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, 2015	Dec. 31, 2014	Dec. 31, 2013
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal statutory income tax rate	35.00%	35.00%	35.00%
Computed “expected” tax expense	$ 257,841	$ 213,811	$ 200,408
Increase in income taxes resulting from:
State income taxes, net of Federal income tax benefit	11,272	10,751	10,758
Nondeductible stock compensation expense, net	5,241	8,069	9,927
Other, net	2,838	(1,202)	1,492
Income tax expense	$ 277,192	$ 231,429	$ 222,585