Investment and Equity Securities - Carrying Amounts and Fair Values of Securities Held to Maturity (Detail) - USD ($)	Mar. 31, 2023	Dec. 31, 2022
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity Securities, Amortized Cost	$ 29,227,000	$ 30,306,000
Held-to-maturity Securities, Gross Unrealized Losses	2,631,000	3,128,000
Held-to-maturity Securities, Fair Value	26,596,000	27,178,000
Allowance for credit losses for held to maturity securities	63,000
U.S. Government Agencies [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity Securities, Amortized Cost	143,000	152,000
Held-to-maturity Securities, Gross Unrealized Losses	3,000	5,000
Held-to-maturity Securities, Fair Value	140,000	147,000
Allowance for credit losses for held to maturity securities	0
State and Political Subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity Securities, Amortized Cost	14,084,000	15,154,000
Held-to-maturity Securities, Gross Unrealized Losses	1,199,000	1,775,000
Held-to-maturity Securities, Fair Value	12,885,000	13,379,000
Corporate Bonds [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity Securities, Amortized Cost	15,000,000	15,000,000
Held-to-maturity Securities, Gross Unrealized Losses	1,429,000	1,348,000
Held-to-maturity Securities, Fair Value	13,571,000	$ 13,652,000
Allowance for credit losses for held to maturity securities	$ 63,000