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Commitments and Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Commitments and Contingencies [Line Items]      
Rental expense $ 57.0 $ 57.0 $ 49.6
Rental income form subleases in 2013 0.4    
Rental income form subleases in 2014 0.2    
Rental income from subleases in 2015 0.2    
Rental income from subleases in 2016 0.1    
Rental income from subleases in 2017 $ 0.1