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Reconciliation of Effective Income Tax Rate (Detail)
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Reconciliation of Effective Income Tax Rate [Line Items]        
Statutory income tax rate 25.00% 25.00% 25.00% 25.00%
US federal net operating loss 1.00% 0.00% 2.00% 3.00%
Effective tax rate 26.00% 25.00% 27.00% 28.00%