Statements of Stockholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	Junior Series A Preferred Stock	Common Stock	Additional paid-in capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at beginning of period at Dec. 31, 2013	$ 169,720	$ 0	$ 31	$ 352,739	$ (183,050)	$ 0
Balance at beginning of period (in shares) at Dec. 31, 2013		0	31,413
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under employee stock compensation plans and warrants	2,949		$ 1	2,948
Issuance of common stock under employee stock compensation plans and warrants (in shares)			682
Issuance from follow-on public offering, net	55,409		$ 2	55,407
Issuance from follow-on public offering, net (in shares)			1,900
Share-based compensation	13,040			13,040
Excess tax benefit from share-based compensation	4,256			4,256
Net loss	(116,772)				(116,772)
Unrealized gain (loss) on available for sale securities, net of tax	(65)					(65)
Ending balance at Dec. 31, 2014	128,537	$ 0	$ 34	428,390	(299,822)	(65)
Balance at end of period (in shares) at Dec. 31, 2014		0	33,995
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under employee stock compensation plans and warrants	11,473		$ 1	11,472
Issuance of common stock under employee stock compensation plans and warrants (in shares)			1,202
Share-based compensation	24,760			24,760
Excess tax benefit from share-based compensation	1,302			1,302
Net loss	(105,717)				(105,717)
Unrealized gain (loss) on available for sale securities, net of tax	(408)					(408)
Ending balance at Dec. 31, 2015	59,947	$ 0	$ 35	465,924	(405,539)	(473)
Balance at end of period (in shares) at Dec. 31, 2015		0	35,197
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under employee stock compensation plans and warrants	6,934		$ 1	6,933
Issuance of common stock under employee stock compensation plans and warrants (in shares)			536
Share-based compensation	31,660			31,660
Excess tax benefit from share-based compensation	0
Net loss	(193,420)				(193,420)
Unrealized gain (loss) on available for sale securities, net of tax	261					261
Ending balance at Dec. 31, 2016	$ (94,618)	$ 0	$ 36	$ 504,517	$ (598,959)	$ (212)
Balance at end of period (in shares) at Dec. 31, 2016		0	35,733