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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	$ 135,108	$ 134,160	$ 402,525	$ 401,125
Interest expense	40,791	42,110	119,550	127,590
Designated as Fair Value Hedge [Member] | Derivative Interest Rate Swaps [Member]
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	116	22	43	544
Interest expense	(84)	(108)	5,748	(382)
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	(116)	(22)	(43)	(544)
Interest expense	$ 45	$ 101	$ (5,755)	$ 380