Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Contributed Capital	Accumulated Deficit	Treasury stock	Accumulated Other Comprehensive Income (Loss)
Beginning Balance, amount at Dec. 31, 2015	$ 133,018	$ 51	$ 243,894	$ (110,915)	$ 0	$ (12)
Beginning Balance (shares) at Dec. 31, 2015		51,191,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(66,374)			(66,374)
Exercise of options, warrants and awards	1,497	$ 1	1,496
Exercise of options, warrants and awards (shares)		314,000
Issuance of common stock under employee purchase plan	226		226
Issuance of common stock under employee purchase plan (shares)		11,000
Short swing profits (net of costs)	866		866
Unrealized loss on available-for-sale securities	(64)					(64)
Foreign currency translation adjustment	(128)					(128)
Equity-based compensation	8,775		8,775
Ending Balance, amount at Dec. 31, 2016	77,816	$ 52	255,257	(177,289)	0	(204)
Ending Balance (shares) at Dec. 31, 2016		51,516,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(64,028)			(64,028)
Issuance of common stock	83,224	$ 3	83,221
Issuance of common stock (shares)		3,085,000
Exercise of options, warrants and awards	$ 6,606	$ 1	6,605
Exercise of options, warrants and awards (shares)	656,846	1,045,000
Issuance of common stock under employee purchase plan	$ 597		597
Issuance of common stock under employee purchase plan (shares)		28,000
Unrealized loss on available-for-sale securities	(117)					(117)
Foreign currency translation adjustment	321					321
Equity-based compensation	14,940		14,940
Ending Balance, amount at Dec. 31, 2017	118,704	$ 56	360,620	(241,972)	0	0
Ending Balance (shares) at Dec. 31, 2017		55,674,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of accounting change	(655)			(655)
Net loss	(88,326)			(88,326)
Exercise of options, warrants and awards	$ 3,749	$ 0	3,749
Exercise of options, warrants and awards (shares)	357,373	382,000
Issuance of common stock under employee purchase plan	$ 583		583
Issuance of common stock under employee purchase plan (shares)		35,000
Unrealized loss on available-for-sale securities	23					23
Foreign currency translation adjustment	(172)					(172)
Repurchase of common stock under Prepaid Forward contract	$ (45,069)	$ (2)			(45,067)
Repurchase of common stock under Prepaid Forward contract (shares)	(1,858,500)	(1,859,000)
Issuance of convertible note	$ 53,283		53,283
Equity-based compensation	14,650		14,650
Ending Balance, amount at Dec. 31, 2018	$ 57,375	$ 54	$ 432,885	$ (330,348)	$ (45,067)	$ (149)
Ending Balance (shares) at Dec. 31, 2018		54,232,000