Subsequent Events Subsequent Events (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Jan. 31, 2018	May 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Proceeds from sale of common stock, net			$ 56,486	$ 26,223	$ 12,518
Credit facility, maximum borrowing capacity			$ 15,000
At the market equity offering
Subsequent Event [Line Items]
Proceeds from sale of common stock, net	$ 40,000	$ 40,000