CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balances at Dec. 31, 2010	$ 132,002	$ 82	$ 432,041	$ 4	$ (300,125)
Balances (in shares) at Dec. 31, 2010		81,568,000
Increase (Decrease) in Stockholders' Equity
Sale of common stock through employee stock purchase plan	211		211
Sale of common stock through employee stock purchase plan (in shares)		36,000
Exercise of common stock options for cash	2,354		2,354
Exercise of common stock options for cash (in shares)		482,000
Share-based compensation expense	7,353		7,353
Proceeds from registered direct public offering of common stock	45,812	7	45,805
Proceeds from registered direct public offering of common stock (in shares)		6,889,000
Offering cost allocated to equity	(529)		(529)
Net unrealized gain on securities	21			21
Net loss	(46,140)				(46,140)
Balances at Dec. 31, 2011	141,084	89	487,235	25	(346,265)
Balances (in shares) at Dec. 31, 2011		88,975,000
Increase (Decrease) in Stockholders' Equity
Sale of common stock through employee stock purchase plan	314		314
Sale of common stock through employee stock purchase plan (in shares)		35,000
Exercise of common stock options for cash	13,251	3	13,248
Exercise of common stock options for cash (in shares)		2,649,000
Share-based compensation expense	16,133		16,133
Proceeds from registered direct public offering of common stock	202,500	9	202,491
Proceeds from registered direct public offering of common stock (in shares)		9,000,000
Offering cost allocated to equity	(10,500)		(10,500)
Net unrealized gain on securities	8			8
Net loss	(139,881)				(139,881)
Balances at Dec. 31, 2012	222,909	101	708,921	33	(486,146)
Balances (in shares) at Dec. 31, 2012	100,659,000	100,659,000
Increase (Decrease) in Stockholders' Equity
Sale of common stock through employee stock purchase plan	860		860
Sale of common stock through employee stock purchase plan (in shares)		103,000
Exercise of common stock options for cash	13,706	2	13,704
Exercise of common stock options for cash (in shares)		2,366,000
Vesting of restricted stock units (in shares)		33,000
Share-based compensation expense	32,877		32,877
Equity component of convertible debt	95,262		95,262
Offering cost allocated to equity	(3,113)		(3,113)
Purchase of capped call transaction	(34,709)		(34,709)
Net unrealized gain on securities	33			33
Net loss	(174,456)				(174,456)
Balances at Dec. 31, 2013	$ 153,369	$ 103	$ 813,802	$ 66	$ (660,602)
Balances (in shares) at Dec. 31, 2013	103,161,000	103,161,000