Net Loss Per Common Share - Earning Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Comprehensive loss	$ (6,079)	$ (6,678)	$ (7,224)	$ (8,671)	$ (10,502)	$ (7,496)	$ (19,981)	$ (26,669)
Denominator:
Basic and diluted weighted average common shares outstanding	14,259,691			10,623,601			13,650,556	10,253,437
Basic and diluted	$ (0.43)			$ (0.82)			$ (1.46)	$ (2.60)