Investment Securities (Amortized Cost and Fair Value of Total Debt Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Disclosure Investment Securities Amortized Cost And Fair Value Of Total Debt Securities [Abstract]
Securities available for sale, Within one year - Amortized Cost	$ 6,068	$ 8,690
Securities available for sale, After one year but within five years - Amortized Cost	105,652	141,362
Securities available for sale, After five years but within ten years - Amortized Cost	970,915	935,796
Securities available for sale, After ten years - Amortized Cost	1,375,233	1,410,879
Securities available for sale - Amortized Cost	2,457,868	2,496,727
Securities available for sale, Within one year - Fair Value	6,230	8,781
Securities available for sale, After one year but within five years - Fair Value	106,773	143,714
Securities available for sale, After five years but within ten years - Fair Value	975,745	952,680
Securities available for sale, After ten years - Fair Value	1,370,894	1,448,207
Securities available for sale - Fair Value	$ 2,459,642	$ 2,553,382