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, 2009	$ 186,726	$ 81	$ 420,708	$ (3)	$ (234,060)
Balances (in shares) at Dec. 31, 2009		80,607,000
Increase (Decrease) in Stockholders' Equity
Sale of common stock through employee stock purchase plan	304		304
Sale of common stock through employee stock purchase plan (in shares)		48,000
Exercise of common stock options for cash	3,617	1	3,616
Exercise of common stock options for cash (in shares)		913,000
Share-based compensation expense	7,413		7,413
Net unrealized gain on securities	7			7
Net loss	(66,065)				(66,065)
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
Issue costs for registered direct public offering of common stock	(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	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
Issue costs for registered direct public offering of common stock	(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