Investment Securities - Contractual Maturities of Debt Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Due in one year, Amortized Cost	$ 113,890
Due after one year through five years, Amortized Cost	41,597
Due after five years through ten years, Amortized Cost	239,769
Due after ten years, Amortized Cost	390,804
Residential mortgage-backed securities, Amortized Cost	813,647
Total investment securities held to maturity, Amortized Cost	1,599,707
Due in one year, Fair Value	113,941
Due after one year through five years, Fair Value	43,810
Due after five years through ten years, Fair Value	266,844
Due after ten years, Fair Value	395,239
Residential mortgage-backed securities, Fair Value	838,116
Total investment securities held to maturity, Fair Value	$ 1,657,950

Amount of held-to-maturity debt securities at fair value maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year.

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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing in the fifth through tenth fiscal year following the latest fiscal year.

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Amount of held-to-maturity debt securities at fair value maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year.

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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing in the next fiscal year through the fifth fiscal year following the latest fiscal year.

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Amount of held-to-maturity debt securities at fair value maturing after the tenth fiscal year following the latest fiscal year.

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This item represents the total of all debt securities grouped by maturity dates, at fair value, which are categorized as held-to-maturity.

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Amount of held-to-maturity debt securities at fair value maturing in the next fiscal year following the latest fiscal year.

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Amount of held-to-maturity debt securities at fair value that do not have a single maturity date and which the entity has decided to disclose separately rather than allocating the fair value over several maturity groupings.

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