Condensed Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME	ACCUMULATED DEFICIT
Beginning balance (in shares) at Dec. 31, 2019		46,464,669
Beginning balance at Dec. 31, 2019	$ 166,950	$ 46	$ 1,062,996	$ (92)	$ (896,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and warrants (in shares)		5,811
Issuance of common stock upon exercise of stock options and warrants	44		44
Issuance of common stock for restricted stock awards, net (in shares)		5,705
Issuance of common stock for restricted stock awards, net	(1,466)		(1,466)
Stock-based compensation	10,838		10,838
Other comprehensive income (loss)	(28)			(28)
Net loss	(49,129)				(49,129)
Ending balance (in shares) at Mar. 31, 2020		46,476,185
Ending balance at Mar. 31, 2020	127,209	$ 46	1,072,412	(120)	(945,129)
Beginning balance (in shares) at Dec. 31, 2019		46,464,669
Beginning balance at Dec. 31, 2019	166,950	$ 46	1,062,996	(92)	(896,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss)	209
Net loss	(97,316)
Ending balance (in shares) at Jun. 30, 2020		46,513,349
Ending balance at Jun. 30, 2020	89,812	$ 47	1,082,964	117	(993,316)
Beginning balance (in shares) at Mar. 31, 2020		46,476,185
Beginning balance at Mar. 31, 2020	127,209	$ 46	1,072,412	(120)	(945,129)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock purchase rights (in shares)		23,494
Issuance of common stock upon exercise of stock purchase rights	295		295
Issuance of common stock upon exercise of stock options and warrants (in shares)		31,615
Issuance of common stock upon exercise of stock options and warrants	119	$ 1	118
Issuance of common stock for restricted stock awards, net (in shares)		(17,945)
Issuance of common stock for restricted stock awards, net	(150)		(150)
Stock-based compensation	10,289		10,289
Other comprehensive income (loss)	237			237
Net loss	(48,187)				(48,187)
Ending balance (in shares) at Jun. 30, 2020		46,513,349
Ending balance at Jun. 30, 2020	89,812	$ 47	1,082,964	117	(993,316)
Beginning balance (in shares) at Dec. 31, 2020		46,821,644
Beginning balance at Dec. 31, 2020	23,968	$ 47	1,103,074	(52)	(1,079,101)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and warrants (in shares)		62,016
Issuance of common stock upon exercise of stock options and warrants	26		26
Issuance of common stock for restricted stock awards, net (in shares)		10,162
Issuance of common stock for restricted stock awards, net	(1,127)		(1,127)
Stock-based compensation	8,741		8,741
Other comprehensive income (loss)	(12)			(12)
Net loss	(41,964)				(41,964)
Ending balance (in shares) at Mar. 31, 2021		46,893,822
Ending balance at Mar. 31, 2021	(10,368)	$ 47	1,110,714	(64)	(1,121,065)
Beginning balance (in shares) at Dec. 31, 2020		46,821,644
Beginning balance at Dec. 31, 2020	$ 23,968	$ 47	1,103,074	(52)	(1,079,101)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and warrants (in shares)	90,930
Other comprehensive income (loss)	$ (9)
Net loss	(80,652)
Ending balance (in shares) at Jun. 30, 2021		46,994,403
Ending balance at Jun. 30, 2021	(39,614)	$ 47	1,120,153	(61)	(1,159,753)
Beginning balance (in shares) at Mar. 31, 2021		46,893,822
Beginning balance at Mar. 31, 2021	(10,368)	$ 47	1,110,714	(64)	(1,121,065)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock purchase rights (in shares)		89,555
Issuance of common stock upon exercise of stock purchase rights	998		998
Issuance of common stock upon exercise of stock options and warrants (in shares)		18,426
Issuance of common stock upon exercise of stock options and warrants	91		91
Issuance of common stock for restricted stock awards, net (in shares)		(7,400)
Issuance of common stock for restricted stock awards, net	(13)		(13)
Stock-based compensation	8,363		8,363
Other comprehensive income (loss)	3			3
Net loss	(38,688)				(38,688)
Ending balance (in shares) at Jun. 30, 2021		46,994,403
Ending balance at Jun. 30, 2021	$ (39,614)	$ 47	$ 1,120,153	$ (61)	$ (1,159,753)