Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, liability	$ 25,000,000
Aggregate fair value of net liability position	13,300,000
Collateral posted with counterparties	40,700,000
Interest Rate Swaps [Member]
Derivative [Line Items]
Accumulated net after-tax losses related to effective cash flow hedges	18,800,000		14,500,000
Estimated amount of interest rate derivatives to be reclassified to interest expense	8,400,000
Recognized a net reduction to interest expense		$ 100,000