Securities - Securities Available for Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 422,717	$ 409,110
Unrealized Gains	3,212	4,798
Unrealized Losses	(7,630)	(4,199)
Fair Value	418,299	409,709
U.S. Government Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	113,341	108,578
Unrealized Gains	334	478
Unrealized Losses	(1,754)	(908)
Fair Value	111,921	108,148
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	131,608	134,428
Unrealized Gains	2,616	3,609
Unrealized Losses	(758)	(314)
Fair Value	133,466	137,723
Residential and Multi-Family Mortgage [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	123,995	111,214
Unrealized Gains	104	304
Unrealized Losses	(3,469)	(1,882)
Fair Value	120,630	109,636
Corporate Notes and Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,608	17,610
Unrealized Gains	45	52
Unrealized Losses	(459)	(462)
Fair Value	17,194	17,200
Pooled SBA [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	35,145	36,260
Unrealized Gains	113	355
Unrealized Losses	(1,113)	(575)
Fair Value	34,145	36,040
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,020	1,020
Unrealized Gains	0	0
Unrealized Losses	(77)	(58)
Fair Value	$ 943	$ 962