Condensed Consolidated Statements of Stockholders' Equity (Deficit) (unaudited) - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock	Preferred Stock Series A Convertible Preferred Stock	Common Stock	Additional paid-in capital	Accumulated deficit
Beginning balance at Dec. 31, 2017	$ 9,007		$ 0	$ 5	$ 187,805	$ (178,803)
Balance, common stock (shares) at Dec. 31, 2017	5,189,755			5,189,755
Balance, preferred stock (shares) at Dec. 31, 2017		8,000	8,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of pre-funded warrants	$ 24			$ 1	23
Conversion of pre-funded warrants (shares)				483,221
Stock-based compensation expense	260				260
May 2018 Registered Direct Offering, net of offering costs of $627	5,373			$ 2	5,371
May 2018 Direct Registered Offering (in shares)				2,038,224
Exercise of warrants	499				499
Exercise of warrants (in shares)				129,702
Net loss	(5,795)					(5,795)
Ending balance at Jun. 30, 2018	$ 9,368		$ 0	$ 8	$ 193,958	$ (184,598)
Balance, common stock (shares) at Jun. 30, 2018	7,840,902			7,840,902
Balance, preferred stock (shares) at Jun. 30, 2018		8,000	8,000