Securities - Components of Available for Sale Portfolio (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 339,164	$ 348,099
Available-for-sale securities, Gross unrealized gains	305	225
Available-for-sale securities, Gross unrealized losses	(3,635)	(5,040)
Available-for-sale securities, Total fair value	335,834	343,284
U.S. Treasury and Government Sponsored Entities' Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	182,855	188,082
Available-for-sale securities, Gross unrealized gains	234	172
Available-for-sale securities, Gross unrealized losses	(1,436)	(2,221)
Available-for-sale securities, Total fair value	181,653	186,033
States of the U.S. and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	59,264	59,415
Available-for-sale securities, Gross unrealized gains	10	3
Available-for-sale securities, Gross unrealized losses	(1,410)	(1,661)
Available-for-sale securities, Total fair value	57,864	57,757
Mortgage-Backed GSE Securities: Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	97,045	100,602
Available-for-sale securities, Gross unrealized gains	61	50
Available-for-sale securities, Gross unrealized losses	(789)	(1,158)
Available-for-sale securities, Total fair value	$ 96,317	$ 99,494