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Loan Servicing - Loan Servicing Rights - Additional Information (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Loan Servicing      
Carrying amount/fair value $ 1,172,000 $ 1,295,000 $ 1,651,000
Prepayment speed assumption (annual rate) (as a percent) 14.65% 13.50% 10.89%
Residual cash flow discount rate assumption (annual) (as a percent) 12.91% 15.90% 16.40%
Loan servicing rights      
Loan Servicing      
Valuation allowance $ 0 $ 0 $ 0