Stockholders' Equity (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended				6 Months Ended
	Jul. 31, 2019	Nov. 30, 2017	May 31, 2016	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Common Stock
Aggregate offering price stock sale			$ 60,000
Additional offering price stock sale authorized		$ 75,000
Net proceeds from sale of common stock								$ 11,363	$ 19,960
Common Stock
Common Stock
Shares Issued in Connection with Cantor Agreement (in shares)				1,972,428	883,569	884,068	312,802	2,856,194
Aggregate gross offering price available				$ 25,800				$ 25,800
Net proceeds from sale of common stock								$ 11,400
Common Stock | Subsequent Event
Common Stock
Common stock issued (in shares)	201,687
Net proceeds from sale of common stock	$ 500