Income Taxes - Difference Between Total Tax Expense and Amount Computed by Applying Statutory Federal Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Statutory rate applied to income	$ 353,259	$ 376,019	$ 393,288
Plus state income taxes, net of Federal tax benefit	27,918	29,211	32,295
Earnings in jurisdictions taxed at rates different from the U.S. statutory rate	(33,984)	(18,057)	(13,684)
U.S. tax reform - transition tax	37,132	0	0
Other	3,670	(73)	6,110
Income tax expense, total	392,511	387,100	418,009
Domestic Tax Authority [Member]
Income Tax Contingency [Line Items]
Deferred tax remeasurement	13,854	0	0
Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Deferred tax remeasurement	$ (9,338)	$ 0	$ 0