Investment Securities - Summary of Securities with Gross Unrealized Losses (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses, Less than Twelve Months	$ (91)	$ (132)
Fair Value, Less than Twelve Months	10,390	10,045
Gross Unrealized Losses, Twelve Months and Over	(122)	(1,017)
Fair Value, Twelve Months and Over	7,678	31,130
Mortgage-backed Securities, Principally Obligations of US Federal Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses, Less than Twelve Months	(74)	(54)
Fair Value, Less than Twelve Months	8,291	4,616
Gross Unrealized Losses, Twelve Months and Over	(38)	(688)
Fair Value, Twelve Months and Over	4,939	24,871
State and Municipalities [Member]
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Losses, Less than Twelve Months	(17)	(78)
Fair Value, Less than Twelve Months	2,099	5,429
Gross Unrealized Losses, Twelve Months and Over	(84)	(329)
Fair Value, Twelve Months and Over	$ 2,739	$ 6,259