Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid in Capital	Accumulated Other Comprehensive (Loss) Gain	Accumulated Deficit
Beginning balance at Dec. 31, 2012	$ 154,372	$ 66	$ 873,981	$ (2)	$ (719,673)
Beginning balance (in shares) at Dec. 31, 2012		66,447
Net income (loss)	(46,090)	$ 0	0	0	(46,090)
Unrealized gains (losses) on investments	7	0	0	7	0
Share-based compensation	6,819	0	6,819	0	0
Issuance of common stock for option exercises	$ 5,302	$ 1	5,301	0	0
Issuance of common stock for option exercises (in shares)	904	904
Ending balance at Dec. 31, 2013	$ 120,410	$ 67	886,101	5	(765,763)
Ending balance (in shares) at Dec. 31, 2013		67,351
Net income (loss)	(60,542)	$ 0	0	0	(60,542)
Unrealized gains (losses) on investments	(282)	0	0	(282)	0
Share-based compensation	10,382	0	10,382	0	0
Issuance of common stock for restricted share units vested	0	$ 0	0	0	0
Issuance of common stock for restricted share units vested (in shares)		93
Issuance of common stock for option exercises	$ 5,560	$ 1	5,559	0	0
Issuance of common stock for option exercises (in shares)	1,135	1,022
Issuance of common stock, net of offering costs	$ 133,171	$ 8	133,163	0	0
Issuance of common stock, net of offering costs (in shares)		8,000
Ending balance at Dec. 31, 2014	208,699	$ 76	1,035,205	(277)	(826,305)
Ending balance (in shares) at Dec. 31, 2014		76,466
Net income (loss)	(88,929)	$ 0	0	0	(88,929)
Unrealized gains (losses) on investments	(700)	0	0	(700)	0
Share-based compensation	28,392	0	28,392	0	0
Issuance of common stock for restricted share units vested	1	$ 1	0	0	0
Issuance of common stock for restricted share units vested (in shares)		503
Issuance of common stock for option exercises	$ 6,304	$ 1	6,303	0	0
Issuance of common stock for option exercises (in shares)	1,315	1,308
Issuance of common stock, net of offering costs	$ 270,687	$ 8	270,679	0	0
Issuance of common stock, net of offering costs (in shares)		7,986
Ending balance at Dec. 31, 2015	$ 424,454	$ 86	$ 1,340,579	$ (977)	$ (915,234)
Ending balance (in shares) at Dec. 31, 2015		86,263