Subsequent Event (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Mar. 04, 2019	Mar. 31, 2019	Dec. 31, 2017	Dec. 31, 2016
Subsequent Events
Proceeds from the issuance of common stock, net			$ 18,535	$ 37,528
Common Stock
Subsequent Events
Shares issued (in shares)			5,333,334	6,338,583
Subsequent Event | Private Placement
Subsequent Events
Proceeds from the issuance of common stock, net	$ 7,800	$ 7,800
Subsequent Event | Private Placement | Common Stock
Subsequent Events
Shares issued (in shares)	8,400,000
Share price (in dollars per share)	$ 0.93