Stockholders' Equity (Details) - USD ($) $ in Thousands	1 Months Ended			6 Months Ended
	Jul. 31, 2018	Nov. 30, 2017	May 31, 2016	Jun. 30, 2018	Jun. 30, 2017
Common Stock
Aggregate offering price stock sale			$ 60,000
Additional offering price stock sale authorized		$ 75,000
Net proceeds from sale of common stock				$ 19,960	$ 21,489
Subsequent Event
Common Stock
Common stock issued (in shares)	5,685,350
Net proceeds from sale of common stock	$ 2,800
Common Stock
Common Stock
Shares Issued in Connection with Cantor Agreement (in shares)				17,953,046
Aggregate gross offering price available				$ 47,000