Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 957,997	$ 813,474
Gross Unrealized Gains	16,631	13,821
Gross Unrealized Losses	(19,358)	(19,479)
Fair Value	955,270	807,816
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,841	99,843
Gross Unrealized Gains
Gross Unrealized Losses	(4,383)	(2,218)
Fair Value	95,458	97,625
U.S. government agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	57,400	44,215
Gross Unrealized Gains	1,597	1,547
Gross Unrealized Losses	(7)
Fair Value	58,990	45,762
Obligations of states and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,513	16,210
Gross Unrealized Gains	738	417
Gross Unrealized Losses	(632)
Fair Value	42,619	16,627
Residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	567,697	506,695
Gross Unrealized Gains	5,634	6,818
Gross Unrealized Losses	(5,008)	(3,359)
Fair Value	568,323	510,154
Trust preferred securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	68,902	68,931
Gross Unrealized Gains	4,843	240
Gross Unrealized Losses	(7,416)	(11,739)
Fair Value	66,329	57,432
Corporate and other debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	73,595	28,274
Gross Unrealized Gains	2,883	2,728
Gross Unrealized Losses	(231)	(294)
Fair Value	76,247	30,708
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,049	49,306
Gross Unrealized Gains	936	2,071
Gross Unrealized Losses	(1,681)	(1,869)
Fair Value	$ 47,304	$ 49,508

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