Income Taxes - Reconciliation of Income Tax Expense Computed by Applying the United States Federal Income Tax Rate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Provision of Income Taxes [Line Items]
Federal statutory income tax rate	35.00%	35.00%	35.00%
Computed “expected” tax expense	$ 213,811	$ 200,408	$ 192,638
Increase in income taxes resulting from:
State income taxes, net of Federal income tax benefit	10,751	10,758	8,111
Nondeductible stock compensation expense, net	8,069	9,927	12,061
Other, net	(1,202)	1,492	4,614
Income tax expense	$ 231,429	$ 222,585	$ 217,424