Derivative Financial Instruments - Impact of Derivatives on Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 38,746	$ 5,238
Derivative Liabilities	(40,855)	(28,688)
Interest rate swaps
Derivatives, Fair Value [Line Items]
Derivative Assets	38,746	5,238
Derivative Liabilities	(40,855)	(28,688)
Total net derivatives	(2,109)	(23,450)
Interest rate swaps | Trading
Derivatives, Fair Value [Line Items]
Derivative Assets	1,827	226
Derivative Liabilities	0	(1,370)
Total net derivatives	1,827	(1,144)
Interest rate swaps | Cash Flow | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Derivative Liabilities	(40,855)	(21,435)
Total net derivatives	(40,855)	(21,435)
Interest rate swaps | Fair Value | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Assets	36,919	5,012
Derivative Liabilities	0	(5,883)
Total net derivatives	$ 36,919	$ (871)