Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 817,125	$ 889,958
Gross Unrealized Gains	6,015	9,343
Gross Unrealized Losses	(15,566)	(12,331)
Fair Value	807,574	886,970
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	51,052	51,063
Gross Unrealized Gains	7	2
Gross Unrealized Losses	(1,786)	(1,622)
Fair Value	49,273	49,443
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	25,862	33,163
Gross Unrealized Gains	667	748
Gross Unrealized Losses	0	(86)
Fair Value	26,529	33,825
Obligations of states and state agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	11,040	11,160
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(106)	(24)
Fair Value	10,934	11,136
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	33,323	33,340
Gross Unrealized Gains	40	127
Gross Unrealized Losses	(887)	(552)
Fair Value	32,476	32,915
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	44,363	44,500
Gross Unrealized Gains	40	127
Gross Unrealized Losses	(993)	(576)
Fair Value	43,410	44,051
Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	591,342	643,382
Gross Unrealized Gains	3,184	5,854
Gross Unrealized Losses	(8,735)	(4,960)
Fair Value	585,791	644,276
Trust preferred securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	10,587	23,194
Gross Unrealized Gains	0	296
Gross Unrealized Losses	(1,969)	(2,953)
Fair Value	8,618	20,537
Corporate and other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	72,897	73,585
Gross Unrealized Gains	1,428	1,645
Gross Unrealized Losses	(841)	(1,218)
Fair Value	73,484	74,012
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	21,022	21,071
Gross Unrealized Gains	689	671
Gross Unrealized Losses	(1,242)	(916)
Fair Value	$ 20,469	$ 20,826

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

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-Name Accounting Standards Codification

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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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.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

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