Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Contributed Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning Balance, amount at Dec. 31, 2014	$ 65,991	$ 45	$ 131,356	$ (65,417)	$ 7
Beginning Balance (shares) at Dec. 31, 2014		44,640,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(45,498)			(45,498)
Issuance of common stock	103,351	$ 6	103,345
Issuance of common stock (shares)		6,426,000
Exercise of options and warrants	805		805
Exercise of options and warrants (shares)		125,000
Unrealized loss on available-for-sale securities	(20)				(20)
Foreign currency translation adjustment	1				1
Equity-based compensation	8,388		8,388
Ending Balance, amount at Dec. 31, 2015	133,018	$ 51	243,894	(110,915)	(12)
Ending 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 and warrants	$ 1,497	$ 1	1,496
Exercise of options and warrants (shares)	158,743	314,000
Short swing profits (net of costs)	$ 866		866
Issuance of common stock under employee purchase plan	226		226
Issuance of common stock under employee purchase plan (shares)		11,000
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)	(204)
Ending Balance (shares) at Dec. 31, 2016		51,516,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of accounting change for forfeitures	(655)			(655)
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 and warrants	$ 6,606	$ 1	6,605
Exercise of options and warrants (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
Ending Balance (shares) at Dec. 31, 2017		55,674,000