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Difference Between Statutory Federal Income Tax Rate And Effective Income Rate (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Reconciliation of Statutory Federal Tax Rate [Line Items]      
Statutory tax rate 35.00% 35.00% 35.00%
State income taxes 2.50% 2.50% 1.10%
Permanent differences (0.20%) (0.10%) 2.30%
Other, net (0.30%) (0.60%) (0.20%)
Effective tax rate 37.00% 36.80% 38.20%