Income Taxes - Summary of Components of Income Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ 4,626	$ 12,652	$ 25,045
Foreign	80,408	71,232	50,731
Income before income tax expense	$ 85,034	$ 83,884	$ 75,776