Securities - Securities Available for Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 409,110	$ 493,691
Unrealized Gains	4,798	7,683
Unrealized Losses	(4,199)	(5,539)
Fair Value	409,709	495,835
U.S. Government Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	108,578	139,823
Unrealized Gains	478	1,107
Unrealized Losses	(908)	(579)
Fair Value	108,148	140,351
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	134,428	153,492
Unrealized Gains	3,609	4,194
Unrealized Losses	(314)	(649)
Fair Value	137,723	157,037
Residential and Multi-Family Mortgage [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	111,214	136,807
Unrealized Gains	304	551
Unrealized Losses	(1,882)	(2,382)
Fair Value	109,636	134,976
Corporate Notes and Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,610	18,299
Unrealized Gains	52	77
Unrealized Losses	(462)	(962)
Fair Value	17,200	17,414
Pooled Trust Preferred [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	800
Unrealized Gains	0	1,249
Unrealized Losses	0	0
Fair Value	0	2,049
Pooled SBA [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	36,260	43,450
Unrealized Gains	355	505
Unrealized Losses	(575)	(918)
Fair Value	36,040	43,037
Other Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,020	1,020
Unrealized Gains	0	0
Unrealized Losses	(58)	(49)
Fair Value	$ 962	$ 971