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Derivative Financial Instruments - Additional Information (Detail) (Interest Rate Swap, Cash Flow Hedging, Designated as Hedging Instrument, USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Investment
Derivative Instruments and Hedging Activities Disclosure [Line Items]  
Number of interest swap agreements 7us-gaap_DerivativeNumberOfInstrumentsHeld
Notional amount of derivatives $ 210.0invest_DerivativeNotionalAmount
Minimum
  
Derivative Instruments and Hedging Activities Disclosure [Line Items]  
Derivative interest rate, one-month LIBOR interest rate 1.20%us-gaap_DerivativeFixedInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum
  
Derivative Instruments and Hedging Activities Disclosure [Line Items]  
Derivative interest rate, one-month LIBOR interest rate 2.20%us-gaap_DerivativeFixedInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember