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Disclosure - Note 7 - Loans and Related Allowance for Credit Losses (Tables) Sheet http://middlefieldbank.bank/20231231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-tables Note 7 - Loans and Related Allowance for Credit Losses (Tables) Tables http://middlefieldbank.bank/20231231/role/statement-note-7-loans-and-related-allowance-for-credit-losses 40 false false R41.htm 995485 - Disclosure - Note 8 - Premises and Equipment (Tables) Sheet http://middlefieldbank.bank/20231231/role/statement-note-8-premises-and-equipment-tables Note 8 - Premises and Equipment (Tables) Tables http://middlefieldbank.bank/20231231/role/statement-note-8-premises-and-equipment 41 false false R42.htm 995486 - Disclosure - Note 9 - Goodwill and Intangible Assets (Tables) Sheet http://middlefieldbank.bank/20231231/role/statement-note-9-goodwill-and-intangible-assets-tables Note 9 - Goodwill and Intangible Assets (Tables) Tables http://middlefieldbank.bank/20231231/role/statement-note-9-goodwill-and-intangible-assets 42 false false R43.htm 995487 - 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Disclosure - Note 4 - Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) by Component, Net of Tax (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-4-accumulated-other-comprehensive-income-loss-changes-in-accumulated-other-comprehensive-income-loss-by-component-net-of-tax-details Note 4 - Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) by Component, Net of Tax (Details) Details http://middlefieldbank.bank/20231231/role/statement-note-4-accumulated-other-comprehensive-income-loss-tables 62 false false R63.htm 995507 - Disclosure - Note 5 - Fair Value Measurements (Details Textual) Sheet http://middlefieldbank.bank/20231231/role/statement-note-5-fair-value-measurements-details-textual Note 5 - Fair Value Measurements (Details Textual) Details http://middlefieldbank.bank/20231231/role/statement-note-5-fair-value-measurements-tables 63 false false R64.htm 995508 - Disclosure - Note 5 - Fair Value Measurements - Assets Measured on a Recurring Basis (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-5-fair-value-measurements-assets-measured-on-a-recurring-basis-details Note 5 - Fair Value Measurements - Assets Measured on a Recurring Basis (Details) Details 64 false false R65.htm 995509 - Disclosure - Note 5 - Fair Value Measurements - Fair Value Reconciliation of Level 3 Assets (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-5-fair-value-measurements-fair-value-reconciliation-of-level-3-assets-details Note 5 - Fair Value Measurements - Fair Value Reconciliation of Level 3 Assets (Details) Details 65 false false R66.htm 995510 - Disclosure - Note 5 - Fair Value Measurements - Assets Measured on a Nonrecurring Basis (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-5-fair-value-measurements-assets-measured-on-a-nonrecurring-basis-details Note 5 - Fair Value Measurements - Assets Measured on a Nonrecurring Basis (Details) Details 66 false false R67.htm 995511 - 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Investments and Equity Securities (Details Textual) Details http://middlefieldbank.bank/20231231/role/statement-note-6-investments-and-equity-securities-tables 69 false false R70.htm 995514 - Disclosure - Note 6 - Investments and Equity Securities - Amortized Cost and Fair Values of Securities Available for Sale (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-6-investments-and-equity-securities-amortized-cost-and-fair-values-of-securities-available-for-sale-details Note 6 - Investments and Equity Securities - Amortized Cost and Fair Values of Securities Available for Sale (Details) Details 70 false false R71.htm 995515 - Disclosure - Note 6 - Investments and Equity Securities - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-6-investments-and-equity-securities-amortized-cost-and-fair-value-of-debt-securities-by-contractual-maturity-details Note 6 - Investments and Equity Securities - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Details) Details 71 false false R72.htm 995516 - Disclosure - Note 6 - Investments and Equity Securities - Gross Unrealized Losses and Fair Value (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-6-investments-and-equity-securities-gross-unrealized-losses-and-fair-value-details Note 6 - Investments and Equity Securities - Gross Unrealized Losses and Fair Value (Details) Details 72 false false R73.htm 995517 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses (Details Textual) Sheet http://middlefieldbank.bank/20231231/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/20231231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-tables 73 false false R74.htm 995518 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Primary Segments of the Loan Portfolio (Details) Sheet http://middlefieldbank.bank/20231231/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 74 false false R75.htm 995519 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Allowance for Loan Losses (Details) Sheet http://middlefieldbank.bank/20231231/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 75 false false R76.htm 995520 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Classes of the Loan Portfolio Summarized by Credit Quality (Details) Sheet http://middlefieldbank.bank/20231231/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 76 false false R77.htm 995521 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Collateral-dependent Loans (Details) Sheet http://middlefieldbank.bank/20231231/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 77 false false R78.htm 995522 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Past Due Loans (Details) Sheet http://middlefieldbank.bank/20231231/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 78 false false R79.htm 995523 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Nonaccrual Loans (Details) Sheet http://middlefieldbank.bank/20231231/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 79 false false R80.htm 995524 - Disclosure - Note 7 - Loans and Related Allowance for Credit Losses - Troubled Debt Restructurings (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-7-loans-and-related-allowance-for-credit-losses-troubled-debt-restructurings-details Note 7 - Loans and Related Allowance for Credit Losses - Troubled Debt Restructurings (Details) Details 80 false false R81.htm 995525 - Disclosure - Note 7 - Loans and Related Allowance for Loan and Lease Losses - Impaired Loans by Class (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-7-loans-and-related-allowance-for-loan-and-lease-losses-impaired-loans-by-class-details Note 7 - Loans and Related Allowance for Loan and Lease Losses - Impaired Loans by Class (Details) Details 81 false false R82.htm 995526 - Disclosure - Note 7 - Loans and Related Allowance for Loan and Lease Losses - Additional Information on Impaired Loans (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-7-loans-and-related-allowance-for-loan-and-lease-losses-additional-information-on-impaired-loans-details Note 7 - 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Short-term Borrowings - Outstanding Balances and Related Information of Short-term Borrowings (Details) Details 94 false false R95.htm 995539 - Disclosure - Note 13 - Other Borrowings (Details Textual) Sheet http://middlefieldbank.bank/20231231/role/statement-note-13-other-borrowings-details-textual Note 13 - Other Borrowings (Details Textual) Details http://middlefieldbank.bank/20231231/role/statement-note-13-other-borrowings-tables 95 false false R96.htm 995540 - Disclosure - Note 13 - Other Borrowings - Other Borrowings (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-13-other-borrowings-other-borrowings-details Note 13 - Other Borrowings - Other Borrowings (Details) Details 96 false false R97.htm 995541 - Disclosure - Note 13 - Other Borrowings - Maturities of Other Borrowings (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-13-other-borrowings-maturities-of-other-borrowings-details Note 13 - Other Borrowings - Maturities of Other Borrowings (Details) Details 97 false false R98.htm 995542 - Disclosure - Note 14 - Accrued Interest Payable and Other Liabilities - Components of Accrued Interest Payable and Other Liabilities (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-14-accrued-interest-payable-and-other-liabilities-components-of-accrued-interest-payable-and-other-liabilities-details Note 14 - Accrued Interest Payable and Other Liabilities - Components of Accrued Interest Payable and Other Liabilities (Details) Details 98 false false R99.htm 995543 - Disclosure - Note 15 - Income Taxes (Details Textual) Sheet http://middlefieldbank.bank/20231231/role/statement-note-15-income-taxes-details-textual Note 15 - Income Taxes (Details Textual) Details http://middlefieldbank.bank/20231231/role/statement-note-15-income-taxes-tables 99 false false R100.htm 995544 - Disclosure - Note 15 - Income Taxes - The Provision (Benefit) for Federal Income Taxes (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-15-income-taxes-the-provision-benefit-for-federal-income-taxes-details Note 15 - 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Disclosure - Note 16 - Employee Benefits - Activity Related to Restricted Stock Units Awarded (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-16-employee-benefits-activity-related-to-restricted-stock-units-awarded-details Note 16 - Employee Benefits - Activity Related to Restricted Stock Units Awarded (Details) Details 104 false false R105.htm 995549 - Disclosure - Note 17 - Commitments and Contingent Liabilities (Details Textual) Sheet http://middlefieldbank.bank/20231231/role/statement-note-17-commitments-and-contingent-liabilities-details-textual Note 17 - Commitments and Contingent Liabilities (Details Textual) Details http://middlefieldbank.bank/20231231/role/statement-note-17-commitments-and-contingent-liabilities-tables 105 false false R106.htm 995550 - Disclosure - Note 17 - Commitments and Contingent Liabilities - Outstanding Commitments and Contingent Liabilities (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-17-commitments-and-contingent-liabilities-outstanding-commitments-and-contingent-liabilities-details Note 17 - 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Maturities of Lease Liabilities (Details) Sheet http://middlefieldbank.bank/20231231/role/statement-note-17-commitments-and-contingent-liabilities-maturities-of-lease-liabilities-details Note 17 - Commitments and Contingent Liabilities - Maturities of Lease Liabilities (Details) Details 109 false false R110.htm 995554 - Disclosure - Note 18 - Regulatory Restrictions (Details Textual) Sheet http://middlefieldbank.bank/20231231/role/statement-note-18-regulatory-restrictions-details-textual Note 18 - Regulatory Restrictions (Details Textual) Details http://middlefieldbank.bank/20231231/role/statement-note-18-regulatory-restrictions 110 false false R111.htm 995555 - Disclosure - Note 19 - Regulatory Capital (Details Textual) Sheet http://middlefieldbank.bank/20231231/role/statement-note-19-regulatory-capital-details-textual Note 19 - Regulatory Capital (Details Textual) Details http://middlefieldbank.bank/20231231/role/statement-note-19-regulatory-capital-tables 111 false false R112.htm 995556 - 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