Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock	Preferred Stock	Preferred Stock Series A Convertible Preferred Stock	Common Stock	Additional paid-in capital	Additional paid-in capital Series A Convertible Preferred Stock	Accumulated deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect from adoption of new accounting standard	$ 0					$ 100		$ (100)
Balance at Dec. 31, 2015	14,203		$ 0		$ 15	161,359		(147,171)
Balance, preferred stock (shares) at Dec. 31, 2015			0
Balance, common stock (shares) at Dec. 31, 2015					14,634,855
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	1,933					1,933
Issuance of shares under “At-The-Market” equity program, net of offering costs (in shares)					53,280
Issuance of Series A convertible preferred stock with detachable warrants, net of issuance costs of $377 (shares)					53,280
Intrinsic value of beneficial ownership conversion feature, net of issuance costs	7,017					7,017
Issuance of common stock with detachable warrants net of issuance costs $1,175 (shares)					53,280
Net loss	(15,292)							(15,292)
Balance at Dec. 31, 2016	$ 7,861		$ 0		$ 15	170,409		(162,563)
Balance, preferred stock (shares) at Dec. 31, 2016		0	0
Balance, common stock (shares) at Dec. 31, 2016	14,688,135				14,688,135
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	$ 322					322
Issuance of shares under “At-The-Market” equity program, net of offering costs (in shares)				8,000	11,220,260
Issuance of Series A convertible preferred stock with detachable warrants net of issuance costs of $377	9,305	$ 7,623			$ 11	9,294	$ 7,623
Issuance of Series A convertible preferred stock with detachable warrants, net of issuance costs of $377 (shares)				8,000	11,220,260
Exercise of liability-classified warrants	41					41
Exercise of liability-classified warrants (shares)					6,941
Conversion of promissory notes	95					95
Conversion of promissory notes (shares)					24,911
Issuance of common stock with detachable warrants net of issuance costs $1,175	9,305	$ 7,623			$ 11	9,294	$ 7,623
Issuance of common stock with detachable warrants net of issuance costs $1,175 (shares)				8,000	11,220,260
Net loss	(16,240)							(16,240)
Balance at Dec. 31, 2017	$ 9,007		$ 0		$ 26	$ 187,784		$ (178,803)
Balance, preferred stock (shares) at Dec. 31, 2017		8,000	8,000
Balance, common stock (shares) at Dec. 31, 2017	25,940,247				25,940,247