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Disclosure - Note 7 - Loans and Related Allowance for Credit Losses (Details Textual) Sheet http://middlefieldbank.bank/20241231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-details-textual Note 7 - Loans and Related Allowance for Credit Losses (Details Textual) Details http://middlefieldbank.bank/20241231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-tables 67 false false R68.htm 995610 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Primary Segments of the Loan Portfolio (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-primary-segments-of-the-loan-portfolio-details Note 7 - Loans and Related Allowance for Credit Losses - Primary Segments of the Loan Portfolio (Details) Details 68 false false R69.htm 995611 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Allowance for Loan Losses (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-allowance-for-loan-losses-details Note 7 - Loans and Related Allowance for Credit Losses - Allowance for Loan Losses (Details) Details 69 false false R70.htm 995612 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Classes of the Loan Portfolio Summarized by Credit Quality (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-classes-of-the-loan-portfolio-summarized-by-credit-quality-details Note 7 - Loans and Related Allowance for Credit Losses - Classes of the Loan Portfolio Summarized by Credit Quality (Details) Details 70 false false R71.htm 995613 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Collateral-dependent Loans (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-collateraldependent-loans-details Note 7 - Loans and Related Allowance for Credit Losses - Collateral-dependent Loans (Details) Details 71 false false R72.htm 995614 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Past Due Loans (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-past-due-loans-details Note 7 - Loans and Related Allowance for Credit Losses - Past Due Loans (Details) Details 72 false false R73.htm 995615 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Nonaccrual Loans (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-nonaccrual-loans-details Note 7 - Loans and Related Allowance for Credit Losses - Nonaccrual Loans (Details) Details 73 false false R74.htm 995616 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Troubled Debt Restructurings (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-troubled-debt-restructurings-details Note 7 - Loans and Related Allowance for Credit Losses - 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Disclosure - Note 9 - Goodwill and Intangible Assets - Goodwill (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-9-goodwill-and-intangible-assets-goodwill-details Note 9 - Goodwill and Intangible Assets - Goodwill (Details) Details 78 false false R79.htm 995621 - Disclosure - Note 9 - Goodwill and Intangible Assets - Estimated Aggregate Future Amortization Expense for Core Deposit Intangible Assets (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-9-goodwill-and-intangible-assets-estimated-aggregate-future-amortization-expense-for-core-deposit-intangible-assets-details Note 9 - Goodwill and Intangible Assets - Estimated Aggregate Future Amortization Expense for Core Deposit Intangible Assets (Details) Details 79 false false R80.htm 995622 - Disclosure - Note 9 - Goodwill and Intangible Assets - Activity for Mortgage Servicing Rights (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-9-goodwill-and-intangible-assets-activity-for-mortgage-servicing-rights-details Note 9 - Goodwill and Intangible Assets - Activity for Mortgage Servicing Rights (Details) Details 80 false false R81.htm 995623 - Disclosure - Note 10 - Deposits (Details Textual) Sheet http://middlefieldbank.bank/20241231/role/statement-note-10-deposits-details-textual Note 10 - Deposits (Details Textual) Details http://middlefieldbank.bank/20241231/role/statement-note-10-deposits-tables 81 false false R82.htm 995624 - Disclosure - Note 10 - Deposits - Scheduled Maturities of Time Deposits (Details) Sheet http://middlefieldbank.bank/20241231/role/statement-note-10-deposits-scheduled-maturities-of-time-deposits-details Note 10 - Deposits - Scheduled Maturities of Time Deposits (Details) Details 82 false false R83.htm 995625 - Disclosure - Note 11 - Short-term Borrowings (Details Textual) Sheet http://middlefieldbank.bank/20241231/role/statement-note-11-shortterm-borrowings-details-textual Note 11 - Short-term Borrowings (Details Textual) Details http://middlefieldbank.bank/20241231/role/statement-note-11-shortterm-borrowings-tables 83 false false R84.htm 995626 - 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