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Loans and Allowance for Loan Losses - Additional Information (Details) $ in Thousands | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2021 USD ($) Loan Borrower | Sep. 30, 2021 USD ($) Loan Borrower | Sep. 30, 2021 USD ($) Loan Borrower | Sep. 30, 2021 USD ($) Loan Borrower | Sep. 30, 2021 USD ($) Loan Borrower Contract | Sep. 30, 2021 USD ($) Loan Borrower DebtSecurityNumber | Dec. 31, 2020 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2020 USD ($) Loan | Dec. 31, 2020 USD ($) Contract | Dec. 31, 2020 USD ($) DebtSecurityNumber | Sep. 30, 2020 USD ($) | Dec. 31, 2019 USD ($)
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Loans Pledged as Collateral | $ 62,700 | $ 62,700 | $ 62,700 | $ 62,700 | $ 62,700 | $ 62,700 | $ 36,100 | $ 36,100 | $ 36,100 | $ 36,100 | $ 36,100 |  |
Loans and Leases Receivable, Related Parties, Ending Balance |  | 300 |  |  |  |  | 400 |  |  |  |  |  |
Loans and Leases Receivable, Related Parties, Additions |  | 0 |  |  |  |  | 0 |  |  |  |  |  |
Loans and Leases Receivable, Related Parties, Proceeds |  | 100 |  |  |  |  | 500 |  |  |  |  |  |
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest | 1,000 | 1,000 | 1,000 | 1,000 | 1,000 | 1,000 | 3,100 | 3,100 | 3,100 | 3,100 | 3,100 |  |
Financing Receivable, Troubled Debt Restructuring | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 |  |
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans |  | 44 |  |  |  |  | 161 |  |  |  |  |  |
Interest Income Recorded | 9 | 9 | 9 | $ 9 | 9 | $ 9 | 42 | 42 | $ 42 | 42 | $ 42 |  |
Number of loans |  |  |  | 2 |  | 7 |  |  | 0 |  | 5 |  |
Financing Receivable, Restructuring Recorded Investment With Nonaccrual Status | 6,500 | 6,500 | 6,500 | $ 6,500 | 6,500 | $ 6,500 |  |  |  |  |  |  |
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Cash Flows Expected to be Collected at Acquisition | 0 | 0 | 0 | 0 | $ 0 | 0 | 0 | 0 | $ 0 | $ 0 | $ 0 |  |
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts | Contract |  |  |  |  | 0 |  |  |  |  | 0 |  |  |
Loans, allowance for loan losses | 8,193 | 8,193 | 8,193 | 8,193 | $ 8,193 | 8,193 | 7,470 | 7,470 | 7,470 | $ 7,470 | 7,470 | $ 7,185 | $ 5,762
Restructured Loan Modified through Extended Maturity and Payment Schedule Modification [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Financing Receivable, Restructuring Recorded Investment With Nonaccrual Status | 500 | 500 | 500 | 500 | 500 | 500 |  |  |  |  |  |  |
Loans, allowance for loan losses | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Loans Modified in a Troubled Debt Restructuring, Individually Evaluated for Impairment, Principal Balance, Threshold | 500 | 500 | 500 | 500 | 500 | 500 |  |  |  |  |  |  |
Minimum [Member] | ALC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest | $ 50 | $ 50 | $ 50 | $ 50 | $ 50 | $ 50 |  |  |  |  |  |  |
Paycheck Protection Program [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Loan, fixed interest rate | 1.00% | 1.00% | 1.00% | 1.00% | 1.00% | 1.00% |  |  |  |  |  |  |
Loan, aggregate principal balance | $ 3,900 | $ 3,900 | $ 3,900 | $ 3,900 | $ 3,900 | $ 3,900 |  |  |  |  |  |  |
Number of loans to small businesses | Loan | 77 | 77 | 77 | 77 | 77 | 77 |  |  |  |  |  |  |
Number of companies | Borrower | 194 | 194 | 194 | 194 | 194 | 194 |  |  |  |  |  |  |
Amortized loan fees |  | $ 398 |  |  |  |  | 161 |  |  |  |  |  |
Net deferred loan fee |  | $ 188 |  |  |  |  |  |  |  |  |  |  |
Paycheck Protection Program [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Loan fee percentage | 1.00% | 1.00% | 1.00% | 1.00% | 1.00% | 1.00% |  |  |  |  |  |  |
Paycheck Protection Program [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Loan fee percentage | 5.00% | 5.00% | 5.00% | 5.00% | 5.00% | 5.00% |  |  |  |  |  |  |
Paycheck Protection Program [Member] | Two Year Term Loan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Loan, aggregate principal balance | $ 200 | $ 200 | $ 200 | $ 200 | $ 200 | $ 200 |  |  |  |  |  |  |
Loan payment term | two-year |  |  |  |  |  |  |  |  |  |  |  |
Paycheck Protection Program [Member] | Five Year Term Loan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Loan, aggregate principal balance | $ 3,700 | 3,700 | 3,700 | 3,700 | 3,700 | 3,700 |  |  |  |  |  |  |
Loan payment term | five-year |  |  |  |  |  |  |  |  |  |  |  |
Financial Asset Acquired With Credit Deterioration [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Amount Of Deferment Loan | $ 800 | 800 | $ 800 | $ 800 | $ 800 | $ 800 | 8,100 | $ 8,100 | $ 8,100 | $ 8,100 | $ 8,100 |  |
Deferred principal balance of loan reduced |  | $ 11,600 |  |  |  |  | $ 13,500 |  |  |  |  |  |
Deferred principal balance of loan reduced percentage |  |  | 1.60% |  |  |  |  | 2.10% |  |  |  |  |
Real Estate [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of Loan Portfolio | 53.80% | 53.80% | 53.80% | 53.80% | 53.80% | 53.80% | 56.10% | 56.10% | 56.10% | 56.10% | 56.10% |  |

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