Securities Available for Sale - Amortized Cost and Fair Values of Investment Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 344,359
Fair Value	349,759
Equity securities, Amortized Cost	50
Equity securities, Fair Value	68
Available for sale securities, Total	344,409	373,775
Available for sale securities, Gross Unrealized Gains	5,994	4,354
Available for sale securities, Gross Unrealized Losses	576	1,930
Securities available for sale	349,827us-gaap_AvailableForSaleSecurities	376,199us-gaap_AvailableForSaleSecurities
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	344,359	373,725
Gross Unrealized Gains	5,976	4,337
Gross Unrealized Losses	576	1,930
Fair Value	349,759	376,132
Debt Securities \| U.S. Government Agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28,282	23,910
Gross Unrealized Gains	97	71
Gross Unrealized Losses	29	23
Fair Value	28,350	23,958
Debt Securities \| States and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	57,826	52,578
Gross Unrealized Gains	1,046	819
Gross Unrealized Losses	393	996
Fair Value	58,479	52,401
Debt Securities \| GSE residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		174,220
Gross Unrealized Gains		1,573
Gross Unrealized Losses		197
Fair Value		175,596
Debt Securities \| U.S. Government Sponsored Enterprises (GSE) residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	158,610
Gross Unrealized Gains	2,599
Gross Unrealized Losses	0
Fair Value	161,209
Debt Securities \| GSE residential collateralized mortgage obligations (CMOs)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30,071	57,976
Gross Unrealized Gains	492	857
Gross Unrealized Losses	85	128
Fair Value	30,478	58,705
Debt Securities \| GSE commercial CMOs
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	69,570	65,041
Gross Unrealized Gains	1,742	1,017
Gross Unrealized Losses	69	586
Fair Value	71,243	65,472
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Equity securities, Amortized Cost	50	50
Equity securities, Gross Unrealized Gains	18	17
Equity securities, Gross Unrealized Losses	0	0
Equity securities, Fair Value	$ 68	$ 67

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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