Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED OTHER COMPREHENSIVE (LOSS) GAIN	ACCUMULATED DEFICIT
Beginning balance (in shares) at Dec. 31, 2018		45,478,883
Beginning balance at Dec. 31, 2018	$ 227,806	$ 45	$ 924,180	$ 0	$ (696,419)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and warrants (in shares)		141,245
Issuance of common stock upon exercise of stock options and warrants	1,879		1,879
Issuance of common stock for restricted stock awards, net (in shares)		301,848
Issuance of common stock for restricted stock awards, net	(2,092)	$ 1	(2,093)
Stock-based compensation	12,508		12,508
Other comprehensive loss	0
Net loss	(47,951)				(47,951)
Ending balance (in shares) at Mar. 31, 2019		45,921,976
Ending balance at Mar. 31, 2019	192,150	$ 46	936,474	0	(744,370)
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)	11,684	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 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)