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Cash flow hedges and non-hedging derivatives outstanding (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Derivative Asset Fair Value Net [Abstract]    
Derivative Asset, Fair Value, Gross Asset $ 22,485us-gaap_DerivativeFairValueOfDerivativeAsset $ 25,362us-gaap_DerivativeFairValueOfDerivativeAsset
Derivative Liability Fair Value Net [Abstract]    
Derivative Fair Value Of Derivative Liability 21,376us-gaap_DerivativeFairValueOfDerivativeLiability 23,032us-gaap_DerivativeFairValueOfDerivativeLiability
Fair Value, Measurements, Recurring [Member]    
Derivative Asset Fair Value Net [Abstract]    
Derivative Asset, Fair Value, Gross Asset $ 22,485us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 $ 25,362us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember