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	May 2018 Registered Direct Offering	May 2018 Registered Direct Offering Common Stock	May 2018 Registered Direct Offering Additional paid-in capital	July 2018 Registered Direct Offering	July 2018 Registered Direct Offering Common Stock	July 2018 Registered Direct Offering Additional paid-in capital	December 2018 Private Placement	December 2018 Private Placement Common Stock	December 2018 Private Placement Additional paid-in capital
Balance, preferred stock (shares) at Dec. 31, 2016			0
Balance at Dec. 31, 2016	$ 7,861		$ 0		$ 15	$ 170,409		$ (162,563)
Balance, common stock (shares) at Dec. 31, 2016					2,939,329
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of the March 2017 and May 2018 reverse stock splits on common stock and additional paid in capital, beginning balance					$ (12)	12
Issuance of stock (shares)				8,000	2,244,053
Issuance of stock	9,305	$ 7,623			$ 2	9,303	$ 7,623
Stock-based compensation expense	322					322
Exercise of liability-classified warrants (shares)					1,389
Exercise of liability-classified warrants	41					41
Conversion of promissory notes (shares)					4,984
Conversion of promissory notes	95					95
Net loss	$ (16,240)							(16,240)
Balance, preferred stock (shares) at Dec. 31, 2017	8,000		8,000
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock (shares)										2,038,224			1,474,080			443,350
Issuance of stock									$ 5,324	$ 2	$ 5,322	$ 3,591	$ 1	$ 3,590	$ 863	$ 1	$ 862
Stock-based compensation expense	$ 526					526
Exercise of liability-classified warrants (shares)					129,702
Exercise of liability-classified warrants	499					499
Net loss	(10,277)							(10,277)
Conversion of pre-funded units (shares)					483,221
Conversion of pre-funded units	$ 24				$ 1	23
Balance, preferred stock (shares) at Dec. 31, 2018	8,000		8,000
Balance at Dec. 31, 2018	$ 9,557		$ 0		$ 10	$ 198,627		$ (189,080)
Balance, common stock (shares) at Dec. 31, 2018	9,758,332				9,758,332