Derivative Financial Instruments (Schedule of outstanding interest rate swaps and caps not designated for hedge accounting) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Total Notional Amount	$ 8,118,631	$ 13,138,667
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Gain	5,408	17,062
Derivative Asset, Loss	(34,784)	(23,087)
Not Designated as Hedging Instrument [Member] | Customer Position [Member]
Derivative [Line Items]
Number of Instruments	285	235
Total Notional Amount	2,118,694	1,563,728
Derivative Asset, Gain	48,209	29,004
Derivative Liability, Loss	(2,539)	(11,175)
Net	45,670	17,829
Not Designated as Hedging Instrument [Member] | Customer Position [Member] | Other Assets [Member] | Commercial loan interest rate derivatives [Member]
Derivative [Line Items]
Number of Instruments	224	159
Total Notional Amount	1,537,395	915,272
Derivative Asset, Gain	48,209	29,004
Derivative Asset, Loss	0	0
Net	48,209	29,004
Not Designated as Hedging Instrument [Member] | Customer Position [Member] | Other Liabilities [Member] | Commercial loan interest rate derivatives [Member]
Derivative [Line Items]
Number of Instruments	61	76
Total Notional Amount	581,299	648,456
Derivative Liability, Gain	0	0
Derivative Liability, Loss	(2,539)	(11,175)
Net	(2,539)	(11,175)
Not Designated as Hedging Instrument [Member] | Counterparty Position [Member]
Derivative [Line Items]
Number of Instruments	283	243
Total Notional Amount	7,718,631	12,763,667
Derivative Asset, Gain	5,408	17,094
Derivative Liability, Loss	(34,784)	(23,119)
Net	(29,376)	(6,025)
Not Designated as Hedging Instrument [Member] | Counterparty Position [Member] | Other Assets [Member] | Commercial loan interest rate derivatives [Member]
Derivative [Line Items]
Number of Instruments	0	111
Total Notional Amount	0	914,044
Derivative Asset, Gain	0	8,944
Derivative Asset, Loss	0	(2,766)
Net	0	6,178
Not Designated as Hedging Instrument [Member] | Counterparty Position [Member] | Other Liabilities [Member] | Commercial loan interest rate derivatives [Member]
Derivative [Line Items]
Number of Instruments	276	118
Total Notional Amount	2,118,631	649,623
Derivative Liability, Gain	5,408	8,118
Derivative Liability, Loss	(34,491)	(20,094)
Net	(29,083)	(11,976)
Not Designated as Hedging Instrument [Member] | Counterparty Position [Member] | Other Liabilities [Member] | Fed Funds futures [Member]
Derivative [Line Items]
Number of Instruments	7	14
Total Notional Amount	5,600,000	11,200,000
Derivative Liability, Gain	0	32
Derivative Liability, Loss	(293)	(259)
Net	$ (293)	$ (227)