Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ (41,119)			$ 6,095	$ (7)	$ (47,207)
Beginning balance, Shares at Dec. 31, 2019		7,597
Beginning balance at Dec. 31, 2019		$ 19,835
Beginning balance, Shares at Dec. 31, 2019			4,502
Issuance of common stock upon exercise of stock options	1			1
Issuance of common stock upon exercise of stock options, Shares			4
Repurchase of unvested restricted stock awards			(40)
Issuance of Series A redeemable convertible preferred stock		$ 14,479
Issuance of Series A redeemable, Shares		4,237
Exercise of redeemable convertible preferred stock tranche liability		$ 9,723
Stock-based compensation expense	100			100
Other comprehensive income (loss)	(215)				(215)
Net loss	(5,149)					(5,149)
Ending balance at Mar. 31, 2020	(46,382)			6,196	(222)	(52,356)
Ending balance, Shares at Mar. 31, 2020		11,834
Ending balance at Mar. 31, 2020		$ 44,037
Ending balance, Shares at Mar. 31, 2020			4,466
Beginning balance at Dec. 31, 2019	(41,119)			6,095	(7)	(47,207)
Beginning balance, Shares at Dec. 31, 2019		7,597
Beginning balance at Dec. 31, 2019		$ 19,835
Beginning balance, Shares at Dec. 31, 2019			4,502
Net loss	(31,709)
Ending balance at Sep. 30, 2020	(72,192)	$ 44,037		6,810	(86)	(78,916)
Ending balance, Shares at Sep. 30, 2020		11,834
Ending balance, Shares at Sep. 30, 2020			4,456
Beginning balance at Mar. 31, 2020	(46,382)			6,196	(222)	(52,356)
Beginning balance, Shares at Mar. 31, 2020		11,834
Beginning balance at Mar. 31, 2020		$ 44,037
Beginning balance, Shares at Mar. 31, 2020			4,466
Stock-based compensation expense	299			299
Other comprehensive income (loss)	49				49
Net loss	(7,743)					(7,743)
Ending balance at Jun. 30, 2020	(53,777)	$ 44,037		6,495	(173)	(60,099)
Ending balance, Shares at Jun. 30, 2020		11,834
Ending balance, Shares at Jun. 30, 2020			4,466
Repurchase of unvested restricted stock awards			(10)
Stock-based compensation expense	315			315
Other comprehensive income (loss)	87				87
Net loss	(18,817)					(18,817)
Ending balance at Sep. 30, 2020	(72,192)	$ 44,037		6,810	(86)	(78,916)
Ending balance, Shares at Sep. 30, 2020		11,834
Ending balance, Shares at Sep. 30, 2020			4,456
Beginning balance at Dec. 31, 2020	$ 334,622		$ 4	463,436	11	(128,829)
Beginning balance, Shares at Dec. 31, 2020	42,282		42,282
Issuance of common stock upon exercise of stock options and warrants and vesting of restricted stock units	$ 580			580
Issuance of common stock upon exercise of stock options and warrants and vesting of restricted stock units, shares			100
Stock-based compensation expense	2,478			2,478
Other comprehensive income (loss)	54				54
Net loss	(37,215)					(37,215)
Ending balance at Mar. 31, 2021	300,519		$ 4	466,494	65	(166,044)
Ending balance, Shares at Mar. 31, 2021			42,382
Beginning balance at Dec. 31, 2020	$ 334,622		$ 4	463,436	11	(128,829)
Beginning balance, Shares at Dec. 31, 2020	42,282		42,282
Issuance of common stock upon exercise of stock options, Shares	281
Net loss	$ (110,482)
Ending balance at Sep. 30, 2021	$ 269,780		$ 4	508,714	373	(239,311)
Ending balance, Shares at Sep. 30, 2021	44,830		44,830
Beginning balance at Mar. 31, 2021	$ 300,519		$ 4	466,494	65	(166,044)
Beginning balance, Shares at Mar. 31, 2021			42,382
Issuance of common stock upon exercise of stock options and warrants, issuance of common stock under Employee Stock Purchase Plan, and vesting of restricted stock units	1,188			1,188
Issuance of common stock upon exercise of stock options and warrants, issuance of common stock under Employee Stock Purchase Plan, and vesting of restricted stock units, shares			178
Issuance of common stock under the at-the-market sales agreement,net of offering costs	33,891			33,891
Issuance of common stock under the at-the-market sales agreement net of offering costs, shares			2,216
Stock-based compensation expense	3,595			3,595
Other comprehensive income (loss)	107				107
Net loss	(42,571)					(42,571)
Ending balance at Jun. 30, 2021	296,729		$ 4	505,168	172	(208,615)
Ending balance, Shares at Jun. 30, 2021			44,776
Issuance of common stock upon exercise of stock options and warrants and vesting of restricted stock units	259			259
Issuance of common stock upon exercise of stock options and warrants and vesting of restricted stock units, shares			54
Stock-based compensation expense	3,287			3,287
Other comprehensive income (loss)	201				201
Net loss	(30,696)					(30,696)
Ending balance at Sep. 30, 2021	$ 269,780		$ 4	$ 508,714	$ 373	$ (239,311)
Ending balance, Shares at Sep. 30, 2021	44,830		44,830