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Borrowings - Additional Information (Detail) - USD ($)
9 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Sep. 30, 2020
Line of Credit Facility [Line Items]      
Revolving line of credit, permitted $ 25,000,000    
Line of credit $ 0 $ 0 $ 0
Line of credit, maturity date Jun. 30, 2021    
Federal Home Loan Bank Borrowings [Member]      
Line of Credit Facility [Line Items]      
Line of credit $ 0