Loss Per Share - Computation of Basic and Diluted 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 (both basic and diluted):
Net loss	$ (38,877)	$ (27,777)	$ (27,476)	$ (27,336)	$ (40,054)	$ (30,531)	$ (94,130)	$ (97,921)
Denominator:
Denominator for basic and diluted loss per share (in shares)	25,606,264			26,509,944			26,551,592	26,430,681
Basic loss per common share (in dollars per share)	$ (1.52)			$ (1.03)			$ (3.55)	$ (3.70)
Diluted loss per common share (in dollars per share)	$ (1.52)			$ (1.03)			$ (3.55)	$ (3.70)