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Reconciliation of Federal Statutory Income Tax Rate to Effective Income Tax Rate (Parenthetical) (Detail)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Reconciliation of Statutory Federal Tax Rate [Line Items]      
Expected provision at federal statutory tax rate, percentage 35.00% 35.00% 35.00%