Investment Securities - Contractual Maturities of Investment Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Due in one year, Amortized Cost	$ 895
Due after one year through five years, Amortized Cost	43,991
Due after five years through ten years, Amortized Cost	111,791
Due after ten years, Amortized Cost	185,574
Total investment securities available for sale, Amortized Cost	957,997
Due in one year, Fair Value	905
Due after one year through five years, Fair Value	44,163
Due after five years through ten years, Fair Value	113,750
Due after ten years, Fair Value	180,825
Total investment securities available for sale, Fair Value	955,270
Residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	567,697
Securities without a single maturity date, Fair Value	568,323
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	48,049
Securities without a single maturity date, Fair Value	$ 47,304

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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