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Earnings Per Share - Additional Information (Detail) (Stock Option [Member])
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Stock Option [Member]
 
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]  
Anti-dilutive shares not included in the computation of basic and diluted income per share 0.1us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_StockOptionMember