CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' DEFICIT (unaudited) - USD ($) $ in Thousands	Total		Convertible Preferred Stock	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit
Convertible Preferred Stock Beginning balance, Shares at Dec. 31, 2019			17,031,887
Convertible Preferred Stock Beginning balance at Dec. 31, 2019			$ 281,342
Beginning balance, Shares at Dec. 31, 2019				1,188,815
Beginning balance at Dec. 31, 2019	$ (208,914)			$ 2	$ (51)	$ 8,015	$ (216,880)
Exercise of stock options	13					13
Exercise of stock options, Shares				2,637
Stock-based compensation	268					268
Net loss	(13,001)						(13,001)
Convertible Preferred Stock Ending balance, Shares at Mar. 31, 2020			17,031,887
Convertible Preferred Stock Ending balance at Mar. 31, 2020			$ 281,342
Ending balance, Shares at Mar. 31, 2020				1,191,452
Ending balance at Mar. 31, 2020	(221,634)			$ 2	(51)	8,296	(229,881)
Convertible Preferred Stock Beginning balance, Shares at Dec. 31, 2019			17,031,887
Convertible Preferred Stock Beginning balance at Dec. 31, 2019			$ 281,342
Beginning balance, Shares at Dec. 31, 2019				1,188,815
Beginning balance at Dec. 31, 2019	(208,914)			$ 2	(51)	8,015	(216,880)
Net loss	(34,138)
Convertible Preferred Stock Ending balance, Shares at Sep. 30, 2020			17,031,887
Convertible Preferred Stock Ending balance at Sep. 30, 2020			$ 281,342
Ending balance, Shares at Sep. 30, 2020				1,199,723
Ending balance at Sep. 30, 2020	(241,836)			$ 2	(51)	9,231	(251,018)
Convertible Preferred Stock Beginning balance, Shares at Mar. 31, 2020			17,031,887
Convertible Preferred Stock Beginning balance at Mar. 31, 2020			$ 281,342
Beginning balance, Shares at Mar. 31, 2020				1,191,452
Beginning balance at Mar. 31, 2020	(221,634)			$ 2	(51)	8,296	(229,881)
Exercise of stock options	15					15
Exercise of stock options, Shares				5,298
Stock-based compensation	442					442
Net loss	(10,544)						(10,544)
Convertible Preferred Stock Ending balance, Shares at Jun. 30, 2020			17,031,887
Convertible Preferred Stock Ending balance at Jun. 30, 2020			$ 281,342
Ending balance, Shares at Jun. 30, 2020				1,196,750
Ending balance at Jun. 30, 2020	(231,721)			$ 2	(51)	8,753	(240,425)
Exercise of stock options	13					13
Exercise of stock options, Shares				2,973
Stock-based compensation	465					465
Net loss	(10,593)						(10,593)
Convertible Preferred Stock Ending balance, Shares at Sep. 30, 2020			17,031,887
Convertible Preferred Stock Ending balance at Sep. 30, 2020			$ 281,342
Ending balance, Shares at Sep. 30, 2020				1,199,723
Ending balance at Sep. 30, 2020	$ (241,836)			$ 2	(51)	9,231	(251,018)
Convertible Preferred Stock Beginning balance, Shares at Dec. 31, 2020	17,031,887		17,031,887
Convertible Preferred Stock Beginning balance at Dec. 31, 2020	$ 281,342	[1]	$ 281,342
Beginning balance, Shares at Dec. 31, 2020				1,200,335
Beginning balance at Dec. 31, 2020	(253,891)			$ 2	(51)	9,703	(263,545)
Exercise of stock options	33					33
Exercise of stock options, Shares				12,797
Stock-based compensation	494					494
Net loss	(10,906)						(10,906)
Convertible Preferred Stock Ending balance, Shares at Mar. 31, 2021			17,031,887
Convertible Preferred Stock Ending balance at Mar. 31, 2021			$ 281,342
Ending balance, Shares at Mar. 31, 2021				1,213,132
Ending balance at Mar. 31, 2021	$ (264,270)			$ 2	(51)	10,230	(274,451)
Convertible Preferred Stock Beginning balance, Shares at Dec. 31, 2020	17,031,887		17,031,887
Convertible Preferred Stock Beginning balance at Dec. 31, 2020	$ 281,342	[1]	$ 281,342
Beginning balance, Shares at Dec. 31, 2020				1,200,335
Beginning balance at Dec. 31, 2020	$ (253,891)			$ 2	(51)	9,703	(263,545)
Exercise of stock options, Shares	58,290
Net loss	$ (34,788)
Convertible Preferred Stock Ending balance, Shares at Sep. 30, 2021	17,031,887		17,031,887
Convertible Preferred Stock Ending balance at Sep. 30, 2021	$ 281,342	[1]	$ 281,342
Ending balance, Shares at Sep. 30, 2021				1,258,945
Ending balance at Sep. 30, 2021	(287,056)			$ 2	(51)	11,326	(298,333)
Convertible Preferred Stock Beginning balance, Shares at Mar. 31, 2021			17,031,887
Convertible Preferred Stock Beginning balance at Mar. 31, 2021			$ 281,342
Beginning balance, Shares at Mar. 31, 2021				1,213,132
Beginning balance at Mar. 31, 2021	(264,270)			$ 2	(51)	10,230	(274,451)
Exercise of stock options	56					56
Exercise of stock options, Shares				10,214
Stock-based compensation	413					413
Net loss	(11,149)						(11,149)
Convertible Preferred Stock Ending balance, Shares at Jun. 30, 2021			17,031,887
Convertible Preferred Stock Ending balance at Jun. 30, 2021			$ 281,342
Ending balance, Shares at Jun. 30, 2021				1,223,346
Ending balance at Jun. 30, 2021	(274,950)			$ 2	(51)	10,699	(285,600)
Exercise of stock options	86					86
Exercise of stock options, Shares				35,599
Stock-based compensation	541					541
Net loss	$ (12,733)						(12,733)
Convertible Preferred Stock Ending balance, Shares at Sep. 30, 2021	17,031,887		17,031,887
Convertible Preferred Stock Ending balance at Sep. 30, 2021	$ 281,342	[1]	$ 281,342
Ending balance, Shares at Sep. 30, 2021				1,258,945
Ending balance at Sep. 30, 2021	$ (287,056)			$ 2	$ (51)	$ 11,326	$ (298,333)

[1] The carrying value reflects the gross proceeds received from the sale of the preferred stock less issuance costs and the fair value at issuance of preferred stock warrants classified as a liability.