Income Taxes - Summary of Net Loss Before Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
United States	$ (27,820)	$ (27,908)	$ (28,870)
International	1,937	(1,165)	(4,492)
Loss before provision (benefit) for income taxes	$ (25,883)	$ (29,073)	$ (33,362)