Contractual Maturities of Debt Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Due in one year, Amortized Value	$ 109,488
Due after one year through five years, Amortized Value	43,154
Due after five years through ten years, Amortized Value	240,982
Due after ten years, Amortized Value	378,576
Residential mortgage-backed securities, Amortized Value	852,375
Total investment securities held to maturity, Amortized Value	1,624,575
Due in one year, Fair Value	109,564
Due after one year through five years, Fair Value	44,797
Due after five years through ten years, Fair Value	267,688
Due after ten years, Fair Value	381,208
Residential mortgage-backed securities, Fair Value	886,156
Total investment securities held to maturity, Fair Value	$ 1,689,413

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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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 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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