CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]
Balance at Dec. 31, 2019	$ 8,330	$ 11	$ 472,765	$ (465,286)	$ 840
Balance, shares at Dec. 31, 2019		10,941,659
Net loss	(29,925)			(29,925)
Issuance of Stock, net of issuance costs	24,701	$ 2	24,699
Issuance of stock, net of issuance costs, shares		2,102,945
Employee stock purchase plan	294		294
Employee stock purchase plan, shares		33,697
Vesting of stock units	(90)		(90)
Vesting of stock units, shares		63,804
Stock-based compensation	4,284		4,284
Balance at Sep. 30, 2020	7,594	$ 13	501,952	(495,211)	840
Balance, shares at Sep. 30, 2020		13,142,105
Balance at Jun. 30, 2020	4,194	$ 13	494,751	(491,410)	840
Balance, shares at Jun. 30, 2020		12,519,713
Net loss	(3,801)			(3,801)
Issuance of Stock, net of issuance costs	4,705		4,705
Issuance of stock, net of issuance costs, shares		602,945
Employee stock purchase plan	107		107
Employee stock purchase plan, shares		17,531
Vesting of stock units, shares		1,916
Stock-based compensation	2,389		2,389
Balance at Sep. 30, 2020	7,594	$ 13	501,952	(495,211)	840
Balance, shares at Sep. 30, 2020		13,142,105
Balance at Dec. 31, 2020	$ 18,541	$ 18	528,362	(510,680)	841
Balance, shares at Dec. 31, 2020	18,139,981	18,139,981
Net loss	$ (38,985)			(38,985)
Issuance of Stock, net of issuance costs	108,414	$ 11	108,403
Issuance of stock, net of issuance costs, shares		10,513,538
Employee stock purchase plan	273		273
Employee stock purchase plan, shares		43,365
Exercise of stock options	11		11
Exercise of stock options, shares		1,078
Vesting of stock units	(145)		(145)
Vesting of stock units, shares		73,302
Stock-based compensation	4,639		4,639
Balance at Sep. 30, 2021	$ 92,748	$ 29	641,543	(549,665)	841
Balance, shares at Sep. 30, 2021	28,771,264	28,771,264
Balance at Jun. 30, 2021	$ 106,865	$ 29	638,965	(532,970)	841
Balance, shares at Jun. 30, 2021		28,754,192
Net loss	(16,695)			(16,695)
Issuance of Stock, net of issuance costs	10		10
Employee stock purchase plan	101		101
Employee stock purchase plan, shares		15,652
Exercise of stock options	1		1
Exercise of stock options, shares		251
Vesting of stock units	(5)		(5)
Vesting of stock units, shares		1,169
Stock-based compensation	2,471		2,471
Balance at Sep. 30, 2021	$ 92,748	$ 29	$ 641,543	$ (549,665)	$ 841
Balance, shares at Sep. 30, 2021	28,771,264	28,771,264