STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock Series E Convertible Preferred Stock	Common Stock Series D Convertible Preferred Stock	Common Stock	Additional Paid-in Capital Series E Convertible Preferred Stock	Additional Paid-in Capital Series D Convertible Preferred Stock	Additional Paid-in Capital Series E Preferred Stock	Additional Paid-in Capital Series D Preferred Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss)/Income	Series E Convertible Preferred Stock	Series D Convertible Preferred Stock	Series E Preferred Stock	Series D Preferred Stock	Total
Beginning balance at Dec. 31, 2013			$ 66					$ 434,285	$ (412,884)	$ (7)	$ 5,528	$ 5,464			$ 32,452
Beginning balance, shares at Dec. 31, 2013			66,252								424	1,124
Sale of common stock and warrants, net of issuance costs			$ 8					37,229							37,237
Sale of common stock and warrants, shares			7,867
Exercise of common stock options, warrants and employee stock purchases			$ 6					8,450							8,456
Exercise of common stock options, warrants and employee stock purchases, shares			5,932
Issuance of common stock for services								82							82
Issuance of common stock for services, shares			27
Non-employee stock option expense								24							24
Stock-based compensation								4,322							4,322
Convertible preferred stock dividends						$ (453)	$ (66)						$ (453)	$ (66)
Unrealized gain (loss) on marketable securities										(10)					(10)
Conversion of preferred stock to common	$ 9	$ 6		$ 5,519	$ 5,458						$ (5,528)	$ (5,464)
Conversion of preferred stock to common, shares	(8,485)	(6,266)									(424)	(1,124)
Net loss									(38,642)						(38,642)
Ending balance at Dec. 31, 2014			$ 95					494,850	(451,526)	(17)					43,402
Ending balance, shares at Dec. 31, 2014			94,829
Sale of common stock and warrants, net of issuance costs			$ 23					80,576							80,599
Sale of common stock and warrants, shares			23,000
Exercise of common stock options, warrants and employee stock purchases			$ 3					2,543							2,546
Exercise of common stock options, warrants and employee stock purchases, shares			3,402
Issuance of common stock for services								122							122
Issuance of common stock for services, shares			34
Non-employee stock option expense								143							143
Stock-based compensation								5,442							5,442
Unrealized gain (loss) on marketable securities										(117)					(117)
Net loss									(48,555)						(48,555)
Ending balance at Dec. 31, 2015			$ 121					583,676	(500,081)	(134)					$ 83,582
Ending balance, shares at Dec. 31, 2015			121,265												121,265
Sale of common stock and warrants, net of issuance costs			$ 26					48,822							$ 48,848
Sale of common stock and warrants, shares			26,225
Exercise of common stock options, warrants and employee stock purchases			$ 2					2,342							2,344
Exercise of common stock options, warrants and employee stock purchases, shares			1,575
Stock-based compensation								6,847							6,847
Unrealized gain (loss) on marketable securities										117					117
Net loss									(38,389)						(38,389)
Ending balance at Dec. 31, 2016			$ 149					$ 641,687	$ (538,470)	$ (17)					$ 103,349
Ending balance, shares at Dec. 31, 2016			149,065												149,065