Derivative Instruments and Hedging Activities - Gains (Losses) Related to Interest Rate Derivatives Designated as Hedges of Fair Value (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	$ 157,141	$ 135,108	$ 465,787	$ 402,525
Interest expense	40,730	40,791	119,206	119,550
Derivatives Designated as Hedging Instruments | Designated as Fair Value Hedge
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	93	(116)	(10)	(43)
Interest expense	(4,329)	45	(3,270)	(5,755)
Interest Rate Swaps | Designated as Fair Value Hedge
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	(93)	116	10	43
Interest expense	$ 4,302	$ (84)	$ 3,211	$ 5,748