Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 799,264	$ 889,958
Gross Unrealized Gains	8,974	9,343
Gross Unrealized Losses	(10,849)	(12,331)
Fair Value	797,389	886,970
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	51,047	51,063
Gross Unrealized Gains	20	2
Gross Unrealized Losses	(599)	(1,622)
Fair Value	50,468	49,443
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	24,738	33,163
Gross Unrealized Gains	779	748
Gross Unrealized Losses	(4)	(86)
Fair Value	25,513	33,825
Obligations of states and state agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	10,980	11,160
Gross Unrealized Gains	22	0
Gross Unrealized Losses	0	(24)
Fair Value	11,002	11,136
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	33,215	33,340
Gross Unrealized Gains	60	127
Gross Unrealized Losses	(808)	(552)
Fair Value	32,467	32,915
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	44,195	44,500
Gross Unrealized Gains	82	127
Gross Unrealized Losses	(808)	(576)
Fair Value	43,469	44,051
Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	569,182	643,382
Gross Unrealized Gains	5,865	5,854
Gross Unrealized Losses	(5,397)	(4,960)
Fair Value	569,650	644,276
Trust preferred securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	10,530	23,194
Gross Unrealized Gains	0	296
Gross Unrealized Losses	(1,937)	(2,953)
Fair Value	8,593	20,537
Corporate and other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	78,550	73,585
Gross Unrealized Gains	1,413	1,645
Gross Unrealized Losses	(946)	(1,218)
Fair Value	79,017	74,012
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	21,022	21,071
Gross Unrealized Gains	815	671
Gross Unrealized Losses	(1,158)	(916)
Fair Value	$ 20,679	$ 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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