,
	2019		2018
Series A convertible preferred stock		—		401,004
Series B convertible preferred stock		—		9,100,616
Restricted stock		58,259		116,518
Stock options		2,289,209		1,523,285
Total		2,347,468		11,141,423

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data

The following tables provide the selected quarterly financial data for the years ended December 31, 2019 and 2018 (in thousands, except share and per share data):

	2019
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Statements of Operations Data:
Operating expenses:
Research and development	$	5,912		$	8,303		$	8,279		$	12,763
General and administrative		1,445			2,228			2,394			3,174
Total operating expenses		7,357			10,531			10,673			15,937
Loss from operations		(7,357	)		(10,531	)		(10,673	)		(15,937	)
Other income (expense), net		(113	)		(145	)		501			1,122
Net loss	$	(7,470	)	$	(10,676	)	$	(10,172	)	$	(14,815	)
Net loss per share, basic and diluted	$	(16.86	)	$	(19.08	)	$	(2.41	)	$	(0.49	)
Weighted-average common shares outstanding, basic and diluted		443,118			559,671			4,222,259			30,478,980

	2018
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Statements of Operations Data:
Operating expenses:
Research and development	$	2,526		$	3,450		$	5,172		$	7,814
General and administrative		430			794			1,373			1,232
Total operating expenses		2,956			4,244			6,545			9,046
Loss from operations		(2,956	)		(4,244	)		(6,545	)		(9,046	)
Other income (expense), net		30			29			28			(7	)
Net loss	$	(2,926	)	$	(4,215	)	$	(6,517	)	$	(9,053	)
Net loss per share, basic and diluted	$	(6.68	)	$	(9.62	)	$	(14.88	)	$	(20.67	)
Weighted-average common shares outstanding, basic and diluted		438,074			438,074			438,074			438,074

Organization - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Sep. 20, 2019 USD ($) $ / shares shares	Aug. 31, 2019	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)
Subsidiary Sale Of Stock [Line Items]
Reverse stock split ratio		6.6084
Reverse stock split ratio, description			6.6084-for-1
Proceeds from IPO, net of underwriting discounts and commission and offering costs \| $			$ 187,162
Accumulated deficit \| $			107,205	$ 64,072
Cash, and investments \| $			$ 236,600
Non-voting Common Stock
Subsidiary Sale Of Stock [Line Items]
Conversion of convertible preferred stock into common stock, shares	6,431,205		6,431,205
Common Stock
Subsidiary Sale Of Stock [Line Items]
Common stock, shares issued			7,566
Conversion of convertible preferred stock into common stock, shares	10,787,861		10,787,861
IPO
Subsidiary Sale Of Stock [Line Items]
Common stock, shares issued	12,578,125
Common stock, price per share \| $ / shares	$ 16.00
Common stock, exercised by underwriters	1,640,625
Proceeds from IPO, net of underwriting discounts and commission and offering costs \| $	$ 183,000
IPO \| Non-voting Common Stock
Subsidiary Sale Of Stock [Line Items]
Conversion of convertible preferred stock into common stock, shares	6,431,205
IPO \| Common Stock
Subsidiary Sale Of Stock [Line Items]
Common stock, shares issued			12,578,125
Conversion of convertible preferred stock into common stock, shares	10,787,861

Convertible Preferred Stock - Additional Information (Details)		1 Months Ended		12 Months Ended
	Sep. 20, 2019 USD ($) $ / shares shares	Aug. 31, 2019	Oct. 31, 2018 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 shares
Temporary Equity [Line Items]
Common stock, shares outstanding			438,074	24,053,921	438,074
Convertible preferred stock, shares outstanding				0	9,501,620
Stock-based compensation expense \| $				$ 1,014,000	$ 183,000	$ 93,000
Convertible into common stock ratio		6.6084
Proceeds from initial public offering \| $				$ 187,162,000
Common stock liquidation preference per share \| $ / shares					$ 0.01
Common Stock
Temporary Equity [Line Items]
Conversion of convertible preferred stock into common stock, shares	10,787,861			10,787,861
IPO
Temporary Equity [Line Items]
Common stock, price per share \| $ / shares	$ 16.00
Proceeds from initial public offering \| $	$ 183,000,000
IPO \| Common Stock
Temporary Equity [Line Items]
Conversion of convertible preferred stock into common stock, shares	10,787,861
Minimum
Temporary Equity [Line Items]
Percentage of outstanding convertible preferred stock					66.67%
Maximum \| IPO
Temporary Equity [Line Items]
Common stock, price per share \| $ / shares					$ 14.54
Proceeds from initial public offering \| $					$ 20,000
Series B Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock shares issued					3,116,823
Proceeds from issuance of preferred stock \| $					$ 20,100,000
Convertible preferred stock, shares outstanding			9,100,616
Dividends annual rate \| $ / shares					$ 0.53
Conversion price per share \| $ / shares					$ 6.61
Convertible into common stock ratio					1
Liquidation preference per share \| $ / shares					$ 6.61
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares outstanding			401,004
Dividends annual rate \| $ / shares					0.26
Conversion price per share \| $ / shares					$ 3.30
Convertible into common stock ratio					1
Liquidation preference per share \| $ / shares					$ 3.30
Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock shares issued				7,717,446	3,116,823	1,210,580
Convertible preferred stock, shares outstanding				0	9,501,620	6,384,797	5,238,771
Stock-based compensation expense \| $			$ 0
Series C Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock shares issued				7,717,446
Proceeds from issuance of preferred stock \| $				$ 102,000,000
Debt settled \| $				$ 20,000,000
Non-voting Common Stock
Temporary Equity [Line Items]
Common stock, shares outstanding				6,431,205	0
Conversion of convertible preferred stock into common stock, shares	6,431,205			6,431,205
Non-voting Common Stock \| IPO
Temporary Equity [Line Items]
Conversion of convertible preferred stock into common stock, shares	6,431,205

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Jan. 01, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance	11,598,241	5,296,732
Shares available for issuance	456,818	2,669,264
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation		$ 4,000,000
Expects to recognize over a remaining weighted-average period		3 years 4 months 24 days
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expects to recognize over a remaining weighted-average period		7 months 6 days
Unrecognized stock-based compensation		$ 44,000
Executive Officer \| Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	2 years
Issued of common stock	116,518
Grant date fair value per share	$ 1.39
Shares vested		58,259
2018 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of exercise price of stock option on estimated fair value of shares		110.00%
Vesting period		3 years
Shares reserved for issuance		4,384,000
Outstanding stock percent		4.00%
Shares available for issuance		2,669,264
2018 Plan \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in number of shares			964,487
2018 Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Term of options		10 years
Increase in number of shares		8,768,800
2018 Plan \| Share-based Compensation Award, Tranche One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage		25.00%
Vesting period		1 year
2018 Plan \| 10% Stockholder \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Term of options		5 years
2018 Plan \| 10% Stockholder \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of voting power		10.00%
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding stock percent		1.00%
Shares available for issuance		280,000
Percentage of exercise price of stock option on estimated fair value of shares		85.00%
ESPP \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in number of shares			241,121
ESPP \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in number of shares		560,000
Discount rate		15.00%

Stock-Based Compensation - Summary of Stock Option (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding Options, Shares Available for Grant, Beginning balance	456,818
Outstanding Options, Shares Available for Grant, Addition - Option pool	3,165,087
Outstanding Options, Shares Available for Grant, Granted	(974,181)
Outstanding Options, Shares Available for Grant, Cancelled	21,540
Outstanding Options, Shares Available for Grant, Ending balance	2,669,264	456,818
Outstanding Options, Shares, Beginning balance	1,523,285
Outstanding Options, Shares, Granted	974,181
Outstanding Options, Shares, Exercised	(184,036)
Outstanding Options, Shares, Cancelled	(24,221)
Outstanding Options, Shares, Ending balance	2,289,209	1,523,285
Outstanding Options, Shares, Exercisable	984,108
Outstanding Options, Weighted-Average Exercise Price, Beginning balance	$ 1.16
Outstanding Options, Weighted-Average Exercise Price, Granted	6.36
Outstanding Options, Weighted-Average Exercise Price, Exercised	0.98
Outstanding Options, Weighted-Average Exercise Price, Canceled	3.48
Outstanding Options, Weighted-Average Exercise Price, Ending balance	3.36	$ 1.16
Outstanding Options, Weighted-Average Exercise Price, Exercisable	$ 1.37
Outstanding Options, Weighted Average Remaining Contractual Term (Years)	8 years 1 month 6 days	7 years 10 months 24 days
Outstanding Options, Weighted Average Remaining Contractual Term (Years), Exercisable	6 years 7 months 6 days
Outstanding Options, Aggregate Intrinsic Value, Beginning balance	$ 347
Outstanding Options, Aggregate Intrinsic Value, Ending balance	79,656	$ 347
Outstanding Options, Aggregate Intrinsic Value, Exercisable	$ 36,209

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax [Line Items]
Income tax expense	$ 0	$ 0	$ 0
Increase in valuation allowance amount	$ 12,400,000	16,300,000
Operating loss carryforwards limitations on use, percentage of taxable income	80.00%
Research and development credits	$ 4,991,000	$ 3,023,000
Interest or penalties charged in relation to unrecognized tax benefits	$ 0
Corporate federal tax rate	21.00%	21.00%	34.00%
Reduction in deferred tax assets	$ (500,000)
Decrease in valuation allowance	(500,000)
Federal
Income Tax [Line Items]
Operating loss carryforwards	58,300,000
Operating loss carryforwards, subject to expiration	$ 4,300,000
Operating loss carryforwards expiration year	2030
Operating loss carryforwards, not subject to expiration	$ 53,900,000
Research and development credits	$ 4,400,000
Federal credit carryforwards expiration period	2030
California
Income Tax [Line Items]
Operating loss carryforwards	$ 48,600,000
Operating loss carryforwards expiration year	2036
Research and development credits	$ 2,700,000

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 15,650	$ 7,076
Accrued liabilities and reserves	716	457
Stock-based compensation	253	150
Intangible assets	10,435	9,040
Operating lease liability	4,121
Research and development credits	4,991	3,023
Total deferred tax assets	36,166	19,746
Deferred tax liabilities:
Property and equipment	(167)	(109)
Right-of-use assets	(3,956)
Total deferred tax liabilities	(4,123)	(109)
Valuation allowance	$ (32,043)	$ (19,637)

Related Party Transactions with its Significant Investor - Additional Information (Details) - USD ($)		1 Months Ended		4 Months Ended	12 Months Ended
	Sep. 20, 2019	Jun. 30, 2019	Apr. 30, 2019	Apr. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Interest paid						$ 27,000
IPO
Related Party Transaction [Line Items]
Issuance of common stock, shares	12,578,125
Common Stock
Related Party Transaction [Line Items]
Issuance of common stock, shares					7,566
Shares issued upon conversion of convertible preferred stock	10,787,861				10,787,861
Common Stock \| IPO
Related Party Transaction [Line Items]
Issuance of common stock, shares					12,578,125
Shares issued upon conversion of convertible preferred stock	10,787,861
Non-voting Common Stock
Related Party Transaction [Line Items]
Shares issued upon conversion of convertible preferred stock	6,431,205				6,431,205
Non-voting Common Stock \| IPO
Related Party Transaction [Line Items]
Shares issued upon conversion of convertible preferred stock	6,431,205
Haldor Topsøe Holding A/S and Holdco
Related Party Transaction [Line Items]
Proceeds from related party notes receivable			$ 2,500,000
Haldor Topsøe Holding A/S and Holdco \| Common Stock \| IPO
Related Party Transaction [Line Items]
Issuance of common stock, shares	1,250,000				10,289,453
Haldor Topsøe Holding A/S and Holdco \| Series C Convertible Preferred Stock
Related Party Transaction [Line Items]
Preferred stock issued		2,269,838
Preferred stock issued, value		$ 30,000,000
Debt settled		20,000,000
Haldor Topsøe Holding A/S and Holdco \| Non-voting Common Stock \| IPO
Related Party Transaction [Line Items]
Shares issued upon conversion of convertible preferred stock	2,269,838
Haldor Topsøe Holding A/S and Holdco \| Unsecured Promissory Note
Related Party Transaction [Line Items]
Proceeds from loan from related party				$ 15,000,000
Outstanding unsecured promissory note		$ 20,000,000
Interest paid					$ 300,000

Fair Value Measurement - Summary of Investments Measured and Recognized at Fair Value (Details) - Fair Value, Recurring - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 200,673,000
Gross Unrealized Gains	52,000
Gross Unrealized Losses	(9,000)
Fair Value	200,716,000	$ 0
U.S. Treasury Securities \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	66,244,000
Gross Unrealized Gains	48,000
Fair Value	66,292,000
Corporate Bond \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	39,953,000
Gross Unrealized Gains	3,000
Fair Value	39,956,000
Commercial Paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	74,507,000
Gross Unrealized Losses	(9,000)
Fair Value	74,498,000
U.S. Government Agency Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	19,969,000
Gross Unrealized Gains	1,000
Fair Value	$ 19,970,000

Fair Value Measurement - Additional Information (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments measured and recognized at fair value	$ 200,716,000	$ 0

Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 5,146	$ 2,139
Less: Accumulated depreciation	(1,264)	(667)
Total property and equipment, net	3,882	1,472
Laboratory Equipment
Property Plant And Equipment [Line Items]
Total property and equipment, gross	3,800	1,987
Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment, gross	150	127
Leasehold Improvement
Property Plant And Equipment [Line Items]
Total property and equipment, gross	78	$ 25
Construction In Progress
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 1,118

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Depreciation expense	$ 597	$ 278	$ 161

Balance Sheet Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Accrued research and development materials and services	$ 906	$ 2,395
Accrued professional services	360	563
Accrued compensation	2,030	177
Other	9	447
Total accrued liabilities	$ 3,305	$ 3,582

Statements of Operations - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Statements of Operations - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses:
Research and development	$ 12,763	$ 8,279	$ 8,303	$ 5,912	$ 7,814	$ 5,172	$ 3,450	$ 2,526	$ 35,257	$ 18,962	$ 8,639
General and administrative	3,174	2,394	2,228	1,445	1,232	1,373	794	430	9,241	3,829	2,508
Total operating expenses	15,937	10,673	10,531	7,357	9,046	6,545	4,244	2,956	44,498	22,791	11,147
Loss from operations	(15,937)	(10,673)	(10,531)	(7,357)	(9,046)	(6,545)	(4,244)	(2,956)	(44,498)	(22,791)	(11,147)
Other income, net	1,122	501	(145)	(113)	(7)	28	29	30	1,365	80	93
Net loss	$ (14,815)	$ (10,172)	$ (10,676)	$ (7,470)	$ (9,053)	$ (6,517)	$ (4,215)	$ (2,926)	$ (43,133)	$ (22,711)	$ (11,054)
Net loss per share, basic and diluted	$ (0.49)	$ (2.41)	$ (19.08)	$ (16.86)	$ (20.67)	$ (14.88)	$ (9.62)	$ (6.68)	$ (4.80)	$ (51.84)	$ (25.24)
Weighted-average common shares outstanding, basic and diluted	30,478,980	4,222,259	559,671	443,118	438,074	438,074	438,074	438,074	8,995,410	438,074	437,942

Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
Statements of Comprehensive Loss - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (43,133)	$ (22,711)	$ (11,054)
Other comprehensive income:
Unrealized gain on investments	43
Comprehensive loss	$ (43,090)	$ (22,711)	$ (11,054)

Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
IPO
Stock issuance cost	$ 4.3
Series B Convertible Preferred Stock
Stock issuance cost		$ 0.5
Series C Convertible Preferred Stock
Stock issuance cost	$ 0.4

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of reportable segment \| Segment	1
Number of operating segment \| Segment	1
Impairment of long-lived assets	$ 0	$ 0	$ 0
Interest or penalties charged in relation to unrecognized tax benefits	0
IPO
Summary Of Significant Accounting Policies [Line Items]
Deferred offering costs	$ 4,300,000	$ 0
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life	3 years
Description of income tax contingencies, likely of being realized upon settlement	The Company measures the benefit by determining the amount that is greater than 50% likely of being realized upon settlement, presuming that the tax position is examined by the appropriate taxing authority that has full knowledge of all relevant information.
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life	5 years

Fair Value Measurement - Summary of Contractual Maturities of Investments (Details) - Fair Value, Recurring - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Due in less than one year	$ 188,743,000
Due in more than one year	11,973,000
Total	$ 200,716,000	$ 0

License Agreements - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 31, 2018
Research and Development Expenses \| LakePharma, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License expenses recognized		$ 100,000	$ 300,000	$ 0
Maximum \| LakePharma, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential payments based on achievement of specified development and regulatory milestones					$ 10,300,000
Adimab \| Research and Development Expenses
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License expenses recognized		$ 100,000	$ 300,000	$ 0
Adimab \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License fee	$ 1,000,000
Additional milestone payment	16,000,000
Adimab \| Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payment	$ 7,400,000

Common Stock and Non-Voting Common Stock - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) Vote $ / shares shares	Dec. 31, 2018 $ / shares shares
Class Of Stock [Line Items]
Common stock, shares authorized	1,000,000,000	30,264,511
Preferred stock, shares authorized	200,000,000	0
Common stock, par value \| $ / shares	$ 0.01	$ 0.01
Preferred stock, par value \| $ / shares	$ 0.01	$ 0.01
Common stock, voting rights	Each share of common stock is entitled to one vote
Number of common stock voting rights held \| Vote	1
Common stock, dividends declared \| $	$ 0
Common Stock Including Nonvoting Common Stock
Class Of Stock [Line Items]
Common stock, shares authorized	1,006,431,208
Non-voting Common Stock
Class Of Stock [Line Items]
Common stock, shares authorized	6,431,208	0
Common stock, par value \| $ / shares	$ 0.01	$ 0.01

Common Stock and Non-Voting Common Stock - Schedule of Number of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Stockholders Equity Note [Abstract]
Preferred stock, issued and outstanding		9,501,620
Restricted stock, issued and outstanding	58,259	116,518
Stock options, issued and outstanding	2,289,209	1,523,285
Stock options, future issuance	2,669,264	456,818
Employee stock purchase plan, available for future grants	280,000
Total	5,296,732	11,598,241

Commitments and Contingencies - Schedule of Impact of Adoption of Accounting Standard Update (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Lessee Lease Description [Line Items]
Deferred rent, current		$ (108)	$ (108)
Operating lease right-of-use asset	$ 14,137	600
Lease liabilities, current	(2,483)	(708)
Lease liabilities, non-current	$ 12,244
Impact of Adoption
Lessee Lease Description [Line Items]
Operating lease right-of-use asset		600
Lease liabilities, current		(708)
Deferred rent, current		$ 108

Commitments and Contingencies - Additional Information (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019 Agreement	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Lessee Lease Description [Line Items]
Operating lease future minimum payments in 2019			$ 0.7
Rent expense			$ 0.7	$ 0.8
Number of lease agreements \| Agreement		2
Percentage of employees contribution to annual compensation plan		100.00%
Offices and Laboratory \| Mountain View, California
Lessee Lease Description [Line Items]
Sub-lease commenced date	Dec. 01, 2019
Sub-lease expiration period month and year	2024-09
Offices and Laboratory \| Mountain View, California \| Lease Agreements One
Lessee Lease Description [Line Items]
Lessee operating lease expiry month and year		2024-09
Offices and Laboratory \| Mountain View, California \| Lease Agreements Two
Lessee Lease Description [Line Items]
Lessee operating lease expiry month and year		2025-04

Commitments and Contingencies - Schedule of ROU Assets and Related Lease Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019
Assets And Liabilities Lessee [Abstract]
Cash paid for operating lease liabilities	$ 1,527
Right-of-use asset recognized in exchange for new lease obligations	14,137
Current operating lease liabilities	2,483	$ 708
Non-current operating lease liabilities	12,244
Operating lease cost	1,396
Variable lease cost	$ 683
Weighted average remaining lease term in years	5 years 1 month 6 days
Weighted average discount rate	3.80%

Commitments and Contingencies - Schedule of Maturities of Lease Liabilities (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Operating Lease Liabilities Payments Due [Abstract]
2020	$ 3,002
2021	3,086
2022	3,172
2023	3,261
2024	3,008
Thereafter	733
Total	16,262
Less imputed interest	(1,535)
Total lease liabilities	$ 14,727

Net Loss Per Share - Summary of Potentially Dilutive Securities Not Included in the Diluted Per Share Calculations (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in diluted per share calculations	2,347,468	11,141,423
Series A Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in diluted per share calculations		401,004
Series B Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in diluted per share calculations		9,100,616
Restricted Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in diluted per share calculations	58,259	116,518
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in diluted per share calculations	2,289,209	1,523,285