Securities - Components of Available for Sale Portfolio (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 354,312	$ 361,503
Available-for-sale securities, Gross unrealized gains	12,890	406
Available-for-sale securities, Gross unrealized losses		(4,239)
Total fair value	367,202	357,670
U.S. Treasury and Government Sponsored Entities' Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	193,513	221,500
Available-for-sale securities, Gross unrealized gains	8,263	159
Available-for-sale securities, Gross unrealized losses		(3,009)
Total fair value	201,776	218,650
States of the U.S. and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	49,534	10,848
Available-for-sale securities, Gross unrealized gains	2,473	192
Total fair value	52,007	11,040
Mortgage-Backed GSE Securities: Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	111,265	129,155
Available-for-sale securities, Gross unrealized gains	2,154	55
Available-for-sale securities, Gross unrealized losses		(1,230)
Total fair value	$ 113,419	$ 127,980