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Income Taxes (Schedule of Components of the Provision for Income Taxes) (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Income Taxes      
Federal income taxes at statutory rate $ 285,524 $ 241,281 $ 173,914
State income taxes, net of federal tax benefit 16,132 22,267 18,896
Other items, net 6,444 6,452 (3,410)
Provision for income taxes $ 308,100 $ 270,000 $ 189,400