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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Income Taxes [Line Items]          
Effective tax rate 39.00% 43.00% 38.00% 42.00%  
Federal tax credits $ 0.1   $ 0.2   $ 0.4