Securities - Unrealized Loss Positions (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	$ 31,527	$ 28,304
Less than 12 months, Unrealized Loss	(730)	(370)
12 months or more, Fair Value	38,659	21,971
12 months or more, Unrealized Loss	(1,848)	(474)
Fair Value, Total	70,186	50,275
Total Unrealized Loss	(2,578)	(844)
US Government Agencies Agencies and Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	17,047	25,053
Less than 12 months, Unrealized Loss	(498)	(353)
12 months or more, Fair Value	32,892	16,184
12 months or more, Unrealized Loss	(1,440)	(334)
Fair Value, Total	49,939	41,237
Total Unrealized Loss	(1,938)	(687)
State and Municipal Obligations
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	11,996	2,753
Less than 12 months, Unrealized Loss	(191)	(15)
12 months or more, Fair Value	5,767	5,787
12 months or more, Unrealized Loss	(408)	(140)
Fair Value, Total	17,763	8,540
Total Unrealized Loss	(599)	(155)
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	2,484	498
Less than 12 months, Unrealized Loss	(41)	(2)
Fair Value, Total	2,484	498
Total Unrealized Loss	$ (41)	$ (2)