Commitments and Contingencies - Gains (Losses) Related to Interest Rate Derivatives Designated as Hedges of Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Derivative Gains (losses)	$ (214)	$ 128	$ 253
Interest Rate Swaps [Member] | Designated as Fair Value Hedge [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Income [Member]
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Derivative Gains (losses)	(13)	728	(57)
Interest Rate Swaps [Member] | Designated as Fair Value Hedge [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest expense [Member]
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Derivative Gains (losses)	9,380	(3,774)	(200)
Interest Rate Contract [Member] | Designated as Fair Value Hedge [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Income [Member]
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Derivative Gains (losses)	13	(728)	57
Interest Rate Contract [Member] | Designated as Fair Value Hedge [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest expense [Member]
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Derivative Gains (losses)	$ (9,449)	$ 3,805	$ 220