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Intangible Assets - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Schedule of Actual and Estimated Amortization Expense [Line Items]        
Increase in finite lived intangible assets     $ 24.3  
Amortization expense for intangible assets 0.8 0.8 1.9 2.4
Estimated amortization expense for the remainder of 2012 1.4   1.4  
Estimated amortization expense for 2013 5.2   5.2  
Estimated amortization expense for 2014 4.6   4.6  
Estimated amortization expense for 2015 4.6   4.6  
Estimated amortization expense for 2016 4.6   4.6  
Estimated amortization expense for 2017 $ 4.6   $ 4.6