Net Loss Per Share - Computation of Net (Loss) Income Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net loss	$ (17,442)	$ (17,455)	$ (24,295)	$ (9,321)	$ (4,153)	$ (18,724)	$ (2,346)	$ (25,562)	$ (68,512)	$ (50,785)	$ (45,719)
Weighted average shares-basic (shares)									72,824,070	64,882,417	64,708,163
Net (loss) income per share-basic ($ per share)	$ (0.22)	$ (0.22)	$ (0.35)	$ (0.14)	$ (0.07)	$ (0.28)	$ (0.04)	$ (0.39)	$ (0.94)	$ (0.78)	$ (0.71)
Weighted average shares-diluted (shares)									72,824,070	64,882,417	64,708,163
Net (loss) income per share-diluted ($ per share)									$ (0.94)	$ (0.78)	$ (0.71)