Summary of Significant Accounting Policies - Computation of Earnings (Loss) per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic loss per share computation:
Net loss	$ (7,113)	$ (3,945)	$ (19,826)	$ (21,866)
Weighted average common shares - basic and diluted (in shares)	53,850,427	53,625,768	53,835,336	53,532,277
Basic and diluted loss per share (in dollars per share)	$ (0.13)	$ (0.07)	$ (0.37)	$ (0.41)