Schedule of Components of Income Tax (Detail) - USD ($) $ 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
Schedule Of Income Taxes [Line Items]
Current, Federal									$ 20,777	$ 65,636	$ 14,521
Current, State				$ 900					4,066	3,192	2,639
Current, City									678	533	439
Current, Foreign									40,011	256,117	61,393
Total current provision									65,532	325,478	78,992
Deferred, Federal									(915)	(150)	(537)
Deferred, State									(170)	(28)	(99)
Deferred, City									(28)	(5)	(16)
Deferred, Foreign									(5,202)	5,480	(3,665)
Total deferred expense (benefit)									(6,315)	5,297	(4,317)
Total provision for income taxes	$ 25,384	$ 9,607	$ 13,355	$ 10,871	$ 14,372	$ 286,513	$ 18,804	$ 11,086	$ 59,217	$ 330,775	$ 74,675