Investment Securities (Amortized Cost and Fair Value of Total Debt Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule Of Available For Sale Securities [Line Items]
Securities available for sale, Within one year - Amortized Cost	$ 9,546	$ 8,690
Securities available for sale, After one year but within five years - Amortized Cost	85,458	141,362
Securities available for sale, After five years but within ten years - Amortized Cost	835,879	935,796
Securities available for sale, After ten years - Amortized Cost	1,390,443	1,410,879
Securities available for sale - Amortized Cost	2,321,326	2,496,727
Securities available for sale, Within one year - Fair Value	9,719	8,781
Securities available for sale, After one year but within five years - Fair Value	86,471	143,714
Securities available for sale, After five years but within ten years - Fair Value	833,557	952,680
Securities available for sale, After ten years - Fair Value	1,390,028	1,448,207
Securities available for sale - Fair Value	$ 2,319,775	$ 2,553,382

Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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