Avidity Biosciences (RNA) 10-Q 10 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 20, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Registrant Name	Avidity Biosciences, Inc.
Entity Central Index Key	0001599901
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		37,526,631
Entity File Number	001-39321
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-1336960
Entity Address, Address Line One	10975 N. Torrey Pines Road
Entity Address, Address Line Two	Suite 150
Entity Address, City or Town	La Jolla
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92037
City Area Code	858
Local Phone Number	401-7900
Title of 12(b) Security	Common Stock, $0.0001 par value
Trading Symbol	RNA
Security Exchange Name	NASDAQ
Document Quarterly Report	true
Document Transition Report	false

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 341,142	$ 94,578
Prepaid and other assets	3,155	1,098
Total current assets	344,297	95,676
Property and equipment, net	1,295	631
Restricted cash	124	0
Other assets	417	600
Total assets	346,133	96,907
Current liabilities:
Accounts payable and accrued liabilities	6,328	2,308
Accrued compensation	2,132	1,314
Deferred revenue, current portion	5,220	3,840
Long-term debt, current portion	0	2,774
Total current liabilities	13,680	10,236
Lease liabilities, net of current portion	689	393
Deferred revenue, net of current portion	11,600	15,100
Long-term debt, net of current portion	0	1,770
Other long-term liabilities	0	45
Total liabilities	25,969	27,544
Commitments and contingencies (Note 7)	0	0
Convertible preferred stock, $0.0001 par value; authorized shares - none and 38,055 at September 30, 2020 and December 31, 2019, respectively; issued and outstanding – none and 37,267 at September 30, 2020 and December 31, 2019, respectively	0	134,720
Stockholders’ equity (deficit):
Preferred stock, $0.0001 par value, authorized shares – 40,000 and none at September 30, 2020 and December 31, 2019, respectively; issued and outstanding shares – none	0	0
Common stock, $0.0001 par value; authorized shares – 400,000 and 52,042 at September 30, 2020 and December 31, 2019, respectively; issued and outstanding shares – 37,527 and 2,989 at September 30, 2020 and December 31, 2019, respectively	4	0
Additional paid-in capital	370,425	(43,172)
Accumulated deficit	(50,265)	(22,185)
Total stockholders’ equity (deficit)	320,164	(65,357)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 346,133	$ 96,907

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.0001	$ 0.0001
Convertible preferred stock, authorized	0	38,055,000
Convertible preferred stock, issued	0	37,267,000
Convertible preferred stock, outstanding	0	37,267,000
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	40,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	400,000,000	52,042,000
Common stock, shares issued	37,527,000	2,989,000
Common stock, shares outstanding	37,527,000	2,989,000

Condensed Statements of Operati

Condensed Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Collaboration revenue	$ 1,746	$ 650	$ 4,645	$ 874
Revenue from Contract with Customer, Product and Service [Extensible List]	rna:CollaborationRevenueMember	rna:CollaborationRevenueMember	rna:CollaborationRevenueMember	rna:CollaborationRevenueMember
Operating expenses:
Research and development	$ 9,455	$ 5,099	$ 23,983	$ 8,894
General and administrative	3,757	757	8,646	3,265
Total operating expenses	13,212	5,856	32,629	12,159
Loss from operations	(11,466)	(5,206)	(27,984)	(11,285)
Other income (expense):
Interest income	27	0	188	0
Interest and other expense	0	(1,462)	(209)	(3,049)
Change in fair value of preferred warrant liability	0	0	(75)	1
Total other income (expense)	27	(1,462)	(96)	(3,048)
Net loss	$ (11,439)	$ (6,668)	$ (28,080)	$ (14,333)
Net loss per share, basic and diluted	$ (0.31)	$ (2.43)	$ (1.72)	$ (5.32)
Weighted-average shares outstanding, basic and diluted	37,420	2,739	16,361	2,692

Condensed Statements of Convert

Condensed Statements of Convertible Preferred Stock/Units and Stockholders'/Members' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	Preferred Units	Common Units	Predecessor's Deficit	Convertible Preferred Stock	Common Stock	Common StockIPO	Additional Paid-in Capital	Additional Paid-in CapitalIPO	Accumulated Deficit	Accumulated DeficitIPO
Balance at Dec. 31, 2018	$ (41,129)				$ (41,555)		$ 0		$ 0		$ 0
Preferred Units, balance, Units at Dec. 31, 2018			12,459,000
Preferred Units, balance at Dec. 31, 2018			$ 32,693
Temporary equity, balance, Shares at Dec. 31, 2018						0
Temporary equity, balance at Dec. 31, 2018						$ 0
Members' equity, balance, Units at Dec. 31, 2018				2,842,000
Members' equity, balance at Dec. 31, 2018				$ 426
Balance, Shares at Dec. 31, 2018							0
Distribution to members			(106)
Issuance of common units upon exercise of unit options	39		0	$ 39	0	0	$ 0		0		0
Issuance of common units upon exercise of unit options, Units				78,000
Vesting of early exercise options	5		0	$ 5	0	0	0		0		0
Stock-based compensation	17			17	0		0		0		0
Net loss	(2,549)		$ 0	$ 0	(2,549)	$ 0	0		0		0
Balance at Mar. 31, 2019	(43,617)				(44,104)		$ 0		0		0
Preferred Units, balance, Units at Mar. 31, 2019			12,459,000
Preferred Units, balance at Mar. 31, 2019			$ 32,587
Temporary equity, balance, Shares at Mar. 31, 2019						0
Temporary equity, balance at Mar. 31, 2019						$ 0
Members' equity, balance, Units at Mar. 31, 2019				2,920,000
Members' equity, balance at Mar. 31, 2019				$ 487
Balance, Shares at Mar. 31, 2019							0
Balance at Dec. 31, 2018	(41,129)				(41,555)		$ 0		0		0
Preferred Units, balance, Units at Dec. 31, 2018			12,459,000
Preferred Units, balance at Dec. 31, 2018			$ 32,693
Temporary equity, balance, Shares at Dec. 31, 2018						0
Temporary equity, balance at Dec. 31, 2018						$ 0
Members' equity, balance, Units at Dec. 31, 2018				2,842,000
Members' equity, balance at Dec. 31, 2018				$ 426
Balance, Shares at Dec. 31, 2018							0
Reclassification of warrant liability to equity due to adjustment from preferred stock warrant to common stock warrant upon completion of initial public offering	0
Net loss	(14,333)
Balance at Sep. 30, 2019	(55,326)				0		$ 0		(43,542)		(11,784)
Preferred Units, balance, Units at Sep. 30, 2019			0
Preferred Units, balance at Sep. 30, 2019			$ 0
Temporary equity, balance, Shares at Sep. 30, 2019						12,459,000
Temporary equity, balance at Sep. 30, 2019						$ 32,587
Members' equity, balance, Units at Sep. 30, 2019				0
Members' equity, balance at Sep. 30, 2019				$ 0
Balance, Shares at Sep. 30, 2019							2,975,000
Balance at Mar. 31, 2019	(43,617)				(44,104)		$ 0		0		0
Preferred Units, balance, Units at Mar. 31, 2019			12,459,000
Preferred Units, balance at Mar. 31, 2019			$ 32,587
Temporary equity, balance, Shares at Mar. 31, 2019						0
Temporary equity, balance at Mar. 31, 2019						$ 0
Members' equity, balance, Units at Mar. 31, 2019				2,920,000
Members' equity, balance at Mar. 31, 2019				$ 487
Balance, Shares at Mar. 31, 2019							0
Conversion from LLC to C corporation	0			$ (487)	44,104		$ 0		(43,617)		0
Conversion from LLC to C corporation, Temporary equity, Shares			(12,459,000)			12,459,000
Conversion from LLC to C corporation, Temporary equity			$ (32,587)			$ 32,587
Conversion from LLC to C corporation, Shares				(2,920,000)			2,920,000
Issuance of common stock upon exercise of stock options, net of repurchases	3		0	$ 0	0	0	$ 0		3		0
Issuance of common stock upon exercise of stock options, net of repurchases, Shares							7,000
Vesting of early exercise options	16		0	0	0	0	$ 0		16		0
Stock-based compensation	16			0	0		0		16		0
Net loss	(5,116)		$ 0	$ 0	0	$ 0	0		0		(5,116)
Balance at Jun. 30, 2019	(48,698)				0		$ 0		(43,582)		(5,116)
Preferred Units, balance, Units at Jun. 30, 2019			0
Preferred Units, balance at Jun. 30, 2019			$ 0
Temporary equity, balance, Shares at Jun. 30, 2019						12,459,000
Temporary equity, balance at Jun. 30, 2019						$ 32,587
Members' equity, balance, Units at Jun. 30, 2019				0
Members' equity, balance at Jun. 30, 2019				$ 0
Balance, Shares at Jun. 30, 2019							2,927,000
Issuance of common stock upon exercise of stock options	16		0	0	0	0	$ 0		16		0
Issuance of common stock upon exercise of stock options, Shares							48,000
Vesting of early exercise options	2		0	0	0	0	$ 0		2		0
Stock-based compensation	22			0	0		0		22		0
Net loss	(6,668)		$ 0	$ 0	0	$ 0	0		0		(6,668)
Balance at Sep. 30, 2019	(55,326)				$ 0		$ 0		(43,542)		(11,784)
Preferred Units, balance, Units at Sep. 30, 2019			0
Preferred Units, balance at Sep. 30, 2019			$ 0
Temporary equity, balance, Shares at Sep. 30, 2019						12,459,000
Temporary equity, balance at Sep. 30, 2019						$ 32,587
Members' equity, balance, Units at Sep. 30, 2019				0
Members' equity, balance at Sep. 30, 2019				$ 0
Balance, Shares at Sep. 30, 2019							2,975,000
Balance at Dec. 31, 2019	$ (65,357)						$ 0		(43,172)		(22,185)
Temporary equity, balance, Shares at Dec. 31, 2019	37,267,000					37,267,000
Temporary equity, balance at Dec. 31, 2019	$ 134,720					$ 134,720
Balance, Shares at Dec. 31, 2019							2,989,000
Issuance of common stock upon exercise of stock options, net of repurchases	16					0	$ 0		16		0
Issuance of common stock upon exercise of stock options, net of repurchases, Shares							41,000
Vesting of early exercise options	14					0	$ 0		14		0
Issuance of convertible preferred stock, net of issuance costs						$ 2,200
Issuance of convertible preferred stock, net of issuance costs, Shares						538,000
Stock-based compensation	449						0		449		0
Net loss	(6,085)					$ 0	0		0		(6,085)
Balance at Mar. 31, 2020	(70,963)						$ 0		(42,693)		(28,270)
Temporary equity, balance, Shares at Mar. 31, 2020						37,805,000
Temporary equity, balance at Mar. 31, 2020						$ 136,920
Balance, Shares at Mar. 31, 2020							3,030,000
Balance at Dec. 31, 2019	$ (65,357)						$ 0		(43,172)		(22,185)
Temporary equity, balance, Shares at Dec. 31, 2019	37,267,000					37,267,000
Temporary equity, balance at Dec. 31, 2019	$ 134,720					$ 134,720
Balance, Shares at Dec. 31, 2019							2,989,000
Issuance of common stock upon exercise of stock options, Shares	106,000
Reclassification of warrant liability to equity due to adjustment from preferred stock warrant to common stock warrant upon completion of initial public offering	$ 120
Net loss	(28,080)
Balance at Sep. 30, 2020	$ 320,164						$ 4		370,425		(50,265)
Temporary equity, balance, Shares at Sep. 30, 2020	0					0
Temporary equity, balance at Sep. 30, 2020	$ 0					$ 0
Balance, Shares at Sep. 30, 2020							37,527,000
Balance at Mar. 31, 2020	(70,963)						$ 0		(42,693)		(28,270)
Temporary equity, balance, Shares at Mar. 31, 2020						37,805,000
Temporary equity, balance at Mar. 31, 2020						$ 136,920
Balance, Shares at Mar. 31, 2020							3,030,000
Vesting of early exercise options	34					0	$ 0		34		0
Issuance of stock, net of issuance costs, Value		$ 274,054						$ 2		$ 274,052		$ 0
Issuance of stock, net of issuance costs, Shares								16,560,000
Conversion of convertible preferred stock into common stock upon completion of initial public offering	136,920					$ (136,920)	$ 2		136,918		0
Conversion of convertible preferred stock into common stock upon completion of initial public offering, Shares						(37,805,000)	17,921,000
Reclassification of warrant liability to equity due to adjustment from preferred stock warrant to common stock warrant upon completion of initial public offering	120					$ 0	$ 0		120		0
Cashless exercise of common stock warrants	0						$ 0		0		0
Cashless exercise of common stock warrants, Shares							16,000
Stock-based compensation	687						$ 0		687		0
Net loss	(10,556)					$ 0	0		0		(10,556)
Balance at Jun. 30, 2020	330,296						$ 4		369,118		(38,826)
Temporary equity, balance, Shares at Jun. 30, 2020						0
Temporary equity, balance at Jun. 30, 2020						$ 0
Balance, Shares at Jun. 30, 2020							37,527,000
Vesting of early exercise options	11					0	$ 0		11		0
Stock-based compensation	1,296					0	0		1,296		0
Net loss	(11,439)					$ 0	0		0		(11,439)
Balance at Sep. 30, 2020	$ 320,164						$ 4		$ 370,425		$ (50,265)
Temporary equity, balance, Shares at Sep. 30, 2020	0					0
Temporary equity, balance at Sep. 30, 2020	$ 0					$ 0
Balance, Shares at Sep. 30, 2020							37,527,000

Condensed Statements of Conve_2

Condensed Statements of Convertible Preferred Stock/Units and Stockholders'/Members' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2020	Mar. 31, 2020
Convertible Preferred Stock
Stock issuance costs		$ 100
IPO | Common Stock
Stock issuance costs	$ 24,026

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net loss	$ (28,080)	$ (14,333)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation	258	265
Stock-based compensation expense	2,432	55
Amortization of discounts and loan issuance costs	29	57
Noncash interest expense	110	2,764
Change in fair value of preferred warrant liability	75	(1)
Changes in operating assets and liabilities:
Prepaid and other assets	(2,060)	(864)
Accounts payable and accrued liabilities	4,373	92
Accrued compensation	818	(67)
Operating lease right-of-use assets and liabilities, net	121	(59)
Deferred revenue	(2,120)	19,600
Net cash (used in) provided by operating activities	(24,044)	7,509
Cash flows from investing activities
Purchases of property and equipment	(855)	(144)
Net cash used in investing activities	(855)	(144)
Cash flows from financing activities
Proceeds from issuance of common stock in initial public offering, gross	298,080	0
Payment of issuance costs related to initial public offering	(24,026)	0
Proceeds from exercise of stock options/units, net of repurchases	16	58
Payments on long-term debt	(4,683)	(2,100)
Proceeds from issuance of Series C convertible preferred stock, net of issuance costs	2,200	0
Proceeds from issuance of convertible notes, net of issuance costs	0	19,451
Net cash provided by financing activities	271,587	17,409
Net increase in cash, cash equivalents and restricted cash	246,688	24,774
Cash, cash equivalents and restricted cash at beginning of period	94,578	3,090
Cash, cash equivalents and restricted cash at end of period	341,266	27,864
Supplemental disclosure of cash flow information:
Cash paid for interest	571	261
Supplemental schedule of noncash investing and financing activities:
Right-of-use assets obtained in exchange for operating lease liabilities	676	807
Costs incurred, but not paid, in connection with purchases of property and equipment included in accounts payable and accrued liabilities	67	21
Conversion of convertible preferred stock into common stock upon completion of initial public offering	136,920	0
Reclassification of warrant liability to equity due to adjustment from preferred stock warrant to common stock warrant upon completion of initial public offering	$ 120	$ 0

Description of Business and Bas

Description of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Description of Business and Basis of Presentation	1. Description of Basis of Description of Business Avidity Biosciences, Inc. (the Company or Avidity) is a biopharmaceutical company pioneering a new class of oligonucleotide-based therapies called Antibody Oligonucleotide Conjugates (AOCs) designed to overcome the current limitations of oligonucleotide-based therapies in order to treat a wide range of serious diseases. The Company utilizes its proprietary AOC platform to design, engineer and develop therapeutics that combine the tissue selectivity of monoclonal antibodies (mAbs) and the precision of oligonucleotide-based therapies. Initial Public Offering On June 16, 2020, the Company completed its initial public offering (IPO) in which it sold 16,560,000 shares of common stock at an offering price of $18.00 per share. Proceeds from the IPO, net of underwriting discounts, commissions and offering costs, were $274.1 million. In addition, each of the following occurred in connection with the completion of the IPO: • the conversion of all outstanding shares of convertible preferred stock into 17,921,069 shares of the Company’s common stock; • the adjustment of an outstanding warrant to purchase convertible preferred stock into a warrant to purchase 7,809 shares of the Company’s common stock; and • the amendment and restatement of the Company’s certificate of incorporation, authorizing 400,000,000 shares of common stock and 40,000,000 shares of undesignated preferred stock. Reverse Stock Split On June 4, 2020, the Company effected a one-for-2.1095 reverse stock split of its common stock (the Reverse Stock Split). The par value and the authorized shares of the common stock were not adjusted as a result of the Reverse Stock Split. All issued and outstanding common stock and the conversion ratio of the convertible preferred stock have been retroactively adjusted to reflect this Reverse Stock Split for all periods presented. Liquidity As of September 30, 2020, the Company has devoted substantially all of its resources to organizing and staffing the company, business planning, raising capital, developing its proprietary AOC platform, identifying potential product candidates, establishing its intellectual property portfolio and conducting research and preclinical studies, and providing other general and administrative support for these operations. In addition, the Company has a limited operating history, has incurred operating losses since inception and expects that it will continue to incur net losses into the foreseeable future as it continues the development of its product candidates and development programs. As of September 30, 2020, the Company had an accumulated deficit of $50.3 million and cash and cash equivalents of $341.1 million. The Company believes that existing cash and cash equivalents, including the net proceeds from the IPO, will be sufficient to fund the Company’s operations for at least 12 months from the date of the filing of this Form 10-Q. The Company plans to finance its future cash needs through equity offerings, debt financings or other capital sources, including potential collaborations, licenses and other similar arrangements. If the Company is not able to secure adequate additional funding, it may be forced to make reductions in spending, extend payment terms with suppliers, liquidate assets where possible, and/or delay or reduce the scope of its planned development programs. Any of these actions could materially harm the Company’s business, results of operations and future prospects. Basis of Presentation The accompanying unaudited interim condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and the rules and regulations of the Securities and Exchange Commission (SEC) related to a quarterly report on Form 10-Q. Certain information and note disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations. The unaudited interim condensed financial statements reflect all adjustments which, in the opinion of management, are necessary for a fair statement of the results for the periods presented. All such adjustments are of a normal and recurring nature. The operating results presented in these unaudited interim condensed financial statements are not necessarily indicative of the results that may be expected for any future periods. These unaudited interim condensed financial statements should be read in conjunction with the audited financial statements and the notes thereto for the year ended December 31, 2019 included in the Company’s Prospectus filed with the SEC on June 12, 2020 for its IPO.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Policies Use of Estimates The Company’s condensed financial statements accordance GAAP, which the Company and assumptions that impact the amounts of liabilities, revenues and expenses and the disclosure of contingent and liabilities in the financial statements and accompanying notes. The most significant estimates in the Company’s condensed financial statements to Although these on the Company’s knowledge of events and actions undertake the actual ultimately these and assumptions. 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 equivalents. Cash and cash equivalents include cash in readily available checking and money market accounts. Restricted cash represents cash held as collateral for the letter of credit required under the Company’s facility lease and is reported as a long-term asset in the accompanying condensed balance sheet. Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash deposits. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. Management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. Fair Value of Financial Instruments Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities • Level 2—Observable inputs, such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The asset’s or liability’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. None of the Company’s non-financial assets are recorded at fair value on a non-recurring basis. Prior to the completion of the IPO in June 2020, financial liabilities that were measured at fair value on a recurring basis included the preferred stock warrant liability. No transfers between levels have occurred during the periods presented. The carrying amounts reflected in the Company’s condensed balance sheets for prepaid and other assets and accounts payable and accrued liabilities approximate their fair values due to their short-term nature. As of December 31, 2019, the carrying value of the Company’s debt approximated fair value due to the interest being reflective of then-current market rates for debt with similar terms and conditions. The following table provides a reconciliation of the preferred stock warrant liability measured at fair value using Level 3 unobservable inputs (in thousands): Balance at December 31, 2019 $ 45 Change in fair value 75 Reclassification of preferred stock warrant liability to stockholders’ equity (120 ) Balance at September 30, 2020 $ — Property and Equipment Property and equipment, including leasehold improvements, are stated at cost less accumulated depreciation and amortization. Depreciation and amortization are recorded using the straight-line method over the estimated useful lives of the related assets, which ranges from three to five years. Leasehold improvements are amortized on a straight-line basis over the shorter of the estimated useful lives of the assets or the remaining lease term. Repairs and maintenance charges that do not increase the useful life of the assets are charged to operating expenses as incurred. Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. The Company has not recognized any impairment losses in any of the periods presented in these financial statements. Segment Information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by management in making decisions regarding resource allocation and assessing performance. The Company manages its operations as a single operating segment in the United States for the purposes of assessing performance and making operating decisions. Revenue Recognition To date, all the Company’s revenue has been derived from collaboration and research agreements. The terms of these arrangements include the following types of payments to the Company: non-refundable, upfront license fees; development, regulatory and commercial milestone payments; payments for research and development services provided by the Company or for manufacturing supply services the Company provides through its contract manufacturers; and royalties on net sales of licensed products. The Company performs the following steps in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of these agreements: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when, or as, the Company satisfies each performance obligation. The Company receives payments from its collaborators based on billing schedules established in each contract. Upfront and other payments may require deferral of revenue recognition to a future period until the Company performs its obligations under its research and collaboration arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. See Note 3 (Collaboration and License Agreement) for further information. Research and Development Costs Research and development costs are expensed as incurred and include salaries, benefits and stock-based compensation associated with research and development personnel, third-party research and development expenses, license fees, laboratory supplies, facilities, overhead costs, and consultants. Nonrefundable advance payments for goods and services that will be used in future research and development activities are capitalized and recorded as expense in the period that the Company receives the goods or when services are performed. Upfront and milestone payments to acquire contractual rights to licensed technology are recorded when incurred if there is uncertainty in the Company receiving future economic benefit from the acquired contractual rights. Income Taxes Deferred tax assets and liabilities are determined based on the differences between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company is subject to taxation in the United States and state jurisdictions. As of December 31, 2019, the Company’s tax years since inception are subject to examination by taxing authorities. Stock-Based Compensation Stock-based compensation expense for employee and non-employee stock option grants is recorded at the estimated fair value of the award as of the grant date and is recognized as expense on a straight-line basis over the requisite service period (usually the vesting period) of the stock-based award, net of actual forfeitures during the period. Stock-based compensation expense for employee stock purchases under the Company’s Employee Stock Purchase Plan (the ESPP) is recorded at the estimated fair value of the purchase as of the plan enrollment date and is recognized as expense on a straight-line basis over the applicable six-month ESPP offering period. The estimation of fair value for stock-based compensation requires management to make estimates and judgments about, among other things, the estimated life of options and volatility of the Company’s common stock. The judgments directly affect the amount of compensation expense that will be recognized. Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources. Net loss and comprehensive loss were the same for all periods presented. Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period, adjusted for the weighted-average number of common shares outstanding that are subject to repurchase or forfeiture. The Company has excluded 106,202 and 137,767 weighted-average shares subject to repurchase or forfeiture from the weighted-average number of common shares outstanding for the three and nine months ended September 30, 2020, respectively, and 195,378 and 221,266 weighted-average shares subject to repurchase or forfeiture from the weighted-average number of common shares outstanding for the three and nine months ended September 30, 2019, respectively. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as inclusion of the potentially dilutive securities would be antidilutive due to the Company’s net loss position. Potentially dilutive securities not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows (in common stock equivalent shares; in thousands): September 30, 2020 2019 Convertible preferred stock — 5,906 Warrant to purchase convertible preferred stock — 8 Warrant to purchase common stock — 9 Common stock options issued and outstanding 3,545 230 Common stock subject to repurchase or forfeiture 92 213 ESPP shares pending issuance 19 — Total 3,656 6,366 Recently Issued Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB) or other standard setting bodies that are adopted by the Company as of the specified effective date. The Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

Collaboration and License Agree

Collaboration and License Agreement	9 Months Ended
	Sep. 30, 2020
Collaboration And License Agreements [Abstract]
Collaboration and License Agreement	3. Collaboration and License Agreement Research Collaboration and License Agreement with Eli Lilly and Company In April 2019, the Company entered into a Research Collaboration and License Agreement (the Lilly Agreement) with Eli Lilly and Company (Lilly) for the discovery, development and commercialization of AOC products directed against certain targets in immunology and other select indications on a worldwide basis. Under the Lilly Agreement, the Company granted Lilly an exclusive, worldwide, royalty-bearing license, with the right to sublicense (subject to certain conditions), under the Company’s technology to research, develop, manufacture, and sell products containing AOCs that are directed to up to six mRNA targets. The Company retains the right to use its technology to perform its obligations under the Lilly Agreement and for all purposes not granted to Lilly. The Company agreed that it will not, itself or with a third party, research, develop, manufacture or commercialize or otherwise exploit any compound or product directed against targets subject to the Lilly Agreement. In consideration of the rights granted to Lilly under the Lilly Agreement, the Company received a one-time upfront fee of $20.0 million and is eligible to receive up to $60.0 million in development milestone payments, up to $140.0 million in regulatory milestone payments and up to $205.0 million in commercialization milestone payments per target. In addition, Lilly is obligated to reimburse the Company for research expenses, as defined in and, incurred under the Lilly Agreement. Lilly is obligated to pay the Company a tiered royalty ranging from the mid-single to low-double digits on worldwide annual net sales of licensed products, subject to specified and capped reductions for the market entry of biosimilar products, loss of patent coverage of licensed products and for payments owed to third parties for additional rights necessary to commercialize licensed products in the territory. Lilly’s royalty obligations and the Lilly Agreement will expire on a licensed product-by-licensed product and country-by-country basis on the later of ten years from the date of the first commercial sale or when there is no longer a valid patent claim covering such licensed product in such country. The Company has identified multiple promises to deliver goods and services, which include at inception of the agreement: (i) a license to technology and patents, information and know-how; and (ii) collaboration, including research services, technical and regulatory support provided by the Company. At inception and through September 30, 2020, the Company has identified one performance obligation for all the deliverables under the Lilly Agreement since the delivered elements are either not capable of being distinct or are not distinct within the context of the contract. Accordingly, the Company will recognize revenue for the fixed or determinable collaboration in an amount proportional to the collaboration expenses incurred and the total estimated collaboration expenses A reconciliation of the closing balance of deferred revenue related to the Lilly Agreement is as follows (in thousands): Balance at December 31, 2019 $ 18,940 Revenue recognized (2,120 ) Balance at September 30, 2020 $ 16,820 Concurrently with the execution of the Lilly Agreement, the Company issued a convertible promissory note to Lilly. In connection with the Series C financing in November 2019, all outstanding principal and interest accrued under the note converted into 4,576,342 shares of Series C convertible preferred stock. See Note 6 (Convertible Notes) for further discussion.

Property and Equipment

Property and Equipment	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Property and Equipment	4. Property and Equipment Property and equipment consist of the following (in thousands): September 30, 2020 December 31, 2019 Laboratory equipment $ 2,645 $ 1,755 Computers and software 91 65 Office furniture and equipment 43 37 Leasehold improvements 417 417 Property and equipment, gross 3,196 2,274 Less accumulated depreciation (1,901 ) (1,643 ) Total property and equipment, net $ 1,295 $ 631 Depreciation expense related to property and equipment was $0.1 million and $0.1 million for the three months ended September 30, 2020 and 2019, respectively, and $0.3 million and $0.3 million for the nine months ended September 30, 2020 and 2019, respectively.

Debt

Debt	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt	5. Debt The Company’s debt consisted of the following (in thousands): September 30, 2020 December 31, 2019 Current liabilities: Term loans $ — $ 2,800 Unamortized debt issuance costs — (25 ) Unamortized debt discount — (1 ) Loans payable, net of issuance costs and discount — 2,774 Non-current liabilities: Term loans — 1,400 Accrued end of term fees — 374 Unamortized debt issuance costs — (4 ) Loans payable, net of issuance costs and discount — 1,770 Total loans payable, net of issuance costs and discount $ — $ 4,544 Term Loan In June 2017, the Company entered into an amendment (the LSA Amendment) to the Amended and Restated Loan and Security Agreement (as amended, the LSA) with Silicon Valley Bank (SVB). Pursuant to the LSA Amendment, SVB agreed to make loans of up to $7.0 million, comprising (i) a $5.0 million term loan, funded at the closing date (the Term C Loan), and (ii) subject to the achievement of a specified milestone relating to the Company’s research, an additional term loan totaling up to $2.0 million (the Term D Loan), of which $4.1 million was used to repay the Company’s existing loan with SVB, in addition to the final payments totaling $0.4 million. The Term C Loan was scheduled to mature on June 1, 2021 and bore interest at an adjustable annual rate of the prime rate per the Wall Street Journal plus one-fifth of one percent (0.20%). The LSA Amendment provided an extension of the interest only period through June 1, 2019, upon the Term D Loan advance. Beginning July 1, 2019, the Company was required to repay the principal amount in 36 equal monthly installments, in addition to the monthly interest payment. In addition, a final payment of 6.5% of the funded amount, or $0.3 million, was due on the maturity date. The final payment fee was accrued as interest expense over the term of the loan and recorded in long-term debt, net of current portion. In August 2018, the Company entered into a second amendment to the LSA (the LSA Second Amendment). Pursuant to the LSA Second Amendment, SVB provided the Term D Loan of $2.0 million, upon the Company’s receipt of $3.0 million in convertible note financing. In addition, a final payment of 6.5% of the funded amount, or $0.1 million, was due on the maturity date. The Company accounted for the financing prospectively as a debt modification. On June 30, 2020, the Company voluntarily prepaid the aggregate outstanding principal balance of $2.8 million and final payments and accrued interest of $0.5 million related to the Term C and Term D Loans, and the LSA was terminated. In conjunction with the Term A and Term B Loans, the Company issued a warrant to SVB to purchase up to 16,474 shares of Series A convertible preferred stock at an exercise price of $2.2615 per share, exercisable at any time following the issuance, with a term of ten years. In connection with the completion of the IPO in June 2020, the preferred stock warrant was adjusted to become a warrant exercisable for 7,809 shares of common stock at an exercise price of $4.77 per share. In conjunction with the Term C Loan entered into in June 2017, the Company issued a warrant to SVB to purchase up to 9,442 shares of common stock at an exercise price of $0.53 per share, exercisable at any time following the issuance, with a term of seven years. The Company estimated the fair value of the warrants granted using the Black-Scholes option-pricing model and recorded the fair value as debt discounts, which were being amortized to interest expense using the effective interest method over the term of the loans. On June 17, 2020, the warrants were cashless exercised for an aggregate of 15,833 shares of common stock.

Convertible Notes

Convertible Notes	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Convertible Notes	6. Convertible Notes In 2018 and 2019, the Company issued convertible promissory notes in the aggregate principal amount of $3.0 million and $4.5 million, respectively (the 2018 Notes and 2019 Notes, respectively). The 2018 Notes and the 2019 Notes accrued interest at 8% and 10% per annum, respectively, and automatically converted into preferred equity in the next qualified financing of at least $10 million at 85% and 80%, respectively, of the per share price paid by the investors in such financing. Concurrently with the execution of the Lilly Agreement in April 2019, the Company issued a convertible promissory note to Lilly (the Lilly Note) and received cash proceeds of $15.0 million. The Lilly Note accrued simple interest of 8.0% per annum and, if not converted, would have matured in October 2020. All unpaid principal and interest were due at maturity. The 2018 Notes, 2019 Notes and the Lilly Note (collectively, the Notes) represented share settled debt that were accounted for at amortized cost by accreting the Notes to their redemption value over the life of the debt using the effective interest method. In connection with the Series C financing in November 2019, all outstanding principal and interest accrued under the Notes converted into 6,893,036 shares of Series C convertible preferred stock.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Lease Agreements The Company determines if an arrangement is a finance lease, operating lease or short-term lease at inception, or as applicable, and accounts for the arrangement under the relevant accounting literature. Currently, the Company is only party to non-cancellable office and laboratory space operating leases and a short-term office lease. Under the relevant guidance, the Company recognizes operating lease right-of-use (ROU) assets and liabilities based on the present value of the future minimum lease payments over the lease term at the commencement date, using the Company’s assumed incremental borrowing rate of 5.5%, and amortizes the ROU assets and liabilities over the lease term. Lease expense for operating leases is recognized on a straight-line basis over the lease term. The Company’s short-term lease is not subject to recognition of an ROU asset or liability or straight-line lease expense requirements. In March 2014, the Company entered into a non-cancellable operating lease for office and laboratory space with a lease term through November 2017. In July 2017, the Company entered into an amendment to this lease to extend the lease term through December 2021. On June 1, 2020, the Company entered into a second amendment to its existing operating lease (as amended, the 2014 Lease) and entered into a new non-cancellable temporary operating lease (the Temporary Lease) in connection with a newly executed non-cancellable operating lease for its headquarters location, commencing on July 1, 2021 (the New Lease). The lease term under both the 2014 Lease and the Temporary Lease ends 15 days after the commencement date of the New Lease in July 2021. The remaining monthly rental payments under the 2014 Lease and the rent under the Temporary Lease were abated beginning on June 1, 2020, given the execution of the New Lease. The total lease payments under the New Lease of $7.3 million were allocated amongst the 2014 Lease, Temporary Lease and New Lease based on the relative standalone price of the separate lease components. The New Lease will have a 5-year term upon commencement on July 1, 2021, with an initial monthly base rent of approximately $124,000, which will increase to approximately $139,000 during the last year of the New Lease's term. In addition, under the terms of the New Lease, the Company is required to maintain a letter of credit totaling $124,000 throughout the lease term. In June 2020, the Company adjusted the ROU asset and liability of the 2014 Lease to conform to the modification terms, and recorded an ROU asset and liability for the Temporary Lease upon occupancy. The Company will recognize an ROU asset and liability related to the New Lease upon occupancy, which is expected to occur in July 2021. As of September 30, 2020, the Company’s ROU assets and liabilities related to the 2014 Lease and the Temporary Lease are as follows (in thousands): ROU assets (included in other assets) $ 373 Lease liabilities, current portion (included in accounts payable and accrued liabilities) $ — Lease liabilities, net of current portion 689 Total lease liabilities $ 689 Maturities of the lease liabilities due under the 2014 Lease and the Temporary Lease are as follows (in thousands): Remaining in 2020 $ — 2021 12 2022 149 2023 154 2024 158 2025 163 2026 83 Total lease payments 719 Less imputed interest (30 ) Total operating lease liabilities 689 Less lease liabilities, current portion — Lease liabilities, net of current portion $ 689 Supplemental cash flow information related to operating leases was as follows (in thousands): Nine Months Ended September 30, 2020 2019 Cash paid included in operating cash flows $ 163 $ 286 Rent expense was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Operating leases $ 119 $ 75 $ 285 $ 226 Short-term lease 9 — 27 — Total rent expense $ 128 $ 75 $ 312 $ 226 Litigation Liabilities for loss contingencies arising from claims, assessments, litigation, fines, penalties, and other sources are recorded when it is probable that a liability has been incurred and the amount can be reasonably estimated. There are no matters currently outstanding for which any liabilities have been accrued.

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Stockholders’ Equity (Deficit)	8. Stockholders’ Equity (Deficit) Amended and Restated Certificate of Incorporation On June 16, 2020, the Company’s certificate of incorporation was amended and restated to authorize 400,000,000 shares of common stock and 40,000,000 shares of undesignated preferred stock, each with a par value of $0.0001 per share. Convertible Preferred Stock In connection with the completion of the IPO in June 2020, all of the outstanding shares of convertible preferred stock were converted into 17,921,069 shares of the Company’s common stock. As of December 31, 2019, the Company’s convertible preferred stock was classified as temporary equity on the accompanying balance sheet in accordance with authoritative guidance for the classification and measurement of potentially redeemable securities whose redemption is based upon certain change in control events outside of the Company’s control. Conversion On April 1, 2019, Avidity LLC, a Delaware limited liability company, was converted into Avidity Biosciences, Inc., a Delaware corporation. The entire membership interests of Avidity LLC were converted into securities of Avidity Biosciences, Inc. as follows: (i) each outstanding common unit of Avidity LLC was converted into one share of Avidity Biosciences, Inc.’s common stock; (ii) each outstanding Series A preferred unit of Avidity LLC converted into one share of Avidity Biosciences, Inc.’s Series A convertible preferred stock; and (iii) each outstanding Series B preferred unit of Avidity LLC converted into one share of Avidity Biosciences, Inc.’s Series B convertible preferred stock. All the property, rights, privileges, powers and franchises of Avidity LLC vested in Avidity Biosciences, Inc., and all debts, liabilities and duties of Avidity LLC became debts, liabilities and duties of Avidity Biosciences, Inc. All references to the former members’ equity accounts in Avidity LLC have been adjusted to reflect the equivalent number of Avidity Biosciences, Inc. shares of common stock. Upon completion of the conversion, the Company reclassified an accumulated deficit of $44.1 million from predecessor deficit to additional paid in capital. As of December 31, 2019, preferred stock consisted of the following (in thousands, except per share data): Series Shares Authorized Shares Issued and Outstanding Per Share Original Issue Price and Conversion Price Liquidation Preference Carrying Value Series A 4,367 4,350 $ 2.2615 $ 9,838 $ 9,773 Series B 8,108 8,108 2.8269 22,922 22,814 Series C 25,580 24,809 4.2812 106,210 102,133 Total 38,055 37,267 $ 138,970 $ 134,720 Equity Incentive Plan In January 2013, the Company adopted the 2013 Equity Incentive Plan (the 2013 Plan). The 2013 Plan provided for the issuance of incentive units to employees and nonemployees of the Company and non‑statutory unit options, restricted unit awards, unit appreciation rights, and unit bonuses to directors, employees and consultants of the Company. Under the 2013 Plan, 2,127,013 units were initially reserved for issuance. Upon the conversion of the Company to a C corporation, the 2013 Plan continued on the same terms and conditions. In 2019, the number of shares reserved under the 2013 Plan was increased to 4,771,615 shares. In June 2020, the Board of Directors adopted, and the Company’s stockholders approved, the 2020 Incentive Award Plan (the 2020 Plan), which became effective in connection with the IPO. Pursuant to the 2020 Plan, the Company ceased granting awards under the 2013 Plan. Under the 2020 Plan, the Company may grant stock options, restricted stock, dividend equivalents, restricted stock units, stock appreciation rights, and other stock or cash-based awards to individuals who are then employees, officers, non-employee directors or consultants of the Company. A total of 3,900,000 shares of common stock were initially reserved for issuance under the 2020 Plan. In addition, the number of shares of common stock available for issuance under the 2020 Plan will be increased annually on the first day of each fiscal year during the term of the 2020 Plan, beginning with the 2021 fiscal year, by an amount equal to the lesser of (a) 5% of the shares of common stock outstanding on the final day of the immediately preceding calendar year or (b) such smaller number of shares as determined by the Board of Directors. At September 30, 2020, 3,107,424 shares remain available for issuance under the 2020 Plan. Stock Options Options granted from the 2013 Plan and 2020 Plan are exercisable at various dates and will expire no more than ten years from their date of grant. Prior to the IPO, the exercise price of options was determined by the board of directors. Following the IPO, the Company grants options with an exercise price equal to the fair market value of the Company’s stock on the date of the option grant. Stock option activity for employee and nonemployee awards and related information is as follows (options in thousands): Number Weighted- Average Exercise Price Outstanding at December 31, 2019 1,667 $ 1.08 Granted 2,035 12.13 Exercised (106 ) 0.44 Forfeited (51 ) 1.24 Outstanding at September 30, 2020 3,545 $ 7.44 Employee Stock Purchase Plan In June 2020, the Company adopted the ESPP, which permits participants to contribute up to 15% of their eligible compensation during defined rolling six-month periods to purchase the Company’s common stock. The purchase price of the shares will be 85% of the lower of the fair market value of the Company’s common stock on the first day of trading of the offering period or on the applicable purchase date. A total of 325,000 shares of common stock was initially reserved for issuance under the ESPP. As of September 30, 2020, the Company has not issued any shares under the ESPP. The Company had an outstanding liability of $0.3 million at September 30, 2020, which is included in accounts payable and accrued liabilities on the balance sheet, for employee contributions to the ESPP for shares pending issuance at the end of the offering period. Stock-Based Compensation Expense The assumptions used in the Black-Scholes option pricing model to determine the fair value of the stock option/unit grants were as follows: Nine Months Ended September 30, 2020 2019 Risk-free interest rate 0.3% - 1.5% 1.4% - 2.7% Expected volatility 88% - 92% 84% - 88% Expected term (in years) 5.4 - 6.1 2.0 - 5.5 Expected dividend yield —% —% The allocation of stock-based compensation expense was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development expense $ 565 $ 6 $ 850 $ 22 General and administrative expense 731 16 1,582 33 Total stock-based compensation expense $ 1,296 $ 22 $ 2,432 $ 55 As of September 30, 2020, the unrecognized compensation cost related to outstanding time-based options was $23.1 million, which is expected to be recognized over a weighted-average period of 3.3 years.

COVID-19

COVID-19	9 Months Ended
	Sep. 30, 2020
Extraordinary And Unusual Items [Abstract]
COVID-19	9. COVID-19 The COVID-19 outbreak in the United States has caused significant business disruption. The extent of the impact of COVID-19 on the Company’s operational and financial performance will depend on certain developments, including the duration and spread of the outbreak, and its impact on the Company’s preclinical studies and clinical trials, employees and vendors, all of which are uncertain and cannot be predicted. In response to the COVID-19 outbreak, the Company has closed its executive offices with its administrative employees continuing their work remotely and limited the number of staff in its research and development laboratories. To date, the Company has not experienced material disruptions in its business operations. However, a prolonged outbreak could have a material adverse impact on the financial results and business operations of the Company, including the timing and ability of the Company to complete certain clinical trials and other efforts required to advance the development of its product candidates and raise additional capital. In response to the pandemic, the Coronavirus Aid, Relief and Economic Security Act (the CARES Act) was signed into law on March 27, 2020. The CARES Act, among other things, includes tax provisions relating to refundable payroll tax credits, deferment of employer’s social security payments, net operating loss utilization and carryback periods, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. The CARES Act had no impact on the Company’s income tax provision for the three and nine months ended September 30, 2020. The Company continues to evaluate the impact of the CARES Act on its financial position, results of operations and cash flows. The Company currently does not expect to apply for loans or grants under the CARES Act.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and the rules and regulations of the Securities and Exchange Commission (SEC) related to a quarterly report on Form 10-Q. Certain information and note disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations. The unaudited interim condensed financial statements reflect all adjustments which, in the opinion of management, are necessary for a fair statement of the results for the periods presented. All such adjustments are of a normal and recurring nature. The operating results presented in these unaudited interim condensed financial statements are not necessarily indicative of the results that may be expected for any future periods. These unaudited interim condensed financial statements should be read in conjunction with the audited financial statements and the notes thereto for the year ended December 31, 2019 included in the Company’s Prospectus filed with the SEC on June 12, 2020 for its IPO.
Use of Estimates	Use of Estimates The Company’s condensed financial statements accordance GAAP, which the Company and assumptions that impact the amounts of liabilities, revenues and expenses and the disclosure of contingent and liabilities in the financial statements and accompanying notes. The most significant estimates in the Company’s condensed financial statements to Although these on the Company’s knowledge of events and actions undertake the actual ultimately these and assumptions.
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 equivalents. Cash and cash equivalents include cash in readily available checking and money market accounts. Restricted cash represents cash held as collateral for the letter of credit required under the Company’s facility lease and is reported as a long-term asset in the accompanying condensed balance sheet.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash deposits. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. Management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1—Quoted prices in active markets for identical assets or liabilities • Level 2—Observable inputs, such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The asset’s or liability’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. None of the Company’s non-financial assets are recorded at fair value on a non-recurring basis. Prior to the completion of the IPO in June 2020, financial liabilities that were measured at fair value on a recurring basis included the preferred stock warrant liability. No transfers between levels have occurred during the periods presented. The carrying amounts reflected in the Company’s condensed balance sheets for prepaid and other assets and accounts payable and accrued liabilities approximate their fair values due to their short-term nature. As of December 31, 2019, the carrying value of the Company’s debt approximated fair value due to the interest being reflective of then-current market rates for debt with similar terms and conditions. The following table provides a reconciliation of the preferred stock warrant liability measured at fair value using Level 3 unobservable inputs (in thousands): Balance at December 31, 2019 $ 45 Change in fair value 75 Reclassification of preferred stock warrant liability to stockholders’ equity (120 ) Balance at September 30, 2020 $ —
Property and Equipment	Property and Equipment Property and equipment, including leasehold improvements, are stated at cost less accumulated depreciation and amortization. Depreciation and amortization are recorded using the straight-line method over the estimated useful lives of the related assets, which ranges from three to five years. Leasehold improvements are amortized on a straight-line basis over the shorter of the estimated useful lives of the assets or the remaining lease term. Repairs and maintenance charges that do not increase the useful life of the assets are charged to operating expenses as incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. The Company has not recognized any impairment losses in any of the periods presented in these financial statements.
Segment Information	Segment Information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by management in making decisions regarding resource allocation and assessing performance. The Company manages its operations as a single operating segment in the United States for the purposes of assessing performance and making operating decisions.
Revenue Recognition	Revenue Recognition To date, all the Company’s revenue has been derived from collaboration and research agreements. The terms of these arrangements include the following types of payments to the Company: non-refundable, upfront license fees; development, regulatory and commercial milestone payments; payments for research and development services provided by the Company or for manufacturing supply services the Company provides through its contract manufacturers; and royalties on net sales of licensed products. The Company performs the following steps in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of these agreements: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when, or as, the Company satisfies each performance obligation. The Company receives payments from its collaborators based on billing schedules established in each contract. Upfront and other payments may require deferral of revenue recognition to a future period until the Company performs its obligations under its research and collaboration arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. See Note 3 (Collaboration and License Agreement) for further information.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred and include salaries, benefits and stock-based compensation associated with research and development personnel, third-party research and development expenses, license fees, laboratory supplies, facilities, overhead costs, and consultants. Nonrefundable advance payments for goods and services that will be used in future research and development activities are capitalized and recorded as expense in the period that the Company receives the goods or when services are performed. Upfront and milestone payments to acquire contractual rights to licensed technology are recorded when incurred if there is uncertainty in the Company receiving future economic benefit from the acquired contractual rights.
Income Taxes	Income Taxes Deferred tax assets and liabilities are determined based on the differences between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company is subject to taxation in the United States and state jurisdictions. As of December 31, 2019, the Company’s tax years since inception are subject to examination by taxing authorities.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense for employee and non-employee stock option grants is recorded at the estimated fair value of the award as of the grant date and is recognized as expense on a straight-line basis over the requisite service period (usually the vesting period) of the stock-based award, net of actual forfeitures during the period. Stock-based compensation expense for employee stock purchases under the Company’s Employee Stock Purchase Plan (the ESPP) is recorded at the estimated fair value of the purchase as of the plan enrollment date and is recognized as expense on a straight-line basis over the applicable six-month ESPP offering period. The estimation of fair value for stock-based compensation requires management to make estimates and judgments about, among other things, the estimated life of options and volatility of the Company’s common stock. The judgments directly affect the amount of compensation expense that will be recognized.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources. Net loss and comprehensive loss were the same for all periods presented.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period, adjusted for the weighted-average number of common shares outstanding that are subject to repurchase or forfeiture. The Company has excluded 106,202 and 137,767 weighted-average shares subject to repurchase or forfeiture from the weighted-average number of common shares outstanding for the three and nine months ended September 30, 2020, respectively, and 195,378 and 221,266 weighted-average shares subject to repurchase or forfeiture from the weighted-average number of common shares outstanding for the three and nine months ended September 30, 2019, respectively. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as inclusion of the potentially dilutive securities would be antidilutive due to the Company’s net loss position. Potentially dilutive securities not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows (in common stock equivalent shares; in thousands): September 30, 2020 2019 Convertible preferred stock — 5,906 Warrant to purchase convertible preferred stock — 8 Warrant to purchase common stock — 9 Common stock options issued and outstanding 3,545 230 Common stock subject to repurchase or forfeiture 92 213 ESPP shares pending issuance 19 — Total 3,656 6,366
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB) or other standard setting bodies that are adopted by the Company as of the specified effective date. The Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Schedule of Reconciliation of Preferred Stock Warrant Liability Measured at Fair Value Using Level 3 Unobservable Inputs	The following table provides a reconciliation of the preferred stock warrant liability measured at fair value using Level 3 unobservable inputs (in thousands): Balance at December 31, 2019 $ 45 Change in fair value 75 Reclassification of preferred stock warrant liability to stockholders’ equity (120 ) Balance at September 30, 2020 $ —
Schedule of Potentially Dilutive Securities not Included in Calculation of Diluted Net Loss Per Share	Potentially dilutive securities not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows (in common stock equivalent shares; in thousands): September 30, 2020 2019 Convertible preferred stock — 5,906 Warrant to purchase convertible preferred stock — 8 Warrant to purchase common stock — 9 Common stock options issued and outstanding 3,545 230 Common stock subject to repurchase or forfeiture 92 213 ESPP shares pending issuance 19 — Total 3,656 6,366

Collaboration and License Agr_2

Collaboration and License Agreement (Tables)	9 Months Ended
	Sep. 30, 2020
Collaboration And License Agreements [Abstract]
Summary of Reconciliation of Deferred Revenue Related to Lilly Agreement	A reconciliation of the closing balance of deferred revenue related to the Lilly Agreement is as follows (in thousands): Balance at December 31, 2019 $ 18,940 Revenue recognized (2,120 ) Balance at September 30, 2020 $ 16,820

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consist of the following (in thousands): September 30, 2020 December 31, 2019 Laboratory equipment $ 2,645 $ 1,755 Computers and software 91 65 Office furniture and equipment 43 37 Leasehold improvements 417 417 Property and equipment, gross 3,196 2,274 Less accumulated depreciation (1,901 ) (1,643 ) Total property and equipment, net $ 1,295 $ 631

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule of Debt	The Company’s debt consisted of the following (in thousands): September 30, 2020 December 31, 2019 Current liabilities: Term loans $ — $ 2,800 Unamortized debt issuance costs — (25 ) Unamortized debt discount — (1 ) Loans payable, net of issuance costs and discount — 2,774 Non-current liabilities: Term loans — 1,400 Accrued end of term fees — 374 Unamortized debt issuance costs — (4 ) Loans payable, net of issuance costs and discount — 1,770 Total loans payable, net of issuance costs and discount $ — $ 4,544

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Schedule of ROU Assets and Liabilities Related to 2014 Lease and Temporary Lease	As of September 30, 2020, the Company’s ROU assets and liabilities related to the 2014 Lease and the Temporary Lease are as follows (in thousands): ROU assets (included in other assets) $ 373 Lease liabilities, current portion (included in accounts payable and accrued liabilities) $ — Lease liabilities, net of current portion 689 Total lease liabilities $ 689
Schedule of Maturities of Lease Liabilities due under 2014 Lease and Temporary Lease	Maturities of the lease liabilities due under the 2014 Lease and the Temporary Lease are as follows (in thousands): Remaining in 2020 $ — 2021 12 2022 149 2023 154 2024 158 2025 163 2026 83 Total lease payments 719 Less imputed interest (30 ) Total operating lease liabilities 689 Less lease liabilities, current portion — Lease liabilities, net of current portion $ 689
Supplemental Cash Flow Information Related to Operating Leases	Supplemental cash flow information related to operating leases was as follows (in thousands): Nine Months Ended September 30, 2020 2019 Cash paid included in operating cash flows $ 163 $ 286
Schedule of Rent Expense	Rent expense was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Operating leases $ 119 $ 75 $ 285 $ 226 Short-term lease 9 — 27 — Total rent expense $ 128 $ 75 $ 312 $ 226

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) (Tables)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Summary of Preferred Stock	As of December 31, 2019, preferred stock consisted of the following (in thousands, except per share data): Series Shares Authorized Shares Issued and Outstanding Per Share Original Issue Price and Conversion Price Liquidation Preference Carrying Value Series A 4,367 4,350 $ 2.2615 $ 9,838 $ 9,773 Series B 8,108 8,108 2.8269 22,922 22,814 Series C 25,580 24,809 4.2812 106,210 102,133 Total 38,055 37,267 $ 138,970 $ 134,720
Summary of Stock Option Activity	Stock option activity for employee and nonemployee awards and related information is as follows (options in thousands): Number Weighted- Average Exercise Price Outstanding at December 31, 2019 1,667 $ 1.08 Granted 2,035 12.13 Exercised (106 ) 0.44 Forfeited (51 ) 1.24 Outstanding at September 30, 2020 3,545 $ 7.44
Schedule of Assumptions Used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option/Unit Grants	The assumptions used in the Black-Scholes option pricing model to determine the fair value of the stock option/unit grants were as follows: Nine Months Ended September 30, 2020 2019 Risk-free interest rate 0.3% - 1.5% 1.4% - 2.7% Expected volatility 88% - 92% 84% - 88% Expected term (in years) 5.4 - 6.1 2.0 - 5.5 Expected dividend yield —% —%
Schedule of Allocated Stock-based Compensation Expense	The allocation of stock-based compensation expense was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development expense $ 565 $ 6 $ 850 $ 22 General and administrative expense 731 16 1,582 33 Total stock-based compensation expense $ 1,296 $ 22 $ 2,432 $ 55

Description of Business and B_2

Description of Business and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands	Jun. 16, 2020USD ($)$ / sharesshares	Jun. 04, 2020	Jun. 30, 2020shares	Jun. 30, 2020shares	Sep. 30, 2020USD ($)shares	Dec. 31, 2019USD ($)shares
Description Of Business And Basis Of Presentation [Line Items]
Common stock, shares authorized	400,000,000				400,000,000	52,042,000
Preferred stock, shares authorized	40,000,000				40,000,000	0
Reverse stock split, description					On June 4, 2020, the Company effected a one-for-2.1095 reverse stock split of its common stock (the Reverse Stock Split).
Stockholders' equity note, stock split, conversion ratio		2.1095
Accumulated deficit | $					$ 50,265	$ 22,185
Cash and cash equivalents | $					$ 341,142	$ 94,578
Common Stock
Description Of Business And Basis Of Presentation [Line Items]
Outstanding shares of convertible preferred stock converted into common stock				17,921,000
Initial Public Offering
Description Of Business And Basis Of Presentation [Line Items]
Sale of stock number of shares issued in transaction	16,560,000
Sale of stock, price per share | $ / shares	$ 18
Proceeds from the IPO, net of underwriting discounts, commissions and offering costs | $	$ 274,100
Outstanding shares of convertible preferred stock converted into common stock	17,921,069
Initial Public Offering | Undesignated Preferred Stock
Description Of Business And Basis Of Presentation [Line Items]
Preferred stock, shares authorized	40,000,000
Initial Public Offering | Common Stock
Description Of Business And Basis Of Presentation [Line Items]
Outstanding shares of convertible preferred stock converted into common stock			17,921,069
Warrant to purchase of common stock	7,809
Common stock, shares authorized	400,000,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)shares	Sep. 30, 2019shares	Sep. 30, 2020USD ($)Segmentshares	Sep. 30, 2019shares
Summary Of Significant Accounting Policies [Line Items]
Transfers of assets measured on recurring basis out of Level 1 into Level 2	$ 0		$ 0
Transfers of assets measured on recurring basis out of Level 2 into Level 1	0		0
Transfers of liabilities measured on recurring basis out of Level 1 into Level 2	0		0
Transfers of liabilities measured on recurring basis out of Level 2 into Level 1	$ 0		0
Transfers of financial instrument classified as liability into level 3			0
Transfers of financial instrument classified as liability out of level 3			0
Transfers of financial instrument classified as asset into level 3			0
Transfers of financial instrument classified as asset out of level 3			$ 0
Number of operating segment | Segment			1
Weighted-average shares subject to repurchase or forfeiture | shares	106,202	195,378	137,767	221,266
Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets			3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of assets			5 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Reconciliation of Preferred Stock Warrant Liability Measured at Fair Value Using Level 3 Unobservable Inputs (Details) - Level 3 - Recurring $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at December 31, 2019	$ 45
Change in fair value	75
Reclassification of preferred stock warrant liability to stockholders’ equity	(120)
Balance at September 30, 2020	$ 0

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities not Included in Calculation of Diluted Net Loss Per Share (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	3,656	6,366
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	0	5,906
Warrant | Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	0	9
Warrant | Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	0	8
Common Stock Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	3,545	230
Common Stock Subject to Repurchase or Forfeiture
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	92	213
ESPP Shares Pending Issuance
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	19	0

Collaboration and License Agr_3

Collaboration and License Agreements - Additional Information (Details)	Nov. 30, 2019shares	Apr. 30, 2019USD ($)Product	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)Obligation	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized			$ 1,746,000	$ 650,000	$ 4,645,000	$ 874,000
Lilly Note | Series C Convertible Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Conversion of convertible note payable to preferred stock | shares	4,576,342
Research Collaboration and License Agreement with Eli Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fees received		$ 20,000,000
License agreement expiry period		10 years
Number of performance obligation | Obligation					1
Period for expects performance obligation					5 years
Revenue recognized			1,700,000	$ 700,000	$ 4,600,000	$ 900,000
Deferred revenue			$ 16,820,000		$ 16,820,000		$ 18,940,000
Research Collaboration and License Agreement with Eli Lilly | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Rights to antibody oligonucleotide conjugates for messengers RNA targets. | Product		6
Development milestone payment eligible to receive per target		$ 60,000,000
Regulatory milestone payment eligible to receive per target		140,000,000
Commercialization milestone payment eligible to receive		$ 205,000,000

Collaboration and License Agr_4

Collaboration and License Agreements - Reconciliation of Deferred Revenue Related to Lilly Agreement (Details) - Research Collaboration and License Agreement with Eli Lilly $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance	$ 18,940
Revenue recognized	(2,120)
Balance	$ 16,820

Property,and Equipment - Schedu

Property,and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,196	$ 2,274
Less accumulated depreciation	(1,901)	(1,643)
Total property and equipment, net	1,295	631
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,645	1,755
Computers and Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	91	65
Office Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	43	37
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 417	$ 417

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Property Plant And Equipment [Line Items]
Depreciation expenses related to property and equipment			$ 258	$ 265
Property and Equipment
Property Plant And Equipment [Line Items]
Depreciation expenses related to property and equipment	$ 100	$ 100	$ 300	$ 300

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current liabilities:
Term loans	$ 0	$ 2,800
Unamortized debt issuance costs	0	(25)
Unamortized debt discount	0	(1)
Loans payable, net of issuance costs and discount	0	2,774
Non-current liabilities:
Term loans	0	1,400
Accrued end of term fees	0	374
Unamortized debt issuance costs	0	(4)
Loans payable, net of issuance costs and discount	0	1,770
Total loans payable, net of issuance costs and discount	$ 0	$ 4,544

Debt - Additional Information (

Debt - Additional Information (Details)	Jun. 17, 2020shares	Jun. 30, 2020USD ($)$ / sharesshares	Aug. 31, 2018USD ($)	Jun. 30, 2017USD ($)Installment$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares	Sep. 30, 2019USD ($)
Debt Instrument [Line Items]
Repayment of existing loan					$ 4,683,000	$ 2,100,000
Proceeds from notes					$ 0	$ 19,451,000
Common Stock
Debt Instrument [Line Items]
Warrant exercisable | shares		7,809
Exercise price of warrant | $ / shares		$ 4.77
Cashless exercise of warrants | shares	15,833
SVB
Debt Instrument [Line Items]
Repayment of existing loan				$ 4,100,000
Debt instrument final payments				$ 400,000
SVB | Convertible Notes
Debt Instrument [Line Items]
Proceeds from notes			$ 3,000,000
SVB | Term C Loan | Common Stock
Debt Instrument [Line Items]
Warrant term					7 years
Exercise price of warrant | $ / shares				$ 0.53
SVB | Term C Loan | Common Stock | Maximum
Debt Instrument [Line Items]
Warrant to purchase common stock | shares				9,442
SVB | Term A And Term B Loans | Series A Convertible Preferred Stock
Debt Instrument [Line Items]
Exercise price of warrant | $ / shares					$ 2.2615
Warrant term					10 years
SVB | Term A And Term B Loans | Series A Convertible Preferred Stock | Maximum
Debt Instrument [Line Items]
Warrant to purchase convertible preferred stock | shares					16,474
SVB | LSA Amendment
Debt Instrument [Line Items]
Loan facility maximum borrowing capacity				$ 7,000,000
SVB | LSA Amendment | Term C Loan
Debt Instrument [Line Items]
Face amount of loans				5,000,000
Debt instrument final payments				$ 300,000
Maturity date				Jun. 1, 2021
Basis spread on variable rate				0.20%
Frequency of periodic payment principal					36 equal monthly
Number of equal monthly installments of principal | Installment				36
Frequency of periodic payment interest					monthly
Debt instrument final payment percentage				6.50%
SVB | LSA Amendment | Term D Loan
Debt Instrument [Line Items]
Face amount of loans			2,000,000
SVB | LSA Second Amendment | Term D Loan
Debt Instrument [Line Items]
Debt instrument final payments			$ 100,000
Debt instrument final payment percentage			6.50%
Proceeds from issuance of long-term debt			$ 2,000,000
SVB | LSA | Term C And D Loans
Debt Instrument [Line Items]
Loans prepaid amount		$ 2,800,000
Payment of final payment and accrued interest		$ 500,000

Convertible Notes - Additional

Convertible Notes - Additional Information (Details) - USD ($)	Nov. 30, 2019	Apr. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Proceeds from issuance of convertible notes			$ 0	$ 19,451,000
Convertible Notes | Series C Convertible Preferred Stock
Debt Instrument [Line Items]
Conversion of convertible notes payable to preferred stock	6,893,036
2018 Notes
Debt Instrument [Line Items]
Face amount of loans						$ 3,000,000
Convertible promissory notes accrued interest rate						8.00%
Convertible promissory notes conversion percentage on per share price paid by investors						85.00%
Qualified financing of convertible promissory notes converted into preferred equity						$ 10,000,000
2019 Notes
Debt Instrument [Line Items]
Face amount of loans					$ 4,500,000
Convertible promissory notes accrued interest rate					10.00%
Convertible promissory notes conversion percentage on per share price paid by investors					80.00%
Qualified financing of convertible promissory notes converted into preferred equity					$ 10,000,000
Lilly Note
Debt Instrument [Line Items]
Convertible promissory notes accrued interest rate		8.00%
Proceeds from issuance of convertible notes		$ 15,000,000
Maturity date		2020-10
Lilly Note | Series C Convertible Preferred Stock
Debt Instrument [Line Items]
Conversion of convertible notes payable to preferred stock	4,576,342

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2020
Commitments and Contingencies [Line Items]
Operating lease, description		Currently, the Company is only party to non-cancellable office and laboratory space operating leases and a short-term office lease. Under the relevant guidance, the Company recognizes operating lease right-of-use (ROU) assets and liabilities based on the present value of the future minimum lease payments over the lease term at the commencement date, using the Company’s assumed incremental borrowing rate of 5.5%, and amortizes the ROU assets and liabilities over the lease term. Lease expense for operating leases is recognized on a straight-line basis over the lease term. The Company’s short-term lease is not subject to recognition of an ROU asset or liability or straight-line lease expense requirements.
Incremental borrowing rate		5.50%
Loss contingencies accrued		$ 0
Lease Term through November 2017 | Office and Laboratory Space
Commitments and Contingencies [Line Items]
Operating lease, term of contract, description		In March 2014, the Company entered into a non-cancellable operating lease for office and laboratory space with a lease term through November 2017
Lease Term through December 2021 | Office and Laboratory Space
Commitments and Contingencies [Line Items]
Operating lease, term of contract, description		In July 2017, the Company entered into an amendment to this lease to extend the lease term through December 2021.
New Lease | Office and Laboratory Space
Commitments and Contingencies [Line Items]
Operating lease, lease not yet commenced, description		On June 1, 2020, the Company entered into a second amendment to its existing operating lease (as amended, the 2014 Lease) and entered into a new non-cancellable temporary operating lease (the Temporary Lease) in connection with a newly executed non-cancellable operating lease for its headquarters location, commencing on July 1, 2021 (the New Lease).
Operating lease, lease not yet commenced, lease payment under new lease		$ 7,300,000
Operating lease, lease not yet commenced, term of contract	5 years
Operating lease, lease not yet commenced, initial monthly base rent	$ 124,000
Operating lease, lease not yet commenced, monthly base rent for last year lease	139,000
Letter of credit	$ 124,000
Temporary Lease | Office and Laboratory Space
Commitments and Contingencies [Line Items]
Operating lease expiration period, description		The lease term under both the 2014 Lease and the Temporary Lease ends 15 days after the commencement date of the New Lease in July 2021.
Operating lease lease expiration period	15 days

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of ROU Assets and Liabilities Related to 2014 Lease and Temporary Lease (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
ROU assets (included in other assets)	$ 373
Operating lease, right-of-use asset, statement of financial position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Lease liabilities, current portion (included in accounts payable and accrued liabilities)	$ 0
Operating lease, liability, current, statement of financial position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrent
Lease liabilities, net of current portion	$ 689	$ 393
Total lease liabilities	$ 689

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Maturities of Lease Liabilities due under 2014 Lease and Temporary Lease (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Remaining in 2020	$ 0
2021	12
2022	149
2023	154
2024	158
2025	163
2026	83
Total lease payments	719
Less imputed interest	(30)
Total lease liabilities	689
Less lease liabilities, current portion	0
Lease liabilities, net of current portion	$ 689	$ 393

Commitments and Contingencies_4

Commitments and Contingencies - Supplemental Cash Flow Information Related to Operating Leases (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Cash paid included in operating cash flows	$ 163	$ 286

Commitments and Contingencies_5

Commitments and Contingencies - Schedule of Rent Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Operating leases	$ 119	$ 75	$ 285	$ 226
Short-term lease	9	0	27	0
Total rent expense	$ 128	$ 75	$ 312	$ 226

Stockholders' Equity (Deficit_2

Stockholders' Equity (Deficit) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 16, 2020	Apr. 01, 2019	Jun. 30, 2020	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019	Jan. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares authorized	400,000,000				400,000,000	52,042,000
Preferred stock undesignated shares authorized	40,000,000				40,000,000	0
Common stock par value per share	$ 0.0001				$ 0.0001	$ 0.0001
Preferred stock par value per share	$ 0.0001				$ 0.0001	$ 0.0001
Reclassified accumulated deficit from predecessor deficit to additional paid in capital		$ 44.1
Time-based Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost					$ 23.1
Weighted-average period of unrecognized compensation cost					3 years 3 months 18 days
2013 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Units initially reserved for issuance							2,127,013
Increased to number of shares reserved under plan						4,771,615
2013 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration period					10 years
2020 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock initially reserved for issuance			3,900,000	3,900,000
Percentage of shares of common stock outstanding on final day of immediately preceding calendar year			5.00%	5.00%
Number of remaining shares available for issuance					3,107,424
2020 Incentive Award Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration period					10 years
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock initially reserved for issuance			325,000	325,000
Participant maximum contribution as percentage of eligible compensation			15.00%	15.00%
Percentage of purchase price of shares of lower of fair market value			85.00%
Shares issued under ESPP					0
Employee Stock Purchase Plan | Accounts Payable and Accrued Liabilities
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding liability					$ 0.3
Series A Convertible Preferred Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Preferred unit converted into convertible preferred stock		1
Series B Convertible Preferred Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Preferred unit converted into convertible preferred stock		1
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Convertible preferred stock converted into shares of common stock				17,921,000
Common unit converted into common stock		1
IPO
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Convertible preferred stock converted into shares of common stock	17,921,069
IPO | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares authorized	400,000,000
Convertible preferred stock converted into shares of common stock			17,921,069

Stockholders' Equity (Deficit_3

Stockholders' Equity (Deficit) - Summary of Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Shares Authorized	0	38,055,000
Shares Issued and Outstanding		37,267,000
Liquidation Preference		$ 138,970
Carrying Value	$ 0	$ 134,720
Series A
Temporary Equity [Line Items]
Shares Authorized		4,367,000
Shares Issued and Outstanding		4,350,000
Per Share Original Issue Price and Conversion Price		$ 2.2615
Liquidation Preference		$ 9,838
Carrying Value		$ 9,773
Series B
Temporary Equity [Line Items]
Shares Authorized		8,108,000
Shares Issued and Outstanding		8,108,000
Per Share Original Issue Price and Conversion Price		$ 2.8269
Liquidation Preference		$ 22,922
Carrying Value		$ 22,814
Series C
Temporary Equity [Line Items]
Shares Authorized		25,580,000
Shares Issued and Outstanding		24,809,000
Per Share Original Issue Price and Conversion Price		$ 4.2812
Liquidation Preference		$ 106,210
Carrying Value		$ 102,133

Stockholders' Equity (Deficit_4

Stockholders' Equity (Deficit) - Summary of Stock Option Activity (Details) shares in Thousands	9 Months Ended
	Sep. 30, 2020$ / sharesshares
Number
Outstanding at December 31, 2019 | shares	1,667
Granted | shares	2,035
Exercised | shares	(106)
Forfeited | shares	(51)
Outstanding at September 30, 2020 | shares	3,545
Weighted-Average Exercise Price
Outstanding at December 31, 2019 | $ / shares	$ 1.08
Granted | $ / shares	12.13
Exercised | $ / shares	0.44
Forfeited | $ / shares	1.24
Outstanding at September 30, 2020 | $ / shares	$ 7.44

Stockholders' Equity (Deficit_5

Stockholders' Equity (Deficit) - Schedule of Assumptions Used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option/Unit Grants (Details)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	0.30%	1.40%
Expected volatility	88.00%	84.00%
Expected term (in years)	5 years 4 months 24 days	2 years
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	1.50%	2.70%
Expected volatility	92.00%	88.00%
Expected term (in years)	6 years 1 month 6 days	5 years 6 months

Stockholders' Equity (Deficit_6

Stockholders' Equity (Deficit) - Schedule of Allocated Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,296	$ 22	$ 2,432	$ 55
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	565	6	850	22
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 731	$ 16	$ 1,582	$ 33