Net Income (Loss) Per Common Share - Reconciliation of the Numerators and Denominators of Basic and Diluted Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net loss used to compute net loss per common share:
Basic					$ (30,704)	$ (22,997)	$ (15,752)
Adjustment for change in fair value of liability classified stock options					(187)
Diluted					$ (30,891)	$ (22,997)	$ (15,752)
Weighted average number of common shares:
Basic					17,985,061	15,493,474	14,281,837
Adjustment for dilutive effect of stock options					16,698
Diluted					18,001,759	15,493,474	14,281,837
Net loss per common share - basic	$ (0.45)	$ (0.43)	$ (0.41)	$ (0.42)	$ (1.71)	$ (1.48)	$ (1.10)
Net loss per common share - diluted	$ (0.45)	$ (0.43)	$ (0.41)	$ (0.43)	$ (1.72)	$ (1.48)	$ (1.10)