Stockholders' Equity (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended
	Apr. 30, 2019	Nov. 30, 2017	May 31, 2016	Mar. 31, 2019	Mar. 31, 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				$ 4,151	$ 11,689
Common Stock
Common Stock
Shares Issued in Connection with Cantor Agreement (in shares)				883,569	312,802
Aggregate gross offering price available				$ 33,300
Net proceeds from sale of common stock				$ 4,200
Common Stock | Subsequent Event
Common Stock
Common stock issued (in shares)	924,167
Net proceeds from sale of common stock	$ 4,100