Investment Securities - Contractual Maturities of Investments Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Due in one year, Amortized Cost	$ 851
Due after one year through five years, Amortized Cost	6,140
Due after five years through ten years, Amortized Cost	95,454
Due after ten years, Amortized Cost	155,028
Total investment securities available for sale, Amortized Cost	813,474
Due in one year, Fair Value	865
Due after one year through five years, Fair Value	6,246
Due after five years through ten years, Fair Value	97,354
Due after ten years, Fair Value	143,689
Total investment securities available for sale, Fair Value	807,816
Residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	506,695
Securities without a single maturity date, Fair Value	510,154
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities without a single maturity date, Amortized Cost	49,306
Securities without a single maturity date, Fair Value	$ 49,508

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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