Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance of unrecognized tax benefits at beginning of year	$ 24,278	$ 21,079	$ 14,780
Increases for tax positions of prior years	2,478	58	1,449
Decreases for tax positions of prior years	(114)	(361)	(47)
Increases for tax positions established for the current period	1,677	5,185	9,866
Decreases for settlements with taxing authorities	(154)	(167)	(594)
Reductions resulting from lapse of applicable statute of limitation	(1,155)	(1,310)	(4,218)
Adjustment resulting from foreign currency translation	227	(206)	(157)
Balance of unrecognized tax benefits at end of year	$ 27,237	$ 24,278	$ 21,079