Interest-Bearing Time Deposits in Banks and Securities - Summary of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Securities available-for-sale, Amortized Cost Basis	$ 1,727,237	$ 1,757,442
Securities available-for-sale, Gross Unrealized Holding Gains	92,693	84,393
Securities available-for-sale, Gross Unrealized Holding Losses	(895)	(446)
Securities Available-for-sale, at fair value	1,819,035	1,841,389
Securities held-to-maturity, Amortized Cost Basis	1,061	3,609
Securities held-to-maturity, Gross Unrealized Holding Gains	19	46
Securities held-to-maturity, Gross Unrealized Holding Losses
Securities held-to-maturity, Estimated Fair Value	1,080	3,655
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Securities available-for-sale, Amortized Cost Basis	6,042	15,143
Securities available-for-sale, Gross Unrealized Holding Gains	48	204
Securities available-for-sale, Gross Unrealized Holding Losses
Securities Available-for-sale, at fair value	6,090	15,347
Obligations of U.S. government sponsored-enterprises and agencies [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Securities available-for-sale, Amortized Cost Basis	219,420	255,548
Securities available-for-sale, Gross Unrealized Holding Gains	4,060	5,802
Securities available-for-sale, Gross Unrealized Holding Losses		(4)
Securities Available-for-sale, at fair value	223,480	261,346
Obligations of state and political subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Securities available-for-sale, Amortized Cost Basis	786,278	655,957
Securities available-for-sale, Gross Unrealized Holding Gains	57,541	48,812
Securities available-for-sale, Gross Unrealized Holding Losses	(129)	(98)
Securities Available-for-sale, at fair value	843,690	704,671
Securities held-to-maturity, Amortized Cost Basis	735	3,187
Securities held-to-maturity, Gross Unrealized Holding Gains	7	30
Securities held-to-maturity, Gross Unrealized Holding Losses
Securities held-to-maturity, Estimated Fair Value	742	3,217
Corporate Bonds and Other [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Securities available-for-sale, Amortized Cost Basis	117,244	127,514
Securities available-for-sale, Gross Unrealized Holding Gains	6,020	4,215
Securities available-for-sale, Gross Unrealized Holding Losses	(73)	(255)
Securities Available-for-sale, at fair value	123,191	131,474
Residential mortgage-backed securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Securities available-for-sale, Amortized Cost Basis	564,434	681,277
Securities available-for-sale, Gross Unrealized Holding Gains	23,285	24,247
Securities available-for-sale, Gross Unrealized Holding Losses	(443)	(89)
Securities Available-for-sale, at fair value	587,276	705,435
Securities held-to-maturity, Amortized Cost Basis	294	358
Securities held-to-maturity, Gross Unrealized Holding Gains	11	14
Securities held-to-maturity, Gross Unrealized Holding Losses
Securities held-to-maturity, Estimated Fair Value	305	372
Commercial mortgage-backed securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Securities available-for-sale, Amortized Cost Basis	33,819	22,003
Securities available-for-sale, Gross Unrealized Holding Gains	1,739	1,113
Securities available-for-sale, Gross Unrealized Holding Losses	(250)
Securities Available-for-sale, at fair value	35,308	23,116
Securities held-to-maturity, Amortized Cost Basis	32	64
Securities held-to-maturity, Gross Unrealized Holding Gains	1	2
Securities held-to-maturity, Gross Unrealized Holding Losses
Securities held-to-maturity, Estimated Fair Value	$ 33	$ 66

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details

- Definition

For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

+ References

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+ Details

- Definition

This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

+ References+ Details

- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

+ References+ Details

- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

+ References+ Details