Loss per Common Share - Computation of Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Loss per Common Share
Net loss	$ (13,060)	$ (21,121)	$ (31,712)	$ (44,199)
Loss attributable to common shareholders — basic and diluted	$ (13,060)	$ (21,121)	$ (31,712)	$ (44,199)
Weighted-average number of common shares used in net loss per share - basic and diluted	32,967,718	29,441,514	32,935,873	29,396,143
Loss per share - basic and diluted	$ (0.40)	$ (0.72)	$ (0.96)	$ (1.50)