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Debt and Financing Arrangements - Summary of Unsecured Credit Facility (Detail)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Debt Disclosure [Abstract]    
Weighted average rates 2.21%us-gaap_DebtWeightedAverageInterestRate 2.69%us-gaap_DebtWeightedAverageInterestRate
Range of effective rates, minimum 1.88%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMinimum 1.87%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMinimum
Range of effective rates, maximum 3.25%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMaximum 3.41%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMaximum