Property and Equipment - Depreciation and Amortization Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 24,574	$ 22,707	$ 21,239
Depreciation & amortization
Property, Plant and Equipment [Line Items]
Effect of the foreign exchange gains (losses) upon settlement of cash flow hedges	$ 435