Derivative Instruments and Hedging Activities - Gains (Losses) Related to Interest Rate Derivatives Designated as Hedges of Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	$ 150,482	$ 131,079
Interest expense	38,899	39,014
Designated as Fair Value Hedge [Member] | Derivatives Designated as Hedging Instruments [Member]
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	54	23
Interest expense	(2,781)	3,144
Interest Rate Swaps [Member] | Designated as Fair Value Hedge [Member]
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	(54)	(23)
Interest expense	$ 2,741	$ (3,175)