Cash Flow Hedges, Gains (Losses) Recorded as Component of Other Comprehensive Income (Loss) or Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Opening balance, before-tax amount	$ (30,090)	$ (66,786)	$ (205,952)
Net gains (losses) reclassified into statement of income upon completion of hedged transactions, before-tax amount	(6,799)	(42,106)	(49,161)
Changes in fair value of effective portion of outstanding derivatives, net, before-tax amount	60,752	(5,410)	90,005
Gain (loss) on cash flow hedging derivatives, net, before-tax amount	67,551	36,696	139,166
Closing balance, before-tax amount	37,461	(30,090)	(66,786)
Opening balance, tax (expense) or benefit	9,830	23,646	72,612
Net gains (losses) reclassified into statement of income upon completion of hedged transactions, tax (expense) or benefit	409	15,346	17,498
Changes in fair value of effective portion of outstanding derivatives, net, tax (expense) or benefit	(23,400)	1,530	(31,468)
Gain (loss) on cash flow hedging derivatives, net, tax (expense) or benefit	(23,809)	(13,816)	(48,966)
Closing balance, tax (expense) or benefit	(13,979)	9,830	23,646
Opening balance, net of tax amount	(20,260)	(43,140)	(133,340)
Net gains (losses) reclassified into statement of income upon completion of hedged transactions, net of tax amount	(6,390)	(26,760)	(31,663)
Changes in fair value of effective portion of outstanding derivatives, net, net of tax amount	37,352	(3,880)	58,537
Gain (loss) on cash flow hedging derivatives, net of taxes amount	43,742	22,880	90,200
Closing balance, net of tax amount	$ 23,482	$ (20,260)	$ (43,140)