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Accrued Expenses - 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 Accrued Liabilities [Line Items]        
Deferred revenue recognized $ 1.8 $ 1.8 $ 5.4 $ 6.6