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Accrued Expenses - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Schedule of Accrued Liabilities [Line Items]        
Deferred revenue recognized $ 1.8 $ 1.8 $ 3.6 $ 4.7