Summary of Significant Accounting Policies - Computation of Earnings (Loss) per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic loss per share computation:
Net loss	$ (3,989)	$ (13,119)	$ (12,713)	$ (17,921)
Weighted average common shares - basic and diluted (in shares)	53,849,108	53,510,712	53,827,665	53,484,756
Basic and diluted loss per share (in dollars per share)	$ (0.08)	$ (0.25)	$ (0.24)	$ (0.34)