Net Loss Per Share - Computation of Basic and Diluted Net (Loss) Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net loss	$ (10,429)	$ 1,998	$ (903)	$ 730	$ (3,545)	$ (333)	$ (19,899)	$ (5,505)	$ (8,604)	$ (29,282)	$ (1,930)
Weighted average common basic shares									41,286	41,085	41,030
Basic and diluted net loss per share	$ (0.26)	$ 0.05	$ (0.02)	$ 0.02	$ (0.09)	$ (0.01)	$ (0.48)	$ (0.13)	$ (0.21)	$ (0.71)	$ (0.05)