Securities - Gross Unrealized Losses, Aggregated by Investment Category and Length of Time (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months	$ (140)	$ (238)
Fair Value, Less Than Twelve Months	51,893	55,090
Gross Unrealized Losses, Twelve Months and Over		(142)
Fair Value, Twelve Months and Over		27,107
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Twelve Months and Over		(12)
Fair Value, Twelve Months and Over		5,030
U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months	(130)	(16)
Fair Value, Less Than Twelve Months	48,331	10,549
Gross Unrealized Losses, Twelve Months and Over		(5)
Fair Value, Twelve Months and Over		10,745
Mortgage-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months		(102)
Fair Value, Less Than Twelve Months		27,696
Gross Unrealized Losses, Twelve Months and Over		(125)
Fair Value, Twelve Months and Over		11,332
State and Local Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses, Less Than Twelve Months	(10)	(120)
Fair Value, Less Than Twelve Months	$ 3,562	$ 16,845