Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED OTHER COMPREHENSIVE LOSS	ACCUMULATED DEFICIT
Beginning balance (in shares) at Dec. 31, 2017		36,947,637
Beginning balance at Dec. 31, 2017	$ 135,599	$ 37	$ 597,318	$ (28)	$ (461,728)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of commissions and expenses (in shares)		2,313,824
Issuance of common stock, net of commissions and expenses	136,375	$ 2	136,373
Issuance of common stock upon exercise of stock options and warrants (in shares)		28,654
Issuance of common stock upon exercise of stock options and warrants	95		95
Issuance of common stock for restricted stock awards, net (in shares)		212,995
Issuance of common stock for restricted stock awards, net	(1,595)	$ (1)	(1,596)
Stock-based compensation	8,762		8,762
Other comprehensive loss	(129)			(129)
Net loss	(40,699)				(40,699)
Ending balance (in shares) at Mar. 31, 2018		39,503,110
Ending balance at Mar. 31, 2018	236,271	$ 40	740,952	(157)	(504,564)
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)	111,242	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
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)