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Allowance for Doubtful Accounts Included in Accounts Receivable, Net (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Sep. 30, 2011
Valuation Allowance [Line Items]      
Allowance for Doubtful Accounts $ 2.7 $ 2.3 $ 2.5