Document And Entity Information - shares	9 Months Ended
Document And Entity Information - shares	Sep. 30, 2019	Nov. 01, 2019
Document And Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Registrant Name	IGM Biosciences, Inc.
Entity Central Index Key	0001496323
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
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 Quarterly Report	true
Document Transition Report	false
Common Stock
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		24,104,694
Non-voting Common Stock
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		6,431,205

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 193,679	$ 1,887
Short-term investments	48,396
Prepaid expenses and other current assets	6,005	485
Income tax receivable	35	35
Total current assets	248,115	2,407
Property and equipment, net	2,585	1,472
Long-term investments	9,274
Operating lease right-of-use asset	9,882
Restricted cash		100
Total assets	269,856	3,979
Current liabilities:
Accounts payable	2,778	164
Accrued liabilities	2,082	3,582
Lease liabilities, current	1,564
Deferred rent		108
Related party loan		5,027
Other current liabilities		9
Total current liabilities	6,424	8,890
Lease liabilities, non-current	8,810
Total liabilities	15,234	8,890
Commitments and contingencies (Note 9)
Convertible preferred stock, $0.01 par value; 0 shares authorized as of September 30, 2019 and 9,501,624 shares authorized as of December 31, 2018; 0 shares issued and outstanding as of September 30, 2019 and 9,501,620 issued and outstanding as of December 31, 2018; liquidation value of $0 as of September 30, 2019 and $61,466 as of December 31, 2018		60,917
Stockholder's (deficit) equity;
Preferred stock, $0.01 par value; 200,000,000 shares authorized as of September 30, 2019 and 0 shares authorized as of December 31, 2018; 0 shares issued and outstanding as of September 30, 2019 and December 31, 2018
Common stock, value	240	4
Additional paid-in-capital	346,679	751
Due from related party		(2,511)
Accumulated other comprehensive income	29
Accumulated deficit	(92,390)	(64,072)
Total stockholders’ equity (deficit)	254,622	(65,828)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	269,856	$ 3,979
Non-voting Common Stock
Stockholder's (deficit) equity;
Common stock, value	64
Total stockholders’ equity (deficit)	$ 64

Condensed Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Thousands	Sep. 30, 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	24,046,435	438,074
Common stock, shares outstanding	24,046,435	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

Condensed Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating expenses:
Research and development	$ 8,279	$ 5,172	$ 22,494	$ 11,148
General and administrative	2,394	1,373	6,067	2,597
Total operating expenses	10,673	6,545	28,561	13,745
Loss from operations	(10,673)	(6,545)	(28,561)	(13,745)
Other income, net	501	28	243	87
Net loss	$ (10,172)	$ (6,517)	$ (28,318)	$ (13,658)
Net loss per share, basic and diluted	$ (2.41)	$ (14.88)	$ (16.13)	$ (31.18)
Weighted-average common shares outstanding, basic and diluted	4,222,259	438,074	1,755,526	438,074

- Definition

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

+ References + Details

Condensed Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (10,172)	$ (6,517)	$ (28,318)	$ (13,658)
Other comprehensive income:
Unrealized gain on investments	29		29
Comprehensive loss	$ (10,143)	$ (6,517)	$ (28,289)	$ (13,658)

- Definition

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

+ References + Details

Condensed Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Due To (From) Related Party	IPO	Convertible Preferred Stock	Non-voting Common 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, 2017				$ 40,783
Convertible preferred stock balance, shares at Dec. 31, 2017				6,384,797
Convertible preferred stock balance at Mar. 31, 2018				$ 40,783
Convertible preferred stock balance, shares at Mar. 31, 2018				6,384,797
Balance at Dec. 31, 2017	$ (40,503)	$ (34,625)				$ 4		$ 35,479			$ (41,361)
Balance, shares at Dec. 31, 2017						438,074
Related party equity transaction	28	(387)						415
Stock-based compensation expense	22							22
Net loss	(2,926)										(2,926)
Balance at Mar. 31, 2018	(43,379)	(35,012)				$ 4		35,916			(44,287)
Balance,shares at Mar. 31, 2018						438,074
Convertible preferred stock balance at Dec. 31, 2017				$ 40,783
Convertible preferred stock balance, shares at Dec. 31, 2017				6,384,797
Convertible preferred stock balance at Sep. 30, 2018				$ 40,783
Convertible preferred stock balance, shares at Sep. 30, 2018				6,384,797
Balance at Dec. 31, 2017	(40,503)	(34,625)				$ 4		35,479			(41,361)
Balance, shares at Dec. 31, 2017						438,074
Net loss	(13,658)
Balance at Sep. 30, 2018	(42,001)	11,031				$ 4		1,983			(55,019)
Balance,shares at Sep. 30, 2018						438,074
Convertible preferred stock balance at Mar. 31, 2018				$ 40,783
Convertible preferred stock balance, shares at Mar. 31, 2018				6,384,797
Convertible preferred stock balance at Jun. 30, 2018				$ 40,783
Convertible preferred stock balance, shares at Jun. 30, 2018				6,384,797
Balance at Mar. 31, 2018	(43,379)	(35,012)				$ 4		35,916			(44,287)
Balance, shares at Mar. 31, 2018						438,074
Related party equity transaction	3,848	3,428						420
Stock-based compensation expense	22							22
Net loss	(4,215)										(4,215)
Balance at Jun. 30, 2018	(43,724)	(31,584)				$ 4		36,358			(48,502)
Balance,shares at Jun. 30, 2018						438,074
Convertible preferred stock balance at Sep. 30, 2018				$ 40,783
Convertible preferred stock balance, shares at Sep. 30, 2018				6,384,797
Related party equity transaction	8,220	42,615						(34,395)
Stock-based compensation expense	20							20
Net loss	(6,517)										(6,517)
Balance at Sep. 30, 2018	(42,001)	11,031				$ 4		1,983			(55,019)
Balance,shares at Sep. 30, 2018						438,074
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
Convertible preferred stock balance at Mar. 31, 2019				$ 60,917
Convertible preferred stock balance, shares at Mar. 31, 2019				9,501,620
Balance at Dec. 31, 2018	$ (65,828)	(2,511)				$ 4		751			(64,072)
Balance, shares at Dec. 31, 2018						438,074
Exercise of stock options	10							10
Exercise of stock options, shares						7,566
Capital contribution from related party	23							23
Stock-based compensation expense	139							139
Net loss	(7,470)										(7,470)
Balance at Mar. 31, 2019	(73,126)	(2,511)				$ 4		923			(71,542)
Balance,shares at Mar. 31, 2019						445,640
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
Convertible preferred stock balance, shares at Sep. 30, 2019	0			0
Balance at Dec. 31, 2018	$ (65,828)	(2,511)				$ 4		751			(64,072)
Balance, shares at Dec. 31, 2018						438,074
Exercise of stock options, shares	176,551
Unrealized gain on investments	$ 29
Net loss	(28,318)
Balance at Sep. 30, 2019	254,622				$ 64	$ 240		346,679		$ 29	(92,390)
Balance,shares at Sep. 30, 2019					6,431,205	24,046,435
Convertible preferred stock balance at Mar. 31, 2019				$ 60,917
Convertible preferred stock balance, shares at Mar. 31, 2019				9,501,620
Issuance of Series C convertible preferred stock, net of issuance costs				$ 61,868
Issuance of Series C convertible preferred stock, net of issuance costs, shares				4,690,997
Convertible preferred stock balance at Jun. 30, 2019				$ 122,785
Convertible preferred stock balance, shares at Jun. 30, 2019				14,192,617
Balance at Mar. 31, 2019	(73,126)	(2,511)				$ 4		923			(71,542)
Balance, shares at Mar. 31, 2019						445,640
Exercise of stock options	154					$ 2		152
Exercise of stock options, shares						165,656
Issuance of common stock	11							11
Issuance of common stock, shares						7,565
Related party equity transaction	2,527	$ 2,511						16
Stock-based compensation expense	141							141
Net loss	(10,676)										(10,676)
Balance at Jun. 30, 2019	$ (80,969)					$ 6		1,243			(82,218)
Balance,shares at Jun. 30, 2019						618,861
Issuance of Series C convertible preferred stock, net of issuance costs				$ 39,768
Issuance of Series C convertible preferred stock, net of issuance costs, shares				3,026,449
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 Sep. 30, 2019	0			0
Exercise of stock options	$ 5							5
Exercise of stock options, shares						3,329
Issuance of common stock			$ 182,842				$ 125		$ 182,717
Issuance of common stock, shares							12,578,125
Vesting of restricted stock						$ 1		(1)
Vesting of restricted stock, shares						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	29									29
Stock-based compensation expense	334							334
Net loss	(10,172)										(10,172)
Balance at Sep. 30, 2019	$ 254,622				$ 64	$ 240		$ 346,679		$ 29	$ (92,390)
Balance,shares at Sep. 30, 2019					6,431,205	24,046,435

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net loss	$ (28,318)	$ (13,658)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	416	191
Stock-based compensation expense	614	64
Net amortization of premiums and accretion of discounts on investments	(52)
Amortization of operating lease right-of-use assets	1,203
Changes in assets and liabilities:
Prepaid expenses and other current assets	(5,335)	(448)
Other assets		8
Income tax receivable		(35)
Accounts payable	655	(192)
Accrued liabilities	(1,377)	455
Income tax payable		(128)
Deferred rent		(108)
Lease liabilities	(819)
Other current liabilities	(36)	9
Other long-term liabilities		(9)
Net cash used in operating activities	(33,049)	(13,851)
Cash flows from investing activities:
Purchase of property and equipment	(1,737)	(431)
Purchases of investments	(57,774)
Net cash used in investing activities	(59,511)	(431)
Cash flows from financing activities:
Proceeds from common stock issuance	11
Proceeds from exercise of stock options	169
Proceeds from issuance of initial public offering, net of underwriters' commission	187,163
Net cash provided by financing activities	284,252	17,096
Net increase in cash, cash equivalents and restricted cash	191,692	2,814
Cash, cash equivalents, and restricted cash, beginning of period	1,987	482
Cash, cash equivalents, and restricted cash, end of period	193,679	3,296
Cash and cash equivalents	193,679	3,196
Restricted cash		100
Supplemental disclosure of cash flow information:
Cash paid for income taxes		167
Supplemental disclosure of non-cash activities:
Acquisition of property and equipment in accounts payable and accrued liabilities	84
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	(2,420)
Supplemental disclosure of non-cash activities:
Issuance costs in accounts payable and accrued liabilities	1,900
Series C Convertible Preferred Stock
Cash flows from financing activities:
Payment of issuance costs	(220)
Supplemental disclosure of non-cash activities:
Issuance costs in accounts payable and accrued liabilities	144
New Investors \| Series C Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from issuance of Series C convertible preferred stock	72,000
Haldor Topsøe Holding A/S and Holdco
Cash flows from financing activities:
Proceeds from related party capital contribution	2,549	12,096
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 activities:
Settlement of related party loan through issuance of Series C convertible preferred stock	20,000
Related party equity transaction		$ 34,625
Haldor Topsøe Holding A/S and Holdco \| Series C Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from issuance of Series C convertible preferred stock	$ 10,000

Organization

9 Months Ended

Sep. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization

Note 1. Organization

Description of the Business

IGM Biosciences, Inc. (the Company) was incorporated in the state of Delaware in August 1993 under the name Palingen, Inc. and the name was subsequently changed to IGM Biosciences, Inc. in 2010. The Company’s headquarters are in Mountain View, California. IGM Biosciences, Inc. is a biotechnology company engaged in the development of IgM antibody therapeutics for the treatment of cancer.

In December 2017, the Company established a holding company (Holdco); in April 2019, Holdco was subsequently dissolved and equity interests in Holdco were converted into equity interests in the Company. The information included in these financial statements is consistently presented as if it is that of the Company, even during the interim period when investors held their equity interests in Holdco. For the period ended December 31, 2018, Haldor Topsøe Holding A/S was the majority investor in the Company either through its direct equity ownership or indirectly as the majority owner of Holdco. Haldor Topsøe Holding A/S and Holdco represent a combined entity (Majority Investor) as referenced herein.

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 condensed 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

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

The Company has incurred net operating losses and negative cash flows from operations since its inception and had an accumulated deficit of $92.4 million at September 30, 2019. As of September 30, 2019, the Company had cash, cash equivalents and investments of $251.3 million. 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.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Note 2. Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited condensed financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (GAAP) and applicable rules and regulations of the Securities and Exchange Commission (SEC) regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP have been condensed or omitted, and accordingly the balance sheet as of December 31, 2018 has been derived from the audited financial statements at that date but does not include all of the information required by GAAP for complete financial statements. These unaudited interim condensed financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair statement of the Company’s financial information. The results of operations for the three and nine months ended September 30, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or for any other interim period or for any other future year.

The accompanying interim unaudited condensed financial statements should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2018, which are included in the Company’s prospectus related to the Company’s IPO, filed with the SEC on September 18, 2019, pursuant to Rule 424(b) under the Securities Act of 1933.

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.

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, cash equivalents and investments. The Company invests in money market funds, U.S. Treasury 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 condensed 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, cash equivalents 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, including those more fully described in the “Risk Factors” section of this Quarterly Report on Form 10-Q.

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, 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 condensed 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.

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.

The Company makes significant judgments and estimates in determining the accrual balance in each reporting period. 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 our 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 September 30, 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 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.

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 the three months ended September 30, 2019, the Company elected to early adopt Accounting Standard Update (ASU) No. 2016-02, Leases (Topic 842) and its associated amendments (ASC 842) 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 contains a bargain purchase option, (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 September 30, 2019, the Company's lease population consisted of real estate. As of the date of adoption of ASC 842 and September 30, 2019, the Company did not have finance leases.

Operating leases are included in operating lease right-of-use assets, current operating lease liabilities, and non-current operating lease liabilities in the Company’s condensed 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 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 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 condensed balance sheet. For more information about the impact of adoption and disclosures on the Company’s leases, refer to “Note 9 – Commitments and Contingencies.”

Recently Adopted Accounting Standards

During the three months ended September 30, 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 the standard, 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 9 – Commitments and Contingencies.”

Recent Accounting Pronouncements

In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (ASU 2016-13), 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. ASU 2016-13 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. ASU 2016-13 is effective for fiscal years beginning after December 15, 2019 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 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 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.

Fair Value Measurement

9 Months Ended

Sep. 30, 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 September 30, 2019, investments measured and recognized at fair value are as follows (in thousands):

		September 30, 2019
	Fair Value Hierarchy Level	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Investments
U.S. Treasury securities	Level 1	$	29,191	$	28	$	—	$	29,219
Corporate bond	Level 2		8,634		1		—		8,635
Commercial paper	Level 2		19,816		—		—		19,816
Total		$	57,641	$	29	$	—	$	57,670

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 September 30, 2019 (in thousands):

	September 30, 2019
Due in less than one year	$	48,396
Due in more than one year		9,274
Total	$	57,670

- 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

Balance Sheet Components

9 Months Ended

Sep. 30, 2019

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components

Note 4. Balance Sheet Components

Property and Equipment, Net

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

	September 30,			December 31,
	2019			2018
Laboratory equipment	$	3,127		$	1,987
Office equipment		150			127
Leasehold improvement		71			25
Construction in progress		320			—
Total property and equipment, gross		3,668			2,139
Less: Accumulated depreciation		(1,083	)		(667	)
Total property and equipment, net	$	2,585		$	1,472

Depreciation expense was approximately $0.2 million and $0.1 million for the three months ended September 30, 2019 and 2018, respectively. Depreciation expense was approximately $0.4 million and $0.2 million for the nine months ended September 30, 2019 and 2018, respectively.

Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	September 30,		December 31,
	2019		2018
Accrued research and development materials and services	$	376	$	2,395
Accrued professional services		226		563
Accrued compensation		1,319		177
Other		161		447
Total accrued liabilities	$	2,082	$	3,582

Common Stock and Non-Voting Common Stock

9 Months Ended

Sep. 30, 2019

Stockholders Equity Note [Abstract]

Common Stock and Non-Voting Common Stock

Note 5. Common Stock and Non-Voting Common Stock

As of September 30, 2019 and December 31, 2018, the Company’s certificate of incorporation authorized the Company to issue 1,006,431,208 shares of common stock (including 6,431,208 shares of non-voting common stock) and 200,000,000 shares of preferred stock, respectively, at a par value of $0.01 per share. Each share of common stock is entitled to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when declared by the Company’s Board of Directors, subject to prior rights of the preferred stockholders. As of September 30, 2019 and December 31, 2018, no dividends have been declared to date.

The Company had reserved common stock, on an as-converted basis, for future issuance as follows:

	September 30,		December 31,
	2019		2018
Preferred stock, issued and outstanding		—		9,501,620
Restricted stock, issued and outstanding		58,259		116,518
Stock options, issued and outstanding		2,264,937		1,523,285
Stock options, future issuance		2,703,702		456,818
Employee stock purchase plan, available for future grants		280,000		—
Total		5,306,898		11,598,241

Convertible Preferred Stock

9 Months Ended

Sep. 30, 2019

Temporary Equity Disclosure [Abstract]

Convertible Preferred Stock

Note 6. 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 the nine months ended September 30, 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 September 30, 2019.

Stock-Based Compensation

9 Months Ended

Sep. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 7. 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 (RSUs), 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 September 30, 2019, 2,703,702 shares of common stock remained available for issuance under 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 September 30, 2019, 280,000 shares of common stock remained available for issuance under 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 condensed statements of operations and allocated as follows (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2019		2018		2019		2018
Research and development	$	116	$	9	$	330	$	26
General and administrative		218		12		284		38
Total stock-based compensation expense	$	334	$	21	$	614	$	64

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)
Balance—December 31, 2018		456,818			1,523,285
Addition - Option pool		3,165,087			—
Granted		(929,561	)		929,561		$	5.63
Exercised		—			(176,551	)		0.96
Cancelled		11,358			(11,358	)		1.08
Balance—September 30, 2019		2,703,702			2,264,937		$	3.01		8.3
Exercisable – September 30, 2019					841,852			1.31		6.4

There were no options granted during the three and nine months ended September 30, 2018. The fair value of employee stock options was estimated using the following weighted-average assumptions:

	Three Months Ended					Nine Months Ended
	September 30,					September 30,
	2019			2018		2019			2018
Expected term in years		6.0			—		6.0			—
Expected volatility		79.4	%		—		79.3	%		—
Risk-free interest rate		1.6	%		—		2.2	%		—
Dividend yield		—			—		—			—
Weighted average fair value of share-based awards granted	$	8.8			—	$	3.9			—

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

	Three Months Ended					Nine Months Ended
	September 30,					September 30,
	2019			2018		2019			2018
Expected term in years		0.7			—		0.7			—
Expected volatility		74.3	%		—		74.3	%		—
Risk-free interest rate		1.9	%		—		1.9	%		—
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 September 30, 2019, 58,259 shares of restricted stock were vested. For the three and nine months ended September 30, 2019, the related stock-based compensation was immaterial. As of September 30, 2019, there was $0.1 million of unrecognized stock-based compensation related to restricted stock, which the Company expects to recognize over a remaining weighted-average period of 0.8 years.

Net Loss Per Share Attributable to Common Stockholders

9 Months Ended

Sep. 30, 2019

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stockholders

Note 8. Net Loss Per Share Attributable to Common Stockholders

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

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2019			2018			2019			2018
Numerator:
Net loss	$	(10,172	)	$	(6,517	)	$	(28,318	)	$	(13,658	)
Denominator:
Weighted average common shares outstanding used to compute net loss per share, basic and diluted		4,222,259			438,074			1,755,526			438,074
Net loss per share attributable to common stockholders	$	(2.41	)	$	(14.88	)	$	(16.13	)	$	(31.18	)

Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share for all periods as the inclusion of all common stock equivalents outstanding would have been anti-dilutive. Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:

	September 30,
	2019		2018
Series A convertible preferred stock		—		401,004
Series B convertible preferred stock		—		5,983,793
Restricted stock		58,259		—
Stock options		2,264,937		768,762
Total		2,323,196		7,153,559

Commitments and Contingencies

9 Months Ended

Sep. 30, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 9. Commitments and Contingencies

Operating Leases

The Company leases its headquarters with its main offices and laboratory facilities in Mountain View, California under a lease agreement that ends in April 2025.

During the three months ended September 30, 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 adoption of ASC 842 resulted in an increase to total assets and liabilities due to the recording of operating lease ROU assets and operating lease liabilities of approximately $0.6 million and $0.7 million, respectively, as of January 1, 2019. ROU assets and lease liabilities are recognized based on the present value of the fixed and in-substance fixed lease payments over the lease term at the commencement date. The ROU assets also include any initial direct costs incurred and lease payments made at or before the commencement date and are reduced by lease incentives. Variable lease costs represent payments that are dependent on usage, a rate or index. Variable lease cost primarily relates to common area maintenance charges for its real estate leases as the Company elected not to separate non-lease components from lease components upon adoption of ASC 842. 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 10 - Related Party Transactions with its Majority Investor,” the Company entered into an agreement with the Majority Investor in February 2019 whereby the Majority Investor lent its credit and worthiness to the Company. 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 Majority Investor’s credit rating.

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

	September 30, 2019
Cash paid for operating lease liabilities	$	983
Right-of-use assets recognized in exchange for new lease obligations		9,882
Current operating lease liabilities		1,564
Non-current operating lease liabilities		8,810
Weighted average remaining lease term		5.6
Weighted average discount rate		3.5	%

Maturities of lease liabilities as of September 30, 2019 were as follows (in thousands):

	Operating
	Lease
Year Ending December	Commitments
2019 (remaining three months)	$	455
2020		1,935
2021		1,993
2022		2,053
2023		2,115
2024		2,178
Thereafter		734
Total		11,463
Less imputed interest		(1,089	)
Total lease liabilities	$	10,374

Rent expense for three and nine months ended September 30, 2019 was $0.7 million and $1.4 million, respectively, which includes additional rent charges for common area maintenance.

Rent expense for the three and nine months ended September 30, 2018 was $0.2 million and $0.5 million, respectively. Future minimum lease payments as of December 31, 2018 are $0.7 million in 2019.

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 nine months ended September 30, 2019 and, to the best of its knowledge, no material legal proceedings are currently pending or threatened.

Indemnification

The Company enters into standard indemnification arrangements in the ordinary course of business. Pursuant to these arrangements, the Company indemnifies, holds harmless and agrees to reimburse the indemnified parties for losses suffered or incurred by the indemnified party, in connection with any trade secret, copyright, patent or other intellectual property infringement claim by any third party with respect to its technology. The term of these indemnification agreements is generally perpetual any time after the execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these arrangements is not determinable. The Company has never incurred costs to defend lawsuits or settle claims related to these indemnification agreements. As a result, the Company believes the fair value of these agreements is not material.

Related Party Transactions with its Majority Investor

9 Months Ended

Sep. 30, 2019

Note 10. Related Party Transactions with its Majority Investor

The following are transactions that occurred between the Company and the Majority Investor, as defined in Note 1.

Lease Guarantee

In February 2019, the Majority Investor entered into an agreement to lend its credit and creditworthiness to the Company by providing a guarantee to allow the Company to enter into the lease agreement for its facilities in Mountain View, California. The Company has not drawn on the guarantee nor incurred any related commission expense through September 30, 2019.

Settlement of Related Party Receivable

In April 2019, the Company received $2.5 million in cash from the Majority Investor in settlement of the outstanding note receivable as of December 31, 2018.

Related Party Loan

In January, February and April 2019, the Company issued an unsecured promissory note to the Majority Investor for proceeds of $15.0 million. In June 2019, the outstanding unsecured promissory note, amounting to $20.0 million, issued by the Majority Investor was settled as shares of Series C convertible preferred stock (see below). During the three and nine months ended September 30, 2019, the Company paid $0.3 million in interest related to the unsecured promissory note issued to the Majority Investor.

2019 Series C Issuance

In June 2019, the Company issued 2,269,838 shares of Series C convertible preferred stock to the Majority Investor for $30.0 million. A portion of the shares of Series C convertible preferred stock was issued to satisfy the settlement of the unsecured promissory note amounting to $20.0 million issued by the Majority Investor.

Initial Public Offering

Immediately prior to the closing of the IPO, all outstanding shares of the Company’s convertible preferred stock held by the Majority Investor automatically converted into common stock and non-voting common stock. The Majority Investor also purchased an additional 1,250,000 shares of common stock in connection with the IPO. As a result of these two events, the Majority Investor owned 10,289,453 shares of common stock and 2,269,838 shares of non-voting common stock, upon closing of the IPO.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2019
Accounting Policies [Abstract]
Description of the Business	Description of the Business IGM Biosciences, Inc. (the Company) was incorporated in the state of Delaware in August 1993 under the name Palingen, Inc. and the name was subsequently changed to IGM Biosciences, Inc. in 2010. The Company’s headquarters are in Mountain View, California. IGM Biosciences, Inc. is a biotechnology company engaged in the development of IgM antibody therapeutics for the treatment of cancer. In December 2017, the Company established a holding company (Holdco); in April 2019, Holdco was subsequently dissolved and equity interests in Holdco were converted into equity interests in the Company. The information included in these financial statements is consistently presented as if it is that of the Company, even during the interim period when investors held their equity interests in Holdco. For the period ended December 31, 2018, Haldor Topsøe Holding A/S was the majority investor in the Company either through its direct equity ownership or indirectly as the majority owner of Holdco. Haldor Topsøe Holding A/S and Holdco represent a combined entity (Majority Investor) as referenced herein.
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 condensed 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 $92.4 million at September 30, 2019. As of September 30, 2019, the Company had cash, cash equivalents and investments of $251.3 million. 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.
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (GAAP) and applicable rules and regulations of the Securities and Exchange Commission (SEC) regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP have been condensed or omitted, and accordingly the balance sheet as of December 31, 2018 has been derived from the audited financial statements at that date but does not include all of the information required by GAAP for complete financial statements. These unaudited interim condensed financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair statement of the Company’s financial information. The results of operations for the three and nine months ended September 30, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or for any other interim period or for any other future year. The accompanying interim unaudited condensed financial statements should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2018, which are included in the Company’s prospectus related to the Company’s IPO, filed with the SEC on September 18, 2019, pursuant to Rule 424(b) under the Securities Act of 1933.
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.
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, cash equivalents and investments. The Company invests in money market funds, U.S. Treasury 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 condensed 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, cash equivalents 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, including those more fully described in the “Risk Factors” section of this Quarterly Report on Form 10-Q. 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, 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 condensed 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.
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. The Company makes significant judgments and estimates in determining the accrual balance in each reporting period. 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 our 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 September 30, 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 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.
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 the three months ended September 30, 2019, the Company elected to early adopt Accounting Standard Update (ASU) No. 2016-02, Leases (Topic 842) and its associated amendments (ASC 842) 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 contains a bargain purchase option, (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 September 30, 2019, the Company's lease population consisted of real estate. As of the date of adoption of ASC 842 and September 30, 2019, the Company did not have finance leases. Operating leases are included in operating lease right-of-use assets, current operating lease liabilities, and non-current operating lease liabilities in the Company’s condensed 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 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 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 condensed balance sheet. For more information about the impact of adoption and disclosures on the Company’s leases, refer to “Note 9 – Commitments and Contingencies.”
Recently Adopted Accounting Standards and Accounting Pronouncements	Recently Adopted Accounting Standards During the three months ended September 30, 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 the standard, 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 9 – Commitments and Contingencies.” Recent Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (ASU 2016-13), 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. ASU 2016-13 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. ASU 2016-13 is effective for fiscal years beginning after December 15, 2019 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 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 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.

Fair Value Measurement (Tables)

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [Abstract]

Summary of Investments Measured and Recognized at Fair Value

As of September 30, 2019, investments measured and recognized at fair value are as follows (in thousands):

		September 30, 2019
	Fair Value Hierarchy Level	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Investments
U.S. Treasury securities	Level 1	$	29,191	$	28	$	—	$	29,219
Corporate bond	Level 2		8,634		1		—		8,635
Commercial paper	Level 2		19,816		—		—		19,816
Total		$	57,641	$	29	$	—	$	57,670

Summary of Contractual Maturities of Investments

The following table presents the contractual maturities of the Company’s investments as of September 30, 2019 (in thousands):

	September 30, 2019
Due in less than one year	$	48,396
Due in more than one year		9,274
Total	$	57,670

Balance Sheet Components (Tables)

9 Months Ended

Sep. 30, 2019

Balance Sheet Related Disclosures [Abstract]

Schedule of Property and Equipment, Net

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

	September 30,			December 31,
	2019			2018
Laboratory equipment	$	3,127		$	1,987
Office equipment		150			127
Leasehold improvement		71			25
Construction in progress		320			—
Total property and equipment, gross		3,668			2,139
Less: Accumulated depreciation		(1,083	)		(667	)
Total property and equipment, net	$	2,585		$	1,472

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	September 30,		December 31,
	2019		2018
Accrued research and development materials and services	$	376	$	2,395
Accrued professional services		226		563
Accrued compensation		1,319		177
Other		161		447
Total accrued liabilities	$	2,082	$	3,582

Common Stock and Non-Voting Common Stock (Tables)

9 Months Ended

Sep. 30, 2019

Stockholders Equity Note [Abstract]

Schedule of Number of Common Stock Reserved for Future Issuance

The Company had reserved common stock, on an as-converted basis, for future issuance as follows:

	September 30,		December 31,
	2019		2018
Preferred stock, issued and outstanding		—		9,501,620
Restricted stock, issued and outstanding		58,259		116,518
Stock options, issued and outstanding		2,264,937		1,523,285
Stock options, future issuance		2,703,702		456,818
Employee stock purchase plan, available for future grants		280,000		—
Total		5,306,898		11,598,241

Convertible Preferred Stock (Tables)

9 Months Ended

Sep. 30, 2019

Temporary Equity Disclosure [Abstract]

Schedule of Issued and Outstanding Convertible Preferred Stock and Its Principal Terms

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

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 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 condensed statements of operations and allocated as follows (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2019		2018		2019		2018
Research and development	$	116	$	9	$	330	$	26
General and administrative		218		12		284		38
Total stock-based compensation expense	$	334	$	21	$	614	$	64

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)
Balance—December 31, 2018		456,818			1,523,285
Addition - Option pool		3,165,087			—
Granted		(929,561	)		929,561		$	5.63
Exercised		—			(176,551	)		0.96
Cancelled		11,358			(11,358	)		1.08
Balance—September 30, 2019		2,703,702			2,264,937		$	3.01		8.3
Exercisable – September 30, 2019					841,852			1.31		6.4

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:

	Three Months Ended					Nine Months Ended
	September 30,					September 30,
	2019			2018		2019			2018
Expected term in years		6.0			—		6.0			—
Expected volatility		79.4	%		—		79.3	%		—
Risk-free interest rate		1.6	%		—		2.2	%		—
Dividend yield		—			—		—			—
Weighted average fair value of share-based awards granted	$	8.8			—	$	3.9			—

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:

	Three Months Ended					Nine Months Ended
	September 30,					September 30,
	2019			2018		2019			2018
Expected term in years		0.7			—		0.7			—
Expected volatility		74.3	%		—		74.3	%		—
Risk-free interest rate		1.9	%		—		1.9	%		—
Dividend yield		—			—		—			—

Net Loss Per Share Attributable to Common Stockholders (Tables)

9 Months Ended

Sep. 30, 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):

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2019			2018			2019			2018
Numerator:
Net loss	$	(10,172	)	$	(6,517	)	$	(28,318	)	$	(13,658	)
Denominator:
Weighted average common shares outstanding used to compute net loss per share, basic and diluted		4,222,259			438,074			1,755,526			438,074
Net loss per share attributable to common stockholders	$	(2.41	)	$	(14.88	)	$	(16.13	)	$	(31.18	)

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:

	September 30,
	2019		2018
Series A convertible preferred stock		—		401,004
Series B convertible preferred stock		—		5,983,793
Restricted stock		58,259		—
Stock options		2,264,937		768,762
Total		2,323,196		7,153,559

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2019

Commitments And Contingencies Disclosure [Abstract]

Schedule of ROU Assets and Related Lease Liabilities

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

	September 30, 2019
Cash paid for operating lease liabilities	$	983
Right-of-use assets recognized in exchange for new lease obligations		9,882
Current operating lease liabilities		1,564
Non-current operating lease liabilities		8,810
Weighted average remaining lease term		5.6
Weighted average discount rate		3.5	%

Schedule of Maturities of Lease Liabilities

Maturities of lease liabilities as of September 30, 2019 were as follows (in thousands):

	Operating
	Lease
Year Ending December	Commitments
2019 (remaining three months)	$	455
2020		1,935
2021		1,993
2022		2,053
2023		2,115
2024		2,178
Thereafter		734
Total		11,463
Less imputed interest		(1,089	)
Total lease liabilities	$	10,374

Organization - Additional Information (Details) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 20, 2019 $ / shares shares	Sep. 19, 2019 USD ($) shares	Aug. 31, 2019	Sep. 30, 2019 USD ($) shares	Jun. 30, 2019 shares	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
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 \| $						$ 187,163
Accumulated deficit \| $				$ 92,390		92,390	$ 64,072
Cash, cash equivalents and investments \| $				$ 251,300		$ 251,300
Common Stock
Subsidiary Sale Of Stock [Line Items]
Common stock, shares issued					7,565
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 \| 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
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
Non-voting Common Stock \| IPO
Subsidiary Sale Of Stock [Line Items]
Conversion of convertible preferred stock into common stock, shares		6,431,205

Fair Value Measurement - Summary of Investments Measured and Recognized at Fair Value (Details) - Fair Value, Recurring - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 57,641,000
Gross Unrealized Gains	29,000
Fair Value	57,670,000	$ 0
U.S. Treasury Securities \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	29,191,000
Gross Unrealized Gains	28,000
Fair Value	29,219,000
Corporate Bond \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	8,634,000
Gross Unrealized Gains	1,000
Fair Value	8,635,000
Commercial Paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	19,816,000
Fair Value	$ 19,816,000

Fair Value Measurement - Summary of Contractual Maturities of Investments (Details) - Fair Value, Recurring - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Due in less than one year	$ 48,396,000
Due in more than one year	9,274,000
Total	$ 57,670,000	$ 0

Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 3,668	$ 2,139
Less: Accumulated depreciation	(1,083)	(667)
Total property and equipment, net	2,585	1,472
Laboratory Equipment
Property Plant And Equipment [Line Items]
Total property and equipment, gross	3,127	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	71	$ 25
Construction In Progress
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 320

Balance Sheet Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Accrued research and development materials and services	$ 376	$ 2,395
Accrued professional services	226	563
Accrued compensation	1,319	177
Other	161	447
Total accrued liabilities	$ 2,082	$ 3,582

Common Stock and Non-Voting Common Stock - Additional Information (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) Vote $ / shares shares	Dec. 31, 2018 USD ($) $ / 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	$ 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	Sep. 30, 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	2,264,937	1,523,285
Stock options, future issuance	2,703,702	456,818
Employee stock purchase plan, available for future grants	280,000
Total	5,306,898	11,598,241

Convertible Preferred Stock - Schedule of Issued and Outstanding Convertible Preferred Stock and its Principal Terms (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized	0	9,501,624
Convertible Preferred Stock, Shares Issued and Outstanding		9,501,620
Convertible Preferred Stock, Carrying Value		$ 60,917
Convertible Preferred Stock, Aggregate Liquidation Preference	$ 0	$ 61,466
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		401,004
Convertible Preferred Stock, Shares Issued and Outstanding		401,004
Convertible Preferred Stock, Original Issue Price		$ 3.3042
Convertible Preferred Stock, Carrying Value		$ 1,325
Convertible Preferred Stock, Aggregate Liquidation Preference		$ 1,325
Series B Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		9,100,620
Convertible Preferred Stock, Shares Issued and Outstanding		9,100,616
Convertible Preferred Stock, Original Issue Price		$ 6.6084
Convertible Preferred Stock, Carrying Value		$ 59,592
Convertible Preferred Stock, Aggregate Liquidation Preference		$ 60,141

Convertible Preferred Stock - Additional Information (Details) - USD ($) $ in Millions		3 Months Ended
	Sep. 19, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Temporary Equity [Line Items]
Convertible preferred stock, shares outstanding		0			9,501,620
Common Stock
Temporary Equity [Line Items]
Conversion of convertible preferred stock into common stock, shares	10,787,861	10,787,861
Series C Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock shares issued	7,717,446
Proceeds from issuance of preferred stock	$ 102.0
Debt settled	$ 20.0
Non-voting Common Stock
Temporary Equity [Line Items]
Conversion of convertible preferred stock into common stock, shares	6,431,205	6,431,205
Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock shares issued		3,026,449	4,690,997
Convertible preferred stock, shares outstanding		0	14,192,617	9,501,620	9,501,620	6,384,797	6,384,797	6,384,797	6,384,797
IPO \| Common Stock
Temporary Equity [Line Items]
Conversion of convertible preferred stock into common stock, shares	10,787,861
IPO \| Non-voting Common Stock
Temporary Equity [Line Items]
Conversion of convertible preferred stock into common stock, shares	6,431,205

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance	11,598,241		5,306,898
Shares available for issuance	456,818		2,703,702
Number of stock options granted		0	929,561	0
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation			$ 0.1
Expects to recognize over a remaining weighted-average period			9 months 18 days
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			2,703,702
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 \| 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) - $ / shares	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 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		(929,561)
Outstanding Options, Shares Available for Grant, Cancelled		11,358
Outstanding Options, Shares Available for Grant, Ending balance		2,703,702
Outstanding Options, Shares, Beginning balance		1,523,285
Outstanding Options, Shares, Granted	0	929,561	0
Outstanding Options, Shares, Exercised		(176,551)
Outstanding Options, Shares, Cancelled		(11,358)
Outstanding Options, Shares, Ending balance		2,264,937
Outstanding Options, Shares, Exercisable		841,852
Outstanding Options, Weighted-Average Exercise Price, Granted		$ 5.63
Outstanding Options, Weighted-Average Exercise Price, Exercised		0.96
Outstanding Options, Weighted-Average Exercise Price, Canceled		1.08
Outstanding Options, Weighted-Average Exercise Price, Ending balance		3.01
Outstanding Options, Weighted-Average Exercise Price, Exercisable		$ 1.31
Outstanding Options, Weighted Average Remaining Contractual Term (Years)		8 years 3 months 18 days
Outstanding Options, Weighted Average Remaining Contractual Term (Years), Exercisable		6 years 4 months 24 days

Stock-Based Compensation - Summary of Fair Value of Employee Stock Options Estimated Weighted-average Assumptions (Details) - Stock Options - $ / shares	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term in years	6 years	6 years
Expected volatility	79.40%	79.30%
Risk-free interest rate	1.60%	2.20%
Weighted average fair value of share-based awards granted	$ 8.8	$ 3.9

Stock-Based Compensation - Summary of Fair Value of Employee Stock Purchase Plan Estimated Weighted-average Assumptions (Details) - Employee Stock Purchase Plan	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term in years	8 months 12 days	8 months 12 days
Expected volatility	74.30%	74.30%
Risk-free interest rate	1.90%	1.90%

Net Loss Per Share Attributable to Common Stockholders - Schedule of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net loss	$ (10,172)	$ (10,676)	$ (7,470)	$ (6,517)	$ (4,215)	$ (2,926)	$ (28,318)	$ (13,658)
Denominator:
Weighted average common shares outstanding used to compute net loss per share, basic and diluted	4,222,259			438,074			1,755,526	438,074
Net loss per share attributable to common stockholders	$ (2.41)			$ (14.88)			$ (16.13)	$ (31.18)

- Definition

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

+ References + Details

Net Loss Per Share Attributable to Common Stockholders - Summary of Potentially Dilutive Securities Not Included in the Diluted Per Share Calculations (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in diluted per share calculations	2,323,196	7,153,559
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		5,983,793
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
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in diluted per share calculations	2,264,937	768,762

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Lessee Lease Description [Line Items]
Operating lease ROU assets	$ 9,882		$ 9,882		$ 600
Operating lease liabilities	10,374		10,374		$ 700
Operating lease rent expense	$ 700	$ 200	$ 1,400	$ 500
Operating lease future minimum payments in 2019						$ 700
Offices and Laboratory \| Mountain View, California
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) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Assets And Liabilities Lessee [Abstract]
Cash paid for operating lease liabilities	$ 983
Right-of-use assets recognized in exchange for new lease obligations	9,882
Current operating lease liabilities	1,564
Non-current operating lease liabilities	$ 8,810
Weighted average remaining lease term	5 years 7 months 6 days
Weighted average discount rate	3.50%

Commitments and Contingencies - Schedule of Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019
Operating Lease Liabilities Payments Due [Abstract]
2019 (remaining three months)	$ 455
2020	1,935
2021	1,993
2022	2,053
2023	2,115
2024	2,178
Thereafter	734
Total	11,463
Less imputed interest	(1,089)
Operating lease liabilities	$ 10,374	$ 700

Related Party Transactions with its Majority Investor - Additional Information (Details) - USD ($)			1 Months Ended		3 Months Ended		4 Months Ended	9 Months Ended
	Sep. 20, 2019	Sep. 19, 2019	Jun. 30, 2019	Apr. 30, 2019	Sep. 30, 2019	Jun. 30, 2019	Apr. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
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						7,565
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
Proceeds from loan from related party								$ 15,000,000	$ 5,000,000
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			$ 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			$ 20,000,000
Interest paid					$ 300,000			$ 300,000

Condensed Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2019	Jun. 30, 2019
IPO
Stock issuance cost	$ 4.3
Series C Convertible Preferred Stock
Stock issuance cost	$ 0.3	$ 0.1

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
IPO
Summary Of Significant Accounting Policies [Line Items]
Deferred offering costs	$ 4,300,000	$ 0

Fair Value Measurement - Additional Information (Details) - USD ($)	Sep. 30, 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	$ 57,670,000	$ 0