Securities Available for Sale - Amortized Cost and Fair Values of Investment Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 402,431
Fair Value	402,500
Equity securities, Amortized Cost	50
Equity securities, Fair Value	63
Available for sale securities, Total	402,481	414,348
Available for sale securities, Gross Unrealized Gains	3,464	1,621
Available for sale securities, Gross Unrealized Losses	3,382	9,026
Securities available for sale	402,563	406,943
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	402,431	414,298
Gross Unrealized Gains	3,451	1,602
Gross Unrealized Losses	3,382	9,026
Fair Value	402,500	406,874
Debt Securities [Member] \| U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,216	25,610
Gross Unrealized Gains	15	34
Gross Unrealized Losses	55	193
Fair Value	24,176	25,451
Debt Securities [Member] \| U.S. government sponsored enterprises (GSE) [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		14,431
Gross Unrealized Gains		5
Gross Unrealized Losses		722
Fair Value		13,714
Debt Securities [Member] \| States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	52,658	75,494
Gross Unrealized Gains	726	417
Gross Unrealized Losses	1,370	4,367
Fair Value	52,014	71,544
Debt Securities [Member] \| GSE Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	178,817	198,449
Gross Unrealized Gains	1,456	895
Gross Unrealized Losses	487	725
Fair Value	179,786	198,619
Debt Securities [Member] \| GSE Residential Collateralized Mortgage Obligations (CMOs) [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	81,584	40,502
Gross Unrealized Gains	788	251
Gross Unrealized Losses	388	221
Fair Value	81,984	40,532
Debt Securities [Member] \| GSE Commercial CMOs [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	65,156	59,812
Gross Unrealized Gains	466	0
Gross Unrealized Losses	1,082	2,798
Fair Value	64,540	57,014
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity securities, Amortized Cost	50	50
Equity securities, Gross Unrealized Gains	13	19
Equity securities, Gross Unrealized Losses	0	0
Equity securities, Fair Value	$ 63	$ 69

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

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

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