Condensed Consolidated Statements of Stockholders' Equity / (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Purchase Agreement	Purchase Agreement Common Stock	Purchase Agreement Additional Paid-in Capital	Second Purchase Agreement Common Stock
Beginning balance at Dec. 31, 2017	$ (4,058)	$ 3	$ 0	$ (24)	$ 469,884	$ (473,921)
Beginning balance (shares) at Dec. 31, 2017		2,750,000	350,118	392
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,029				1,029
Restricted stock vested (shares)			1,500
Issuance of common stock as a result of Employee Stock Purchase Program	137				137
Issuance of common stock as a result of Employee Stock Purchase Program (shares)			2,755
Net loss	(11,574)					(11,574)
Ending balance at Mar. 31, 2018	(14,487)	$ 3	$ 0	$ (24)	471,050	(485,516)
Ending balance (shares) at Mar. 31, 2018		2,750,000	354,373	392
Beginning balance at Dec. 31, 2017	(4,058)	$ 3	$ 0	$ (24)	469,884	(473,921)
Beginning balance (shares) at Dec. 31, 2017		2,750,000	350,118	392
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(22,534)
Ending balance at Jun. 30, 2018	2,808	$ 3	$ 1	$ (24)	499,304	(496,476)
Ending balance (shares) at Jun. 30, 2018		2,750,000	1,234,687	392.000
Beginning balance at Mar. 31, 2018	(14,487)	$ 3	$ 0	$ (24)	471,050	(485,516)
Beginning balance (shares) at Mar. 31, 2018		2,750,000	354,373	392
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,011				1,011
Issuance of common stock through sales agreement, net of fees	24,359		$ 1		24,358
Stock issued during period (shares)			765,000
Issuance of common stock as a result of Purchase Agreements, net of fees							$ 2,885		$ 2,885
Issuance of common stock as a result of Purchase Agreements, net of fees (shares)								102,121		13,193
Net loss	(10,960)					(10,960)
Ending balance at Jun. 30, 2018	2,808	$ 3	$ 1	$ (24)	499,304	(496,476)
Ending balance (shares) at Jun. 30, 2018		2,750,000	1,234,687	392.000
Beginning balance at Dec. 31, 2018	14,289	$ 3	$ 5	$ (24)	534,176	(519,871)
Beginning balance (shares) at Dec. 31, 2018		2,750,000	4,997,151.55	392
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,069				1,069
Issuance of common stock through sales agreement, net of fees	773				773
Stock issued during period (shares)			109,117
Issuance of common stock with exercise of Series B warrants	20				20
Issuance of common stock through exercise of Series B Warrants, net of fees (shares)			2,096
Net loss	(14,684)					(14,684)
Ending balance at Mar. 31, 2019	1,467	$ 3	$ 5	$ (24)	536,038	(534,555)
Ending balance (shares) at Mar. 31, 2019		2,750,000	5,108,365	392
Beginning balance at Dec. 31, 2018	14,289	$ 3	$ 5	$ (24)	534,176	(519,871)
Beginning balance (shares) at Dec. 31, 2018		2,750,000	4,997,151.55	392
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(28,703)
Ending balance at Jun. 30, 2019	(7,908)	$ 3	$ 6	$ (24)	540,681	(548,574)
Ending balance (shares) at Jun. 30, 2019		2,750,000	5,988,224	392
Beginning balance at Mar. 31, 2019	1,467	$ 3	$ 5	$ (24)	536,038	(534,555)
Beginning balance (shares) at Mar. 31, 2019		2,750,000	5,108,365	392
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	813				813
Issuance of common stock through sales agreement, net of fees	3,831		$ 1		3,830
Stock issued during period (shares)			879,859
Net loss	(14,019)					(14,019)
Ending balance at Jun. 30, 2019	$ (7,908)	$ 3	$ 6	$ (24)	$ 540,681	$ (548,574)
Ending balance (shares) at Jun. 30, 2019		2,750,000	5,988,224	392