Income Taxes - Reconciliation of Income Tax Expense Computed by Applying the United States Federal Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal statutory income tax rate	35.00%	35.00%	35.00%
Computed “expected” tax expense	$ 251,508	$ 240,400	$ 257,841
Increase in income taxes resulting from:
State income taxes, net of Federal income tax benefit	12,525	9,759	11,272
Nondeductible stock compensation expense, net	63	3,629	5,241
Enactment of 2017 Tax Act	(13,894)
Effect of lower foreign tax rates	(25,374)
Other, net	3,384	535	2,838
Income tax expense	$ 228,212	$ 254,323	$ 277,192