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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	$ 158,164	$ 136,338	$ 308,646	$ 267,417
Interest expense	39,577	39,745	78,476	78,759
Derivatives Designated as Hedging Instruments | Designated as Fair Value Hedge
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	(157)	49	(103)	73
Interest expense	3,840	(2,859)	1,059	(5,800)
Interest Rate Swaps | Designated as Fair Value Hedge
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income	157	(49)	103	(73)
Interest expense	$ (3,832)	$ 2,856	$ (1,091)	$ 5,832