Summary of Significant Accounting Policies - Computation of Earnings (Loss) per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Basic earnings (loss) per share computation:
Net loss attributable to common stockholders —basic and diluted	$ (5,298)	$ (7,113)	$ (3,989)	$ (8,724)	$ (14,390)	$ (3,945)	$ (13,119)	$ (4,802)	$ (25,124)	$ (36,256)
Weighted average common shares - basic and diluted (in shares)									53,839,139	53,592,930
Basic and diluted loss per share (in dollars per share)									$ (0.47)	$ (0.68)