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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Income Tax [Line Items]      
Income tax expense benefit $ 0.2 $ 0.7  
Effective tax rate 22.20% 18.40%  
Unrecognized tax benefits 4.2   4.0
Unrecognized tax benefits that, if recognized, would reduce the annual effective tax rate 4.1   3.9
Unrecognized tax benefits that, interests 0.2    
Unrecognized tax benefits that, penalties 0.1    
Unrecognized tax benefits expected decrease $ 1.6