Statements of Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock [Member]	Series A-1 Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] Series A Convertible Preferred Stock [Member]	Common Stock [Member] Series A-1 Convertible Preferred Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2013	$ 4,942		$ 2,054	$ 1			$ 40,969	$ (38,082)
Series A convertible preferred stock, Beginning balance at Dec. 31, 2013		$ 7,920
Beginning balance, shares at Dec. 31, 2013			2,054	11,788,045
Series A convertible preferred stock, Beginning balance, shares at Dec. 31, 2013		7,920
Issuance of common stock under Lincoln Park Capital, LLC purchase agreement	1,886						1,886
Issuance of common stock under Lincoln Park Capital, LLC purchase agreement, shares				700,000
Issuance of common stock under employee stock purchase plan	61						61
Issuance of common stock under employee stock purchase plan, shares				32,515
Stock-based compensation expense	1,846						1,846
Dividends issued on Series A and Series A-1 convertible preferred stock	3,774	$ 356	$ 240				3,534
Dividends issued on Series A and Series A-1 convertible preferred stock, shares		356	240
Fair value of Series A and Series A-1 convertible preferred stock dividends	(4,130)						(4,130)
Exchange of Series A convertible preferred stock into Series A-1 convertible preferred stock	3,000	$ (3,000)	$ 3,000
Exchange of Series A convertible preferred stock into Series A-1 convertible preferred stock, shares		(3,000)	3,000
Conversions of Series A and Series A-1 convertible preferred stock into common stock	166	$ (166)	$ (3,716)	$ 1			3,881
Conversions of Series A and Series A-1 convertible preferred stock into common stock, shares		(166)	(3,716)	9,463,712	405,720	9,057,992
Net loss	(8,800)							(8,800)
Ending balance at Dec. 31, 2014	2,745		$ 1,578	$ 2			48,047	(46,882)
Series A convertible preferred stock, Ending balance at Dec. 31, 2014		$ 5,110
Ending balance, shares at Dec. 31, 2014			1,578	21,984,272
Series A convertible preferred stock, Ending balance, shares at Dec. 31, 2014		5,110
Issuance of common stock under Lincoln Park Capital, LLC purchase agreement	64						64
Issuance of common stock under Lincoln Park Capital, LLC purchase agreement, shares				50,000
Issuance of common stock in exchange for patent and technology rights	228						228
Issuance of common stock in exchange for patent and technology rights, shares				200,000
Issuance of common stock in connection with public offering, net of offering costs of $1,198	9,202			$ 3			9,199
Issuance of common stock in connection with public offering, net of offering costs of $1,198, shares				26,000,000
Issuance of common stock under employee stock purchase plan	31						31
Issuance of common stock under employee stock purchase plan, shares				69,546
Issuance of common stock upon exercise of warrants in connection with public offering	198						198
Issuance of common stock upon exercise of warrants in connection with public offering, shares				435,000
Stock-based compensation expense	1,535						1,535
Dividends issued on Series A and Series A-1 convertible preferred stock	104	$ 105	$ 21				83
Dividends issued on Series A and Series A-1 convertible preferred stock, shares		105	21
Fair value of Series A and Series A-1 convertible preferred stock dividends	209						209
Exchange of Series A convertible preferred stock into Series A-1 convertible preferred stock	2,000	$ (2,000)	$ 2,000
Exchange of Series A convertible preferred stock into Series A-1 convertible preferred stock, shares		(2,000)	2,000
Conversions of Series A and Series A-1 convertible preferred stock into common stock	$ 3,215	$ (3,215)	$ (3,599)	$ 2			6,812
Conversions of Series A and Series A-1 convertible preferred stock into common stock, shares	435,000	(3,215)	(3,599)	16,610,303	7,837,400	8,772,903
Net loss	$ (10,223)							(10,223)
Ending balance at Dec. 31, 2015	$ 8,890			$ 7			$ 65,988	$ (57,105)
Ending balance, shares at Dec. 31, 2015				65,349,121
Series A convertible preferred stock, Ending balance, shares at Dec. 31, 2015		0