Commitments and Contingencies - Additional Information (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Financial Instruments With Off Balance Sheet Credit Risk [Line Items]
Commitments to lend additional funds to borrowers	$ 0	$ 100,000
Maximum
Schedule Of Financial Instruments With Off Balance Sheet Credit Risk [Line Items]
Standby letters of credit	14,800,000	17,200,000
Commitments to Extend Credit
Schedule Of Financial Instruments With Off Balance Sheet Credit Risk [Line Items]
Financial instruments with off-balance sheet risks, contract amount	$ 1,110,000,000	$ 1,090,000,000.00