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]
Beginning Balance at Dec. 31, 2014	$ 54,396	$ 52	$ 259,920	$ (47)	$ (205,531)	$ 2
Beginning Balance, shares at Dec. 31, 2014		51,603,070				2,139,000
Stock-based compensation	14,249		14,249
Stock option exercise	$ 755		755
Stock option exercise, shares	235,480	223,923
Restricted stock awards	$ 1	$ 1
Restricted stock awards, shares		857,677
Warrant exercises	1		1
Warrant exercises, shares		284
Short swing profit return / Issuance of warrants	6		6
Conversion of preferred shares to common shares	0	$ 0	0	0	0	$ 0
Conversion of preferred shares to common shares, shares		45,845				(45,845)
Equity financing costs	(40)		(40)
Net income (loss)	(37,672)				(37,672)
Ending Balance at Dec. 31, 2015	31,696	$ 53	274,891	(47)	(243,203)	$ 2
Ending Balance, shares at Dec. 31, 2015		52,730,799				2,093,155
Stock-based compensation	14,931		14,931
Stock option exercise	$ 297		297
Stock option exercise, 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
Short swing profit return / Issuance of warrants	49		49
Equity financing 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 option exercise	$ 439		439
Stock option exercise, shares	202,519	202,519
Restricted stock awards		$ 2	(2)
Restricted stock awards, shares		1,568,042
Short swing profit return / 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