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	3,741	$ 0	3,741	0	0	0
Issuance of common stock under Equity Incentive Plans, shares		188
Issuance of common stock under Equity Incentive Plans, value	0	$ 0	0	0	0	0
Repurchase of common stock	(357)	0	0	0	0	(357)
Net loss	(56,150)	0	0	(56,150)	0	0
Unrealized gain on investments	161	0	0	0	161	0
Other	61	$ 0	61	0	0	0
Balance, shares at Jun. 30, 2015		103,851
Balance, value at Jun. 30, 2015	231,474	$ 104	1,394,421	(1,160,402)	98	(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	3,792	$ 0	3,792	0	0	0
Issuance of common stock under Equity Incentive Plans, shares		292
Issuance of common stock under Equity Incentive Plans, value	752	$ 0	752	0	0	0
Repurchase of common stock	(621)	0	0	0	0	(621)
Net loss	(72,995)	0	0	(72,995)	0	0
Unrealized gain on investments	555	$ 0	0	0	555	0
Balance, shares at Jun. 30, 2016		104,152
Balance, value at Jun. 30, 2016	$ 217,333	$ 104	$ 1,402,190	$ (1,181,929)	$ 336	$ (3,368)