Business and Organization (Details) - USD ($) $ / shares in Units, $ in Thousands						3 Months Ended		6 Months Ended
	Jul. 05, 2018	Jul. 02, 2018	May 31, 2018	Jan. 06, 2018	Dec. 11, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	May 24, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Sale of common stock (shares)				409,091
Common stock, par value (in dollars per share)						$ 0.001		$ 0.001		$ 0.001	$ 0.001
Purchase price (in usd per share)				$ 3.80
Number of warrants (shares)						6,436,304		6,436,304			5,452,923
Warrant exercise price (in dollars per share)						$ 9.83		$ 9.83			$ 11.32
Proceeds from common stock offering, net			$ 5,400		$ 9,300			$ 5,473	$ 0
Net loss						$ 2,894	$ 14,018	5,795	19,025
Cash used in operating activities								7,476	8,983
Cash and cash equivalents						15,410	$ 15,912	15,410	$ 15,912		$ 17,417	$ 17,515
Working capital						13,800		13,800
Accumulated deficit						184,598		184,598			178,803
Stockholders equity						$ 9,368		$ 9,368			$ 9,007
Warrant
Class of Stock [Line Items]
Number of warrants (shares)						5,125,788		5,125,788			4,067,367
Subsequent Event | July 2018 Purchase Agreement
Class of Stock [Line Items]
Sale of common stock (shares)		1,474,080
Common stock, par value (in dollars per share)		$ 0.001
Purchase price (in usd per share)		$ 2.69
Percentage of shares of common stock sold		65.00%
Proceeds from common stock offering, net	$ 3,500
Subsequent Event | Warrants Issued in July 2018 Private Placement | Warrant
Class of Stock [Line Items]
Purchase price (in usd per share)		$ 0.125
Number of warrants (shares)		958,152
Warrant exercise price (in dollars per share)	$ 3.464	$ 2.70
Warrant exercise period	5 years	5 years 6 months
Shares of common stock available for purchase (in shares)	103,186