CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative-effect Adjustment from Adoption of ASU 2020-06	Common Stock	Additional Paid-In-Capital	Additional Paid-In-Capital Cumulative-effect Adjustment from Adoption of ASU 2020-06	Accumulated Deficit	Accumulated Deficit Cumulative-effect Adjustment from Adoption of ASU 2020-06	Accumulated Other Comprehensive Income
Beginning balance at Dec. 31, 2019	$ 125,239		$ 22	$ 387,926		$ (262,743)		$ 34
Beginning balance, shares at Dec. 31, 2019			22,217
Issuance of common stock	2,014		$ 1	2,013
Issuance of common stock, shares			460
Stock-based compensation	5,221			5,221
Net loss	(4,326)					(4,326)
Other comprehensive income	71							71
Ending balance at Mar. 31, 2020	128,219		$ 23	395,160		(267,069)		105
Ending balance, shares at Mar. 31, 2020			22,677
Beginning balance at Dec. 31, 2019	125,239		$ 22	387,926		(262,743)		34
Beginning balance, shares at Dec. 31, 2019			22,217
Net loss	(36,206)
Other comprehensive income	(22)
Ending balance at Sep. 30, 2020	109,428		$ 23	408,342		(298,949)		12
Ending balance, shares at Sep. 30, 2020			23,001
Beginning balance at Mar. 31, 2020	128,219		$ 23	395,160		(267,069)		105
Beginning balance, shares at Mar. 31, 2020			22,677
Issuance of common stock	1,015			1,015
Issuance of common stock, shares			109
Stock-based compensation	4,597			4,597
Net loss	(17,534)					(17,534)
Other comprehensive income	(47)							(47)
Ending balance at Jun. 30, 2020	116,250		$ 23	400,772		(284,603)		58
Ending balance, shares at Jun. 30, 2020			22,786
Issuance of common stock	1,887			1,887
Issuance of common stock, shares			215
Stock-based compensation	5,683			5,683
Net loss	(14,346)					(14,346)
Other comprehensive income	(46)							(46)
Ending balance at Sep. 30, 2020	109,428		$ 23	408,342		(298,949)		12
Ending balance, shares at Sep. 30, 2020			23,001
Beginning balance at Dec. 31, 2020	109,119	$ (29,301)	$ 23	423,759	$ (32,743)	(314,666)	$ 3,442	3
Beginning balance, shares at Dec. 31, 2020			23,350
Issuance of common stock	8,524		$ 1	8,523
Issuance of common stock, shares			702
Stock-based compensation	7,449			7,449
Net loss	(9,416)					(9,416)
Ending balance at Mar. 31, 2021	86,375		$ 24	406,988		(320,640)		3
Ending balance, shares at Mar. 31, 2021			24,052
Beginning balance at Dec. 31, 2020	109,119	$ (29,301)	$ 23	423,759	$ (32,743)	(314,666)	$ 3,442	3
Beginning balance, shares at Dec. 31, 2020			23,350
Net loss	(31,246)
Other comprehensive income	(6)
Ending balance at Sep. 30, 2021	89,278		$ 24	431,727		(342,470)		(3)
Ending balance, shares at Sep. 30, 2021			24,409
Beginning balance at Mar. 31, 2021	86,375		$ 24	406,988		(320,640)		3
Beginning balance, shares at Mar. 31, 2021			24,052
Issuance of common stock	719			719
Issuance of common stock, shares			202
Stock-based compensation	10,582			10,582
Net loss	(8,906)					(8,906)
Other comprehensive income	1							1
Ending balance at Jun. 30, 2021	88,771		$ 24	418,289		(329,546)		4
Ending balance, shares at Jun. 30, 2021			24,254
Issuance of common stock	2,518			2,518
Issuance of common stock, shares			155
Stock-based compensation	10,920			10,920
Net loss	(12,924)					(12,924)
Other comprehensive income	(7)							(7)
Ending balance at Sep. 30, 2021	$ 89,278		$ 24	$ 431,727		$ (342,470)		$ (3)
Ending balance, shares at Sep. 30, 2021			24,409