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Retirement Plans - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]      
Expense of retirement plans related to the 401(k) Plans $ 34.3us-gaap_DefinedContributionPlanCostRecognized $ 29.8us-gaap_DefinedContributionPlanCostRecognized $ 24.8us-gaap_DefinedContributionPlanCostRecognized