Income Taxes - Income Tax Expense Reconciliation (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Expense Reconciliation
Income taxes computed at the federal statutory rate	$ 96,277	$ 72,652	$ 112,838
State income taxes, net of federal income tax benefit	3,226	7,974	7,731
Other, net	(5,014)	(2,470)	(4,181)
Total	$ 94,489	$ 78,156	$ 116,388