CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Paid-In Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit	Treasury Stock	Total
Balance at Dec. 31, 2017		$ 297,278	$ 287	$ (256,190)	$ (258)	$ 41,117
Balance, shares at Dec. 31, 2017	555,806
Net loss				(23,876)		(23,876)
Common stock and common stock purchase warrants issued, net of issuance costs	$ 1	11,422				11,423
Common stock and common stock purchase warrants issued, net of issuance costs(in shares)	387,194
Stock compensation expense and related share issuances, net of shares withheld for payment of taxes		162				162
Stock compensation expense and related share issuances, net of shares withheld for payment of taxes, shares	419
Minimum withholding taxes on net share settlements of equity awards		(5)				(5)
Unrealized holding loss on marketable securities			(1,056)			(1,056)
Transfer to realized loss upon sale of available-for-sale securities			93			93
Balance at Jun. 30, 2018	$ 1	308,857	(676)	(280,066)	(258)	27,858
Balance, shares at Jun. 30, 2018	943,419
Balance at Mar. 31, 2018		298,010	(650)	(259,609)	(258)	37,493
Balance, shares at Mar. 31, 2018	576,628
Net loss				(20,457)		(20,457)
Common stock and common stock purchase warrants issued, net of issuance costs	$ 1	10,770				10,771
Common stock and common stock purchase warrants issued, net of issuance costs(in shares)	366,392
Stock compensation expense and related share issuances, net of shares withheld for payment of taxes		82				82
Stock compensation expense and related share issuances, net of shares withheld for payment of taxes, shares	399
Minimum withholding taxes on net share settlements of equity awards		(5)		(5)
Unrealized holding loss on marketable securities			(119)			(119)
Transfer to realized loss upon sale of available-for-sale securities			93			93
Balance at Jun. 30, 2018	$ 1	308,857	(676)	(280,066)	(258)	27,858
Balance, shares at Jun. 30, 2018	943,419
Balance at Dec. 31, 2018	$ 1	313,012	(90)	(291,874)	(258)	20,791
Balance, shares at Dec. 31, 2018	1,436,555
Net loss				(5,949)		(5,949)
Common stock and common stock purchase warrants issued, net of issuance costs	$ 1	1,153				1,154
Common stock and common stock purchase warrants issued, net of issuance costs(in shares)	221,263
Stock compensation expense and related share issuances, net of shares withheld for payment of taxes		15				15
Stock compensation expense and related share issuances, net of shares withheld for payment of taxes, shares	393
Minimum withholding taxes on net share settlements of equity awards		(1)				(1)
Transfer to realized loss upon sale of available-for-sale securities			90			90
Balance at Jun. 30, 2019	$ 2	314,179	0	(297,823)	(258)	16,100
Balance, shares at Jun. 30, 2019	1,658,211
Balance at Mar. 31, 2019	$ 1	313,435	0	(295,048)	(258)	18,130
Balance, shares at Mar. 31, 2019	1,494,153
Net loss				(2,775)		(2,775)
Common stock and common stock purchase warrants issued, net of issuance costs	$ 1	738				739
Common stock and common stock purchase warrants issued, net of issuance costs(in shares)	164,058
Stock compensation expense and related share issuances, net of shares withheld for payment of taxes		7				7
Minimum withholding taxes on net share settlements of equity awards		(1)				(1)
Balance at Jun. 30, 2019	$ 2	$ 314,179	$ 0	$ (297,823)	$ (258)	$ 16,100
Balance, shares at Jun. 30, 2019	1,658,211