Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
BALANCE at Dec. 31, 2011	$ 31,017	$ 2	$ 340,979		$ (309,964)
BALANCE (in shares) at Dec. 31, 2011		22,624,000
Exercise of options for common stock	3,780		3,780
Exercise of options for common stock, shares	371,353	372,000
Exercise of warrants for common stock	52,742		52,742
Exercise of warrants for common stock, shares		1,770,000
Issuance of common stock for cash, net of offering costs	154,349	1	154,348
Issuance of common stock for cash, net of offering costs, shares		6,934,000
Stock-based compensation	3,078		3,078
Stock-based compensation, shares		4,000
Net loss	(121,287)				(121,287)
BALANCE at Dec. 31, 2012	123,679	3	554,927		(431,251)
BALANCE (in shares) at Dec. 31, 2012		31,704,000
Exercise of options for common stock	2,725		2,725
Exercise of options for common stock, shares	241,056	241,000
Exercise of warrants for common stock	96,768		96,768
Exercise of warrants for common stock, shares		2,336,000
Vest of restricted stock units	0	0	0	0	0
Vest of restricted stock units, shares		31,000
Shares withheld for taxes	(226)		(226)
Shares withheld for taxes, shares		(7,000)
Grant of restricted stock awards	0	0	0	0	0
Grant of restricted stock awards, shares		6,000
Issuance of common stock for cash, net of offering costs	125,104	1	125,103
Issuance of common stock for cash, net of offering costs, shares		3,441,000
Stock-based compensation	11,127		11,127
Net loss	(111,985)				(111,985)
BALANCE at Dec. 31, 2013	247,192	4	790,424		(543,236)
BALANCE (in shares) at Dec. 31, 2013		37,752,000
Exercise of options for common stock	980		980
Exercise of options for common stock, shares	86,007	86,000
Exercise of warrants for common stock	19,536		19,536
Exercise of warrants for common stock, shares		766,000
Vest of restricted stock units	0	0	0	0	0
Vest of restricted stock units, shares		7,000
Shares withheld for taxes	(34)		(34)
Shares withheld for taxes, shares		(1,000)
Grant of restricted stock awards	0	0	0	0	0
Grant of restricted stock awards, shares		6,000
Issuance of common stock for cash, net of offering costs	94,503		94,503
Issuance of common stock for cash, net of offering costs, shares		2,650,000
Issuance of common stock under employee stock purchase plan	1,015		1,015
Issuance of common stock under employee stock purchase plan, shares		46,000
Stock-based compensation	20,345		20,345
Unrealized loss from available-for-sale securities	(95)			(95)
Net loss	(135,789)				(135,789)
BALANCE at Dec. 31, 2014	$ 247,653	$ 4	$ 926,769	$ (95)	$ (679,025)
BALANCE (in shares) at Dec. 31, 2014		41,312,000