Debt and Equity Securities - Summary of Debt and Equity Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Summary Of Debt And Equity Securities [Line Items]
Available-for-sale, Amortized Cost	$ 292,613	$ 347,520
Available-for-sale, Gross Unrealized Gains	1,336	1,056
Available-for-sale, Gross Unrealized Losses	898	2,156
Available-for-sale, Estimated Market Value	293,051	346,420
Held-To-Maturity Securities, Amortized Cost	25,790	28,123
Held-To-Maturity Securities, Gross Unrealized Gains	332	465
Held-To-Maturity Securities, Gross Unrealized Losses	164	188
Held-To-Maturity Securities, Estimated Market Value	25,958	28,400
US Government-Sponsored Enterprises (GSEs) and Agency-Backed Securities [Member]
Summary Of Debt And Equity Securities [Line Items]
Available-for-sale, Amortized Cost	94,160	131,767
Available-for-sale, Gross Unrealized Gains	403	129
Available-for-sale, Gross Unrealized Losses	276	1,329
Available-for-sale, Estimated Market Value	94,287	130,567
Government- Sponsored Enterprises (GSEs) Residential Mortgage Backed [Member]
Summary Of Debt And Equity Securities [Line Items]
Available-for-sale, Amortized Cost	147,488	170,802
Available-for-sale, Gross Unrealized Gains	629	731
Available-for-sale, Gross Unrealized Losses	471	464
Available-for-sale, Estimated Market Value	147,646	171,069
Held-To-Maturity Securities, Amortized Cost	6,745	7,398
Held-To-Maturity Securities, Gross Unrealized Gains	62	76
Held-To-Maturity Securities, Gross Unrealized Losses	135	147
Held-To-Maturity Securities, Estimated Market Value	6,672	7,327
SBAP [Member]
Summary Of Debt And Equity Securities [Line Items]
Available-for-sale, Amortized Cost	27,723	30,627
Available-for-sale, Gross Unrealized Gains	137	98
Available-for-sale, Gross Unrealized Losses	37	205
Available-for-sale, Estimated Market Value	27,823	30,520
Obligations of States and Political Subdivisions [Member]
Summary Of Debt And Equity Securities [Line Items]
Available-for-sale, Amortized Cost	23,242	14,324
Available-for-sale, Gross Unrealized Gains	167	98
Available-for-sale, Gross Unrealized Losses	114	158
Available-for-sale, Estimated Market Value	23,295	14,264
Held-To-Maturity Securities, Amortized Cost	19,045	20,725
Held-To-Maturity Securities, Gross Unrealized Gains	270	389
Held-To-Maturity Securities, Gross Unrealized Losses	29	41
Held-To-Maturity Securities, Estimated Market Value	$ 19,286	$ 21,073