Condensed Consolidated Statements of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Series B preferred stock	Common stock	Additional paid-in capital	Accumulated other comprehensive income	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2018	33,668,075
Beginning balance at Dec. 31, 2018	$ 60,770
Ending balance (in shares) at Mar. 31, 2019	33,668,075
Ending balance at Mar. 31, 2019	$ 60,770
Beginning balance (in shares) at Dec. 31, 2018			2,173,684
Beginning balance at Dec. 31, 2018	(15,542)		$ 1	$ 169	$ 0	$ (15,712)
Common stock
Grant of restricted common stock awards (in shares)			46,416
Grant of restricted common stock awards	0
Stock-based compensation	91			91
Net loss	(3,828)					(3,828)
Ending balance (in shares) at Mar. 31, 2019			2,220,100
Ending balance at Mar. 31, 2019	$ (19,279)		$ 1	260	0	(19,540)
Beginning balance (in shares) at Dec. 31, 2018	33,668,075
Beginning balance at Dec. 31, 2018	$ 60,770
Ending balance (in shares) at Sep. 30, 2019	45,419,229
Ending balance at Sep. 30, 2019	$ 115,840
Beginning balance (in shares) at Dec. 31, 2018			2,173,684
Beginning balance at Dec. 31, 2018	(15,542)		$ 1	169	0	(15,712)
Common stock
Change in unrealized (loss) gain on investments	0
Net loss	(25,383)
Ending balance (in shares) at Sep. 30, 2019			2,220,100
Ending balance at Sep. 30, 2019	$ (39,792)		$ 1	1,302	0	(41,095)
Beginning balance (in shares) at Mar. 31, 2019	33,668,075
Beginning balance at Mar. 31, 2019	$ 60,770
Ending balance (in shares) at Jun. 30, 2019	33,668,075
Ending balance at Jun. 30, 2019	$ 60,770
Beginning balance (in shares) at Mar. 31, 2019			2,220,100
Beginning balance at Mar. 31, 2019	(19,279)		$ 1	260	0	(19,540)
Common stock
Stock-based compensation	192			192
Net loss	(12,287)					(12,287)
Ending balance (in shares) at Jun. 30, 2019			2,220,100
Ending balance at Jun. 30, 2019	$ (31,374)		$ 1	452	0	(31,827)
Convertible preferred stock
Issuance of series B convertible preferred stock, net (in shares)		11,751,154
Issuance of series B convertible preferred stock, net		$ 55,070
Ending balance (in shares) at Sep. 30, 2019	45,419,229
Ending balance at Sep. 30, 2019	$ 115,840
Common stock
Stock-based compensation	850			850
Change in unrealized (loss) gain on investments	0
Net loss	(9,268)					(9,268)
Ending balance (in shares) at Sep. 30, 2019			2,220,100
Ending balance at Sep. 30, 2019	$ (39,792)		$ 1	1,302	0	(41,095)
Beginning balance (in shares) at Dec. 31, 2019	64,839,353
Beginning balance at Dec. 31, 2019	$ 200,573
Convertible preferred stock
Conversion of preferred stock to common stock upon closing of the initial public offering (in shares)	(64,839,353)
Conversion of preferred stock to common stock upon closing of the initial public offering	$ (200,573)
Ending balance (in shares) at Mar. 31, 2020	0
Ending balance at Mar. 31, 2020	$ 0
Beginning balance (in shares) at Dec. 31, 2019	2,236,672		2,236,672
Beginning balance at Dec. 31, 2019	$ (47,157)		$ 1	3,812	0	(50,970)
Common stock
Conversion of preferred stock to common stock upon closing of the initial public offering (in shares)			21,499,770
Conversion of preferred stock to common stock upon closing of the initial public offering	200,573		$ 3	200,570
Issuance of common stock, net of issuance costs (in shares)			12,174,263
Issuance of common stock, net of issuance costs	212,101		$ 1	212,100
Reclassification of warrants to additional paid-in capital	16			16
Stock-based compensation	1,877			1,877
Net loss	(12,145)					(12,145)
Ending balance (in shares) at Mar. 31, 2020			35,910,705
Ending balance at Mar. 31, 2020	$ 355,265		$ 5	418,375	0	(63,115)
Beginning balance (in shares) at Dec. 31, 2019	64,839,353
Beginning balance at Dec. 31, 2019	$ 200,573
Ending balance (in shares) at Sep. 30, 2020	0
Ending balance at Sep. 30, 2020	$ 0
Beginning balance (in shares) at Dec. 31, 2019	2,236,672		2,236,672
Beginning balance at Dec. 31, 2019	$ (47,157)		$ 1	3,812	0	(50,970)
Common stock
Exercise of common stock options (in shares)	51,076
Change in unrealized (loss) gain on investments	$ 875
Net loss	$ (44,628)
Ending balance (in shares) at Sep. 30, 2020	35,963,447		35,963,447
Ending balance at Sep. 30, 2020	$ 327,345		$ 5	422,063	875	(95,598)
Beginning balance (in shares) at Mar. 31, 2020	0
Beginning balance at Mar. 31, 2020	$ 0
Ending balance (in shares) at Jun. 30, 2020	0
Ending balance at Jun. 30, 2020	$ 0
Beginning balance (in shares) at Mar. 31, 2020			35,910,705
Beginning balance at Mar. 31, 2020	355,265		$ 5	418,375	0	(63,115)
Common stock
Stock-based compensation	1,419			1,419
Change in unrealized (loss) gain on investments	1,012				1,012
Net loss	(14,571)					(14,571)
Ending balance (in shares) at Jun. 30, 2020			35,910,705
Ending balance at Jun. 30, 2020	$ 343,125		$ 5	419,794	1,012	(77,686)
Ending balance (in shares) at Sep. 30, 2020	0
Ending balance at Sep. 30, 2020	$ 0
Common stock
Exercise of common stock options (in shares)			51,076
Exercise of common stock options	270			270
Vesting of restricted stock units (in shares)			1,666
Vesting of restricted stock units	0
Stock-based compensation	1,999			1,999
Change in unrealized (loss) gain on investments	(137)				(137)
Net loss	$ (17,912)					(17,912)
Ending balance (in shares) at Sep. 30, 2020	35,963,447		35,963,447
Ending balance at Sep. 30, 2020	$ 327,345		$ 5	$ 422,063	$ 875	$ (95,598)