Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator [Abstract]
Net loss	$ (18,412)	$ (20,472)	$ (14,726)	$ (15,038)	$ (36,493)	$ 4,099	$ (53,610)	$ (47,432)
Denominator [Abstract]
Weighted-average number of common shares - basic (in shares)	25,031,478			23,646,192			24,992,229	19,335,541
Loss per common share - basic (in dollars per share)	$ (0.74)			$ (0.64)			$ (2.15)	$ (2.45)
Stock Options [Member]
Dilutive Instruments [Abstract]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)							2,256,092
Unvested Restricted Stock Units [Member]
Dilutive Instruments [Abstract]
Anti-dilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)							107,144