Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Gain (Loss)	Treasury Stock
Balance, shares at Dec. 31, 2014		103,663
Balance, value at Dec. 31, 2014	$ 284,018	$ 104	$ 1,390,619	$ (1,104,252)	$ (63)	$ (2,390)
Stock-based compensation	5,413	$ 0	5,413	0	0	0
Issuance of common stock under Equity Incentive Plans, shares		197
Issuance of common stock under Equity Incentive Plans, value	114	$ 0	114	0	0	0
Repurchase of common stock	(357)	0	0	0	0	(357)
Net loss	(91,432)	0	0	(91,432)	0	0
Unrealized gain on investments	121	0	0	0	121	0
Other	61	$ 0	61	0	0	0
Balance, shares at Sep. 30, 2015		103,860
Balance, value at Sep. 30, 2015	197,938	$ 104	1,396,207	(1,195,684)	58	(2,747)
Balance, shares at Dec. 31, 2015		103,860
Balance, value at Dec. 31, 2015	285,850	$ 104	1,397,646	(1,108,934)	(219)	(2,747)
Stock-based compensation	5,722	$ 0	5,722	0	0	0
Issuance of common stock under Equity Incentive Plans, shares		463
Issuance of common stock under Equity Incentive Plans, value	2,943	$ 0	2,943	0	0	0
Repurchase of common stock	(621)	0	0	0	0	(621)
Net loss	(109,010)	0	0	(109,010)	0	0
Unrealized gain on investments	297	$ 0	0	0	297	0
Balance, shares at Sep. 30, 2016		104,323
Balance, value at Sep. 30, 2016	$ 185,181	$ 104	$ 1,406,311	$ (1,217,944)	$ 78	$ (3,368)