Contractual Maturities of Investments Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Due in one year, Amortized Cost	$ 940
Due after one year through five years, Amortized Cost	2,117
Due after five years through ten years, Amortized Cost	50,960
Due after ten years, Amortized Cost	109,559
Total investment securities available for sale, Amortized Cost	677,371
Due in one year, Fair Value	958
Due after one year through five years, Fair Value	2,134
Due after five years through ten years, Fair Value	53,464
Due after ten years, Fair Value	97,475
Total investment securities available for sale, Fair Value	673,911
Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	463,489
Securities without a single maturity date, Fair Value	470,727
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	50,306
Securities without a single maturity date, Fair Value	$ 49,153

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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