Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]	Series A Preferred Stock [Member]	Series B Preferred Stock [Member]
Beginning Balance at Dec. 31, 2015	$ 31,696	$ 53	$ 274,891	$ (47)	$ (243,203)	$ 2
Beginning Balance, shares at Dec. 31, 2015		52,730,799				2,093,155
Stock-based compensation	$ 14,931		$ 14,931
Stock-based compensation, Shares	0	0	0	0	0	0	0
Stock option exercises	$ 297		$ 297
Stock option exercises, shares	147,425	147,426
Restricted stock awards, shares		592,065
Common stock issuance upon retirement	$ 2,460	$ 1	2,459
Common stock issuance upon retirement, shares		663,221
Issuance of warrants	49		49
Equity finance costs	40		40
Net income (loss)	(67,138)				$ (67,138)
Ending Balance at Dec. 31, 2016	(17,665)	$ 54	292,667	$ (47)	$ (310,341)	$ 2
Ending Balance, shares at Dec. 31, 2016		54,133,511				2,093,155
Stock-based compensation	$ 14,801		$ 14,801
Stock-based compensation, Shares	0	0	0	0	0	0	0
Stock option exercises	$ 439		$ 439
Stock option exercises, shares	202,519	202,519
Restricted stock awards		$ 2	(2)
Restricted stock awards, shares		1,568,042
Issuance of warrants	$ 6,017		6,017
Net income (loss)	5,285				$ 5,285
Ending Balance at Dec. 31, 2017	8,877	$ 56	313,922	$ (47)	$ (305,056)	$ 2
Ending Balance, shares at Dec. 31, 2017		55,904,072				2,093,155
Stock-based compensation	$ 5,941		$ 5,941
Stock-based compensation, Shares	0	0	0	0	0	0	0
Stock option exercises	$ 670		$ 670
Stock option exercises, shares	350,441	350,441
Restricted stock awards		$ 2	(2)
Restricted stock awards, shares		1,733,731
Common stock issuance upon retirement		$ 2	(2)
Common stock issuance upon retirement, shares	2,119,925	2,249,925
Series B issuance, net of issuance costs	$ 47,986		47,986
Series B issuance, net of issuance costs, shares							5,000
Series B conversion to Common Stock		$ 11	(11)
Series B conversion to Common Stock, shares		10,555,556					(1,900)
Series B beneficial conversion feature	(12,500)		12,500		$ (12,500)
Cumulative effect of accounting change	135				135
Net income (loss)	(33,867)				(33,867)
Ending Balance at Dec. 31, 2018	$ 29,742	$ 71	$ 381,004	$ (47)	$ (351,288)	$ 2
Ending Balance, shares at Dec. 31, 2018		70,793,725				2,093,155	3,100