Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	May 31, 2016
Stockholders' Equity
Net proceeds from sale of common stock	$ 12,821
Cantor agreement
Stockholders' Equity
Common stock issued (in shares)	3,572,608
Net proceeds from sale of common stock	$ 12,800
Aggregate gross offering price available	$ 32,000
Cantor agreement | Maximum
Stockholders' Equity
Common stock available for sale (in shares)		60,000,000