Derivative Instruments and Hedging Activities - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, liability	$ 25,000
Aggregate fair value of net liability position	9,900
Collateral posted with counterparties	40,500
Interest Rate Swaps
Derivative [Line Items]
Accumulated net after-tax losses related to effective cash flow hedges	16,700		$ 14,500
Estimated amount of interest rate derivatives to be reclassified to interest expense	$ 9,900
Recognized a net reduction to interest expense		$ 100