CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Total	Common Stock	Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2020		128,138,311,000
Beginning balance at Dec. 31, 2020	$ 146,379	$ 1,282	$ 643,269	$ 0	$ (498,172)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs (in shares)		68,170,579,000
Issuance of common stock, net of issuance costs	457,645	$ 682	456,963
Issuance of common stock upon exercise of warrants (in shares)		1,866,758,000
Issuance of common stock upon exercise of warrants	1,121	$ 18	1,103
Non-cash stock-based compensation	1,420		1,420
Issuance of common stock under stock plans, net of taxes ( in shares)		211,172,000
Issuance of common stock under stock plans, net of taxes	(1,825)	$ (2)	(1,823)
Other comprehensive loss	(307)			(307)
Net loss	(28,310)				(28,310)
Ending balance (in shares) at Jun. 30, 2021		197,964,476,000
Ending balance at Jun. 30, 2021	576,123	$ 1,980	1,100,932	(307)	(526,482)
Beginning balance (in shares) at Mar. 31, 2021		198,050,449,000
Beginning balance at Mar. 31, 2021	595,691	$ 1,981	1,101,939	0	(508,229)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock and common stock warrants, net of issuance costs	(45)		(45)
Issuance of common stock upon exercise of warrants (in shares)		3,700,000
Issuance of common stock upon exercise of warrants	4		4
Non-cash stock-based compensation	858		858
Issuance of common stock under stock plans, net of taxes ( in shares)		89,673,000
Issuance of common stock under stock plans, net of taxes	(1,825)	$ (1)	(1,824)
Other comprehensive loss	(307)			(307)
Net loss	(18,253)				(18,253)
Ending balance (in shares) at Jun. 30, 2021		197,964,476,000
Ending balance at Jun. 30, 2021	$ 576,123	$ 1,980	1,100,932	(307)	(526,482)
Beginning balance (in shares) at Dec. 31, 2021	201,988,662	201,988,662,000
Beginning balance at Dec. 31, 2021	$ 547,255	$ 2,020	1,103,224	(614)	(557,375)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock and common stock warrants, net of issue costs (in shares)		33,333,336,000
Issuance of common stock and common stock warrants, net of issuance costs	139,008	$ 333	138,675
Issuance of common stock upon exercise of warrants (in shares)		4,677,000
Issuance of common stock upon exercise of warrants	3		3
Non-cash stock-based compensation	8,264		8,264
Issuance of common stock under stock plans, net of taxes ( in shares)		160,724,000
Issuance of common stock under stock plans, net of taxes	(286)		(286)
Other comprehensive loss	(1,642)			(1,642)
Net loss	$ (28,834)				(28,834)
Ending balance (in shares) at Jun. 30, 2022	235,165,951	235,165,951,000
Ending balance at Jun. 30, 2022	$ 663,768	$ 2,353	1,249,880	(2,256)	(586,209)
Beginning balance (in shares) at Mar. 31, 2022		201,752,722,000
Beginning balance at Mar. 31, 2022	534,435	$ 2,019	1,107,051	(1,587)	(573,048)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock and common stock warrants, net of issue costs (in shares)		33,333,336,000
Issuance of common stock and common stock warrants, net of issuance costs	139,008	$ 333	138,675
Non-cash stock-based compensation	4,220		4,220
Issuance of common stock under stock plans, net of taxes ( in shares)		79,893,000
Issuance of common stock under stock plans, net of taxes	(65)	$ 1	(66)
Other comprehensive loss	(669)			(669)
Net loss	$ (13,161)				(13,161)
Ending balance (in shares) at Jun. 30, 2022	235,165,951	235,165,951,000
Ending balance at Jun. 30, 2022	$ 663,768	$ 2,353	$ 1,249,880	$ (2,256)	$ (586,209)