CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance (in shares) at Dec. 31, 2012		56,252
Balance at Dec. 31, 2012	$ 19,107	$ 56	$ 478,903		$ (459,852)
Net loss	(43,337)				(43,337)
Other comprehensive income	7			$ 7
Issuance of common stock from public offering, net of offering costs (in shares)		15,019
Issuance of common stock from public offering, net of offering costs	61,454	$ 15	61,439
Issuance of common stock from exercise of stock options and/or warrants, and purchases from ESPP(In Shares)		588
Issuance of common stock from exercise of stock options and warrants, and purchases from ESPP	2,296	$ 1	2,295
Stock-based compensation	3,268		3,268
Balance (in shares) at Dec. 31, 2013		71,859
Balance at Dec. 31, 2013	42,795	$ 72	545,905	7	(503,189)
Net loss	(38,755)				(38,755)
Other comprehensive income	(38)			(38)
Issuance of common stock from public offering, net of offering costs (in shares)		4,341
Issuance of common stock from public offering, net of offering costs	18,521	$ 4	18,517
Issuance of common stock from exercise of stock options and/or warrants, and purchases from ESPP(In Shares)		4,204
Issuance of common stock from exercise of stock options and warrants, and purchases from ESPP	13,845	$ 4	13,841
Stock-based compensation	5,153		5,153
Balance (in shares) at Dec. 31, 2014		80,404
Balance at Dec. 31, 2014	41,521	$ 80	583,416	(31)	(541,944)
Net loss	(55,868)				(55,868)
Other comprehensive income	7,320			7,320
Issuance of common stock from public offering, net of offering costs (in shares)		14,636
Issuance of common stock from public offering, net of offering costs	75,376	$ 15	75,361
Issuance of common stock from exercise of stock options and/or warrants, and purchases from ESPP(In Shares)		4,055
Issuance of common stock from exercise of stock options and warrants, and purchases from ESPP	19,686	$ 4	19,682
Stock-based compensation	6,730		6,730
Balance (in shares) at Dec. 31, 2015		99,095
Balance at Dec. 31, 2015	$ 94,765	$ 99	$ 685,189	$ 7,289	$ (597,812)