Condensed Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit
Balances at Dec. 31, 2019	$ (225,139)		$ 1	$ 2,324	$ (227,464)
Temporary Equity Balance, Shares at Dec. 31, 2019		118,766
Temporary Equity Balance at Dec. 31, 2019		$ 193,959
Common Stock Balance, Shares at Dec. 31, 2019			255
Exercise of stock options	11			11
Exercise of stock options, shares			20
Net loss	(9,706)				(9,706)
Balances at Mar. 31, 2020	(234,834)		$ 1	2,335	(237,170)
Temporary Equity Balance, Shares at Mar. 31, 2020		118,766
Temporary Equity Balance at Mar. 31, 2020		$ 193,959
Common Stock Balance, Shares at Mar. 31, 2020			275
Balances at Dec. 31, 2019	(225,139)		$ 1	2,324	(227,464)
Temporary Equity Balance, Shares at Dec. 31, 2019		118,766
Temporary Equity Balance at Dec. 31, 2019		$ 193,959
Common Stock Balance, Shares at Dec. 31, 2019			255
Net loss	(26,817)
Balances at Sep. 30, 2020	(251,776)		$ 1	2,504	(254,281)
Temporary Equity Balance, Shares at Sep. 30, 2020		118,766
Temporary Equity Balance at Sep. 30, 2020		$ 193,959
Common Stock Balance, Shares at Sep. 30, 2020			290
Balances at Mar. 31, 2020	(234,834)		$ 1	2,335	(237,170)
Temporary Equity Balance, Shares at Mar. 31, 2020		118,766
Temporary Equity Balance at Mar. 31, 2020		$ 193,959
Common Stock Balance, Shares at Mar. 31, 2020			275
Stock‑based compensation	55			55
Net loss	(8,266)				(8,266)
Balances at Jun. 30, 2020	(243,045)		$ 1	2,390	(245,436)
Temporary Equity Balance, Shares at Jun. 30, 2020		118,766
Temporary Equity Balance at Jun. 30, 2020		$ 193,959
Common Stock Balance, Shares at Jun. 30, 2020			275
Exercise of stock options	14			14
Exercise of stock options, shares			15
Stock‑based compensation	100			100
Net loss	(8,845)				(8,845)
Balances at Sep. 30, 2020	(251,776)		$ 1	2,504	(254,281)
Temporary Equity Balance, Shares at Sep. 30, 2020		118,766
Temporary Equity Balance at Sep. 30, 2020		$ 193,959
Common Stock Balance, Shares at Sep. 30, 2020			290
Balances at Dec. 31, 2020	41,166		$ 27	299,953	(258,814)
Common Stock Balance, Shares at Dec. 31, 2020			26,562
Exercise of stock options	475			475
Exercise of stock options, shares			223
Stock‑based compensation	1,752			1,752
Net loss	(6,961)				(6,961)
Balances at Mar. 31, 2021	36,432		$ 27	302,180	(265,775)
Common Stock Balance, Shares at Mar. 31, 2021			26,785
Balances at Dec. 31, 2020	$ 41,166		$ 27	299,953	(258,814)
Common Stock Balance, Shares at Dec. 31, 2020			26,562
Exercise of stock options, shares	396,000
Net loss	$ (29,877)
Balances at Sep. 30, 2021	16,033		$ 27	304,697	(288,691)
Common Stock Balance, Shares at Sep. 30, 2021			27,020
Balances at Mar. 31, 2021	36,432		$ 27	302,180	(265,775)
Common Stock Balance, Shares at Mar. 31, 2021			26,785
Exercise of stock options	204			204
Exercise of stock options, shares			164
Stock‑based compensation	539			539
Net loss	(11,402)				(11,402)
Balances at Jun. 30, 2021	25,773		$ 27	302,923	(277,177)
Common Stock Balance, Shares at Jun. 30, 2021			26,949
Issuance of common stock under employee stock purchase plan	328			328
Issuance of common stock under employee stock purchase plan, Shares			43
Exercise of stock options	60			60
Exercise of stock options, shares			28
Stock‑based compensation	1,386			1,386
Net loss	(11,514)				(11,514)
Balances at Sep. 30, 2021	$ 16,033		$ 27	$ 304,697	$ (288,691)
Common Stock Balance, Shares at Sep. 30, 2021			27,020