Off Balance Sheet Activities - Outstanding Financial Instruments Whose Contract Amounts Represent Credit Risk (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Standby letters of credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Concentration of Risk	$ 2,021	$ 1,345
Commitments to extend credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Concentration of Risk	456,299	394,437
Credit card arrangements [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Concentration of Risk	$ 22,903	$ 20,695