Securities - Gross Unrealized Losses, Aggregated by Investment Category and Length of Time (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months	$ (1)	$ (26)
Fair Value, Less Than Twelve Months	720	3,951
Gross Unrealized Losses, Twelve Months and Over	(2,570)	(4,085)
Fair Value, Twelve Months and Over	143,640	145,348
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Twelve Months and Over	(182)	(254)
Fair Value, Twelve Months and Over	20,908	20,861
U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Twelve Months and Over	(1,205)	(1,910)
Fair Value, Twelve Months and Over	65,412	64,727
Mortgage-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months	(1)	(4)
Fair Value, Less Than Twelve Months	720	697
Gross Unrealized Losses, Twelve Months and Over	(821)	(1,138)
Fair Value, Twelve Months and Over	29,528	30,347
State and Local Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months		(22)
Fair Value, Less Than Twelve Months		3,254
Gross Unrealized Losses, Twelve Months and Over	(362)	(783)
Fair Value, Twelve Months and Over	$ 27,792	$ 29,413