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Note 3 - Investment Securities Income taxes Note 4 - Loans and Allowance for Credit Losses ecd_NonRule10b51ArrTrmntdFlag Non-Rule 10b5-1 Arrangement Terminated [Flag] Note 5 - Goodwill and Other Intangibles Financial Service, Other [Member] ecd_NonRule10b51ArrAdoptedFlag Non-Rule 10b5-1 Arrangement Adopted [Flag] Note 6 - Capital Standards Trading Arrangements, by Individual [Table] Note 7 - Derivative Financial Instruments Deposit Account [Member] Retirement Benefits [Text Block] Material Terms of Trading Arrangement [Text Block] Note 8 - Fair Value Foreclosure in settlement of loan receivable The foreclosure of loan receivable Note 9 - Earnings per Share Financial Instrument [Axis] Note 11 - Borrowed Funds Investment in Debt and Equity Securities and Other Trading Assets [Text Block] us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss Unrealized losses, held to maturity Note 12 - Stock-based Compensation us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain Unrealized gains, held to maturity Note 3 - Investment Securities - Investments in Debt Securities (Details) us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax Unrealized losses, available for sale Minimum [Member] us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax Unrealized gains, available for sale fmfg_ProvisionForLoanLeaseAndOtherLossesIncludingUnfundedCommitments Provision for (recovery of) credit losses The amount of provision for loan, lease, and other losses, including unfunded commitments. 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Retirement Plan Name [Domain] Note 4 - Loans and Allowance for Credit Losses - Major Categories of Loans (Details) Note 4 - Loans and Allowance for Credit Losses - Past Due Loans (Details) Long-term debt principal payments The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer. Retirement Plan Type [Domain] Note 4 - Loans and Allowance for Credit Losses - Loan Modifications (Details) fmfg_AmortizationOfDebtIssuanceCostsNet Amortization of debt issuance costs The net amount of amortization expense attributable to debt issuance costs. Retirement Plan Name [Axis] Note 4 - Loans and Allowance for Credit Losses - Loans by Credit Grade (Details) fmfg_AccruedInterestReceivableFairValueDisclosure Accrued interest receivable Fair value portion of accrued interest receivable. Retirement Plan Type [Axis] Note 4 - Loans and Allowance for Credit Losses - Allowance for Loan Losses (Details) Note 4 - Loans and Allowance for Credit Losses - Amortizable Yield Premium on Purchased Loans (Details) Note 4 - Loans and Allowance for Credit Losses - Components of Allowance for Credit Losses (Details) Business Description and Basis of Presentation [Text Block] Note 5 - Goodwill and Other Intangibles - Changes in Goodwill and Other Intangibles (Details) Note 6 - Capital Standards - Capital Requirements (Details) Note 7 - Derivative Financial Instruments - Schedule of Derivative Instruments (Details) Note 7 - Derivative Financial Instruments - Derivative Instruments, Gain (Loss) (Details) Note 8 - Fair Value - Summarizes Financial Assets Measured at Fair Value (Details) Secured Debt [Member] Note 8 - Fair Value - Assets Measured on a Nonrecurring Basis (Details) Net unrealized gain (loss) on securities available for sale Note 8 - Fair Value - Estimated Fair Value of Financial Instruments (Details) Note 9 - Earnings per Share - Schedule of Earnings per Share (Details) Note 11 - Borrowed Funds - Borrowed Funds (Details) Note 12 - Stock-based Compensation - Summary of Restricted Stock Unit Activity (Details) Notes To Financial Statements Notes To Financial Statements [Abstract] Salaries us-gaap_DividendsCash Cash dividends, $.36 per share Financial Instruments [Domain] Asset Pledged as Collateral [Member] Securities Sold under Agreements to Repurchase [Member] Weighted Average [Member] us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet Accrued interest receivable Accrued interest payable us-gaap_SharesOutstanding Balance (in shares) Balance (in shares) Decrease (increase) in Deferred loan fees and costs, net us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger 12 months or more Fair value us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months Less than 12 months Fair Value Adjustments to reconcile net income to net cash provided by operating activities Award Type [Axis] us-gaap_Liabilities Total liabilities Banking Regulation, Regulatory Capital Requirement, Compliance [Table] Plan Name [Axis] Defined Benefit Plan [Table] Plan Name [Domain] Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block] us-gaap_LiabilitiesAndStockholdersEquity Total liabilities and stockholders' equity us-gaap_AllocatedShareBasedCompensationExpense Share-Based Payment Arrangement, Expense Pledged Status [Domain] Title and Position [Axis] Credit Rating, Standard & Poor's [Axis] Pledged Status [Axis] Stock based compensation Federal Home Loan Bank of Atlanta [Member] us-gaap_OtherPostretirementBenefitExpense Other Postretirement Benefits Cost (Reversal of Cost) Share-Based Payment Arrangement [Text Block] us-gaap_FiniteLivedIntangibleAssetUsefulLife Finite-Lived Intangible Asset, Useful Life (Year) Portion at Fair Value Measurement [Member] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod Share-Based Compensation Arrangement by Share-Based Payment Award, Shares Issued in Period Reported Value Measurement [Member] Fair Value, by Balance Sheet Grouping [Table] us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect Net (decrease) increase in cash and cash equivalents Furniture and equipment us-gaap_CashAndCashEquivalentsFairValueDisclosure Cash and cash equivalents Estimate of Fair Value Measurement [Member] us-gaap_CommonStockDividendsPerShareCashPaid Common Stock, Dividends, Per Share, Cash Paid (in dollars per share) Accretion Amount of accretion recognized for the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities, with evidence of deterioration of credit quality. 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Common Equity Tier One Capital Required to be Well Capitalized Ratio Banking Regulation, Common Equity Tier 1 Risk-Based Capital Ratio, Well Capitalized, Minimum Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets Share-Based Payment Arrangement, Tranche Two [Member] Tier One Risk Based Capital to Risk Weighted Assets us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss Total Unrealized losses fmfg_PaymentsForProceedsFromLoansMadeToCustomersNetOfPrincipalCollected Loans made to customers, net of principal collected The net amount paid or received by the reporting entity associated with loans made to customers, net of principal collected. us-gaap_LoansReceivableFairValueDisclosure Loans, net us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition Total Fair value fmfg_DebtSecuritiesAvailableforSaleExcludingAccruedInterestNet AFS, net Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), net. 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Financing Receivable Credit Quality Indicators [Table Text Block] Product and Service [Domain] Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease) Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease) Financing Receivable, Modified [Table Text Block] Product and Service [Axis] Federal Home Loan Bank of Atlanta advances fmfg_ProceedsFromPaymentsForFederalHomeLoanBankAdvances Amount of cash flow from proceeds of Federal Home Loan Bank (FHLBank) advances. Ownership [Axis] Ownership [Domain] fmfg_PercentageOfOwnership Percentage of Ownership The percentage of ownership owned by the company. Vested, grant date fair value per share (in dollars per share) Fair value adjustment of equity security Unrealized (gain) loss on equity security First Community Bankers Insurance Co., LLC [Member] First Community Bankers Insurance Co., LLC, a Tennessee “series” limited liability company and licensed property and casualty insurance company. Intercompany balances and transactions have been eliminated. us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Vested, number of shares (in shares) Held-to-Maturity Securities [Member] SBA Pools [Member] SBA pools are securities that are made up of pooled loans from the U. S. Small Business Administration. As a Federal agency, the SBA offers loan guarantees through its 7(a) loan program, which allows small businesses that are unable to otherwise secure financing through normal lending channels to obtain loans. Mortgage loans held for sale Asset Class [Axis] Interest income Loans, including fees Gain (Loss) on Securities [Table Text Block] Assets [Abstract] Measurement Frequency [Axis] Government Deposits and Securities Sold Under Repurchase Agreement [Member] Government Deposits and Securities Sold Under Repurchase Agreement. Statement [Line Items] Construction and Land Development [Member] Represents the information pertaining to construction and land development. Fair Value Hierarchy and NAV [Axis] us-gaap_CommonStockSharesIssued Common Stock, Shares, Issued (in shares) Grantee Status [Domain] Common Stock, Shares, Outstanding (in shares) Award Type [Domain] Share-Based Payment Arrangement, Employee [Member] Common Stock, Shares Authorized (in shares) Grantee Status [Axis] Other real estate owned, net fmfg_OtherRealEstateOwnedFairValueDisclosure Other real estate owned, net Fair value portion of other real estate owned. Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Common stock, par value $.01 per share, authorized 5,000,000 shares; issued and outstanding 3,262,958 shares in 2026 and 3,229,795 shares in 2025 Intangible Asset and Goodwill [Table Text Block] us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo Finite-Lived Intangible Asset, Expected Amortization, Year Two fmfg_InterestBearingDepositsFairValueDisclosure Interest-bearing deposits Fair value portion of interest-bearing deposits. us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree Finite-Lived Intangible Asset, Expected Amortization, Year Three fmfg_NoninterestBearingDepositsFairValueDisclosure Noninterest-bearing deposits Fair value portion of noninterest-bearing deposit liabilities. us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths Intangible Asset, Finite-Lived, Estimated Amortization Expense, Year One us-gaap_InterestPayableCurrentAndNoncurrent Accrued interest payable us-gaap_PolicyTextBlockAbstract Accounting Policies Loans [Member] us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour Finite-Lived Intangible Asset, Expected Amortization, Year Four us-gaap_TableTextBlock Notes Tables us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive Finite-Lived Intangible Asset, Expected Amortization, Year Five Profit Sharing Plan [Member] Represents information pertaining to profit sharing plan. us-gaap_ComprehensiveIncomeNetOfTax Total comprehensive income Amortization (accretion) of right of use asset Amount of periodic reduction over lease term of carrying amount of right-of-use asset from operating lease. us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresMaximumAmountAvailable Federal Home Loan Bank, Advances, General Debt Obligations, Maximum Amount Available Available for sale Held to maturity us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAmountOfAdvancesByBranch Federal Home Loan Bank advances us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate Federal Home Loan Bank advances mature in Federal Home Loan Bank Advances [Member] us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromOneToTwoYearsOfBalanceSheetDate Federal Home Loan Bank, Advance, Maturity, Year Two Restricted stock, at cost Long-term debt, net of issuance costs us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveAmortizedCostBasis Over one to five years Statement of Stockholders' Equity [Abstract] Proceeds from sale of other real estate owned Extended Maturity [Member] Intangible Asset, Finite-Lived, Class [Axis] Statement of Comprehensive Income [Abstract] Loan Restructuring Modification [Axis] Loan Restructuring Modification [Domain] Intangible Asset, Finite-Lived, Class [Domain] us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent Equity security fmfg_IncreaseDecreaseInMortgageLoansHeldforsaleExcludingCollectionOfMortgageLoansHeldforsale Mortgage loans held for sale Represents increase (decrease) in mortgage loans held-for-sale excluding collection of mortgage loans held-for-sale. Statement of Cash Flows [Abstract] Financing Receivable Portfolio Segment [Axis] Other comprehensive loss Stockholders' equity Long-Term Debt, Type [Domain] Equity Components [Axis] Core Deposits [Member] Unfunded Loan Commitment [Member] Dividends reinvested The amount of adjustments related to capital dividends for reinvested adjustment. us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent Total other comprehensive (loss) income Financing Receivable Portfolio Segment [Domain] Equity Component [Domain] Fair Value Measurements, Nonrecurring [Table Text Block] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 [Member] AOCI Attributable to Parent [Member] Fair Value, Inputs, Level 1 [Member] Additional Paid-in Capital [Member] Retained Earnings [Member] Corporate Debt Securities [Member] Subordinated Debt [Member] Premises and equipment, net Financial Asset, Aging [Axis] Loans us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss Loans Deferred income taxes, net Financial Asset, Aging [Domain] fmfg_PurchasedLoansAmortizableYield Beginning balance Ending balance Amount of amortizable yield on purchased loans. Amortizable Yield Premium on Purchased Loans [Table Text Block] Tabular disclosure for amortizable yield premium on purchased loans. us-gaap_ProvisionForLoanLossesExpensed Provision for credit losses us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss Held to maturity securities Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss Financial Asset, 30 to 59 Days Past Due [Member] us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss Amortized cost, available for sale Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss Intangible Asset and Goodwill [Text Block] Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest HTM, allowance for credit losses Beginning balance Beginning balance Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest Loans, allowance for credit losses Allowance for loan losses Allowance for loan losses Financial Asset, 60 to 89 Days Past Due [Member] Financial Asset, Equal to or Greater than 90 Days Past Due [Member] us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAllowanceForCreditLossExcludingAccruedInterest AFS, allowance for credit losses us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear Pass us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear Pass us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear Pass us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear Pass us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear Pass Fair Value Disclosures [Text Block] us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear Pass Fair Value, by Balance Sheet Grouping [Table Text Block] Gain on settlement of fair value hedge Gain on settlement of fair value hedge us-gaap_FinancingReceivableExcludingAccruedInterestRevolving Pass Postage, delivery, and armored carrier Amount of expense associated with postage, delivery and armored carrier. us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments Amortization of premiums and (accretion of discounts), net us-gaap_LongTermDebtFairValue Long-term debt, net us-gaap_MortgagesHeldForSaleFairValueDisclosure Mortgage loans held for sale Collateral Held [Domain] Collateral Held [Axis] Mortgage banking income us-gaap_PaymentsToAcquireHeldToMaturitySecurities Held to maturity Supplemental Employee Retirement Plan [Member] Tier One Risk Based Capital Required to be Well Capitalized Tier One Risk Based Capital Accumulated other comprehensive loss Tier One Leverage Capital Required to be Well Capitalized Tier One Leverage Capital Deferred origination fees net of costs us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest Income before income taxes Additional paid-in capital Debt Disclosure [Text Block] us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1 Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition us-gaap_PaymentsToAcquireProductiveAssets Purchases of premises, equipment and software Stock-based compensation Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Collateral Pledged [Member] Collateralized Mortgage-Backed Securities [Member] us-gaap_NoninterestExpense Total noninterest expense Noninterest expense us-gaap_DebtInstrumentFaceAmount Debt Instrument, Face Amount Financial Asset, Not Past Due [Member] Capital Required to be Well Capitalized Stock-based compensation (in shares) Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Debt Securities, Held-to-Maturity, Credit Quality Indicator [Table Text Block] us-gaap_OffBalanceSheetCreditLossLiability Beginning balance Ending balance Goodwill [Table] Restricted Stock Units (RSUs) [Member] Dividends reinvested (in shares) us-gaap_EmployeeBenefitsAndShareBasedCompensation Employee benefits us-gaap_DebtInstrumentInterestRateStatedPercentage Debt Instrument, Interest Rate, Stated Percentage us-gaap_DebtInstrumentInterestRateDuringPeriod Securites sold under repurchase agreements us-gaap_DerivativeInstrumentsInHedgesLiabilitiesAtFairValue Fair value hedge Schedule of Long-Term Debt Instruments [Table] Reconciliation of net income to net cash provided by operating activities Increase (decrease) in fair value of interest rate swap agreements Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] us-gaap_NetCashProvidedByUsedInOperatingActivities Net cash provided by operating activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] us-gaap_NetCashProvidedByUsedInInvestingActivities Net cash used in investing activities us-gaap_SharesIssuedPricePerShare Shares Issued, Price Per Share us-gaap_NetCashProvidedByUsedInFinancingActivities Net cash provided by financing activities us-gaap_AdvancesFromFederalHomeLoanBanks Federal Home Loan Bank of Atlanta advances us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt Available for sale us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt Proceeds from Sale of Debt Securities, Available-for-Sale Other real estate owned Other real estate owned Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Table Text Block] Advertising Interest-bearing deposits Interest rate contracts designated as hedging instruments Accounting Policies [Abstract] Hedged items US States and Political Subdivisions Debt Securities [Member] Loans, less allowance for credit losses of $4,518 and $4,361 Financing Receivable, Excluding Accrued Interest, after Allowance for Credit Loss Noninterest-bearing deposits fmfg_FiniteLivedIntangibleAssetExpectedAmortizationYearSix Finite-Lived Intangible Asset, Expected Amortization, Year Six Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in the sixth fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). fmfg_FiniteLivedIntangibleAssetExpectedAmortizationYearSeven Finite-Lived Intangible Asset, Expected Amortization, Year Seven Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in the seventh fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Income Statement [Abstract] Provision for (recovery of) credit losses fmfg_IntangibleAssetsNetIncludingGoodwillAmortizationAndImpairment Amortization Amortization amount of intangible assets and impairment amount of goodwill charged during period. Available for sale securities us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest Securities available for sale, at fair value Available for Sale Fair value Total fmfg_FinitelivedIntangibleAssetExpectedAmortizationYearEight Finite-Lived Intangible Asset, Expected Amortization, Year Eight Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in eighth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). fmfg_FiniteLivedIntangibleAssetExpectedAmortizationYearNine Finite-Lived Intangible Asset, Expected Amortization, Year Nine Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in ninth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Securities held to maturity, at amortized cost less allowance for credit losses of $63 and $79 HTM, net fmfg_FinitelivedIntangibleAssetExpectedAmortizationYearTen Finite-Lived Intangible Asset, Expected Amortization, Year Ten Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). us-gaap_ProceedsFromPaymentsForInSecuritiesSoldUnderAgreementsToRepurchase Securities sold under repurchase agreements Net income Net income Net income Financial Asset, Past Due [Member] us-gaap_AmortizationOfIntangibleAssets Amortization, other intangible us-gaap_InterestIncomeExpenseNet Net interest income Unsecured Debt [Member] Capital Required for Capital Adequacy Amount of minimum total risk-based capital required for capital adequacy as defined by regulatory framework, including capital conversion buffer. Tier One Risk Based Capital Required for Capital Adequacy Amount of minimum Tier 1 risk-based capital required for capital adequacy as defined by regulatory framework, including conversion buffer. Common Equity Tier One Capital Required for Capital Adequacy Ratio Ratio of minimum Common Equity Tier 1 risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework, including conversion buffer. Tier One Leverage Capital Required for Capital Adequacy to Average Assets Ratio of minimum Tier 1 leverage capital to average assets required for capital adequacy as defined by regulatory framework, including conversion buffer. Accounting Standards Update and Change in Accounting Principle [Table] Common Equity Tier One Capital Required for Capital Adequacy Amount of minimum Common Equity Tier 1 risk-based capital required for capital adequacy as defined by regulatory framework, including conversion buffer. Tier One Leverage Capital Required for Capital Adequacy Amount of minimum Tier 1 leverage capital required for capital adequacy as defined by regulatory framework, including conversion buffer. Capital Required for Capital Adequacy to Risk Weighted Assets Ratio of minimum total risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework, including conversion buffer. Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Ratio of minimum Tier 1 risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework, including conversion buffer. us-gaap_InterestExpenseLoansFromOtherFederalHomeLoanBanks Federal Home Loan Bank advances Occupancy us-gaap_OtherNoninterestExpense Other Federal Deposit Insurance Corporation premiums Bank owned life insurance income us-gaap_NoninterestIncome Total noninterest income fmfg_OtherRealEstateOwnedNet Other real estate owned expense, net Net amount of expense recognized during the period for the foreclosure on real estate assets. Noninterest income Measurement Basis [Axis] Fair Value Hierarchy and NAV [Domain] Measurement Frequency [Domain] Vesting [Axis] Statement of Financial Position [Abstract] Vesting [Domain] us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestCreditLossExpenseReversal Provision for credit losses us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal Provision for loan losses Cash paid during the period for income taxes us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery Recoveries Other assets us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff Charge-offs Charge-offs Charge-offs Professional services Fair Value, Nonrecurring [Member] Fair Value, Recurring [Member] us-gaap_PaymentsForProceedsFromFederalHomeLoanBankStock Purchase of stock in FHLB of Atlanta Common Equity Tier One Capital us-gaap_IncreaseDecreaseInOtherOperatingAssets Other assets dei_DocumentType Document Type Document Information [Line Items] Document Quarterly Report Document Information [Table] Common Equity Tier One Capital Required to be Well-Capitalized us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateRollingAfter10Years Over ten years us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateRollingAfterOneThroughFiveYears Over one to five years us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment Weighted Average Number of Shares Outstanding, Diluted, Adjustment dei_EntityInteractiveDataCurrent Entity Interactive Data Current us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateRollingAfter5Through10Years Over five to ten years Bank owned life insurance Document Transition Report Certificates of deposit in other banks us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateRollingWithinOneYear Within one year us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding Weighted average shares outstanding (dilutive) (in shares) us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDate Held to Maturity Amortized cost, total Mortgage-backed securities and SBA pools, held to maturity, amortized cost us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis Available for Sale Amortized cost, Fair value, total us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate Available for Sale Fair value, total us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements Effect of dilutive restricted stock units (in shares) us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValue Held to Maturity Fair value, total us-gaap_WeightedAverageNumberOfSharesOutstandingBasic Weighted average shares outstanding (basic) (in shares) Derivative Instrument [Axis] Earnings per common share - basic (in dollars per share) Earnings per share - basic (in dollars per share) Supplemental disclosure of cash flow information: Loans, 90 days past due and still accruing us-gaap_FinancingReceivableExcludingAccruedInterest90DaysOrMorePastDueStillAccruing Earnings Per Share, Basic, by Common Class, Including Two-Class Method [Table] us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage Interest-bearing Title and Position [Domain] us-gaap_Deposits Total deposits Deposits Noninterest-bearing Depreciation and amortization us-gaap_FiniteLivedIntangibleAssetsNet Balance, other intangible Balance, other intangible Document Fiscal Period Focus Pledging Purpose [Axis] Document Fiscal Year Focus Pledging Purpose [Domain] Amendment Flag Common Stock [Member] Federal Home Loan Bank Branch [Domain] Federal Home Loan Bank Branch [Axis] Financing Receivable, Past Due [Table] us-gaap_Goodwill Balance Balance Other liabilities Document Period End Date Residential Portfolio Segment [Member] Legal Entity [Axis] us-gaap_InterestAndDividendIncomeOperating Total interest income Consumer Portfolio Segment [Member] Commercial Real Estate Portfolio Segment [Member] Financing Receivable, Allowance for Credit Loss [Table] Commercial Portfolio Segment [Member] us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment Outstanding loan balances evaluated for impairment individually dei_EntityFileNumber Entity File Number us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment Outstanding loan balances evaluated for impairment collectively Entity Tax Identification Number Supplemental disclosure of non-cash transactions: us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment Allowance for loan losses ending balance evaluated for impairment collectively Unallocated Financing Receivables [Member] us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss Less than 12 months Unrealized losses us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss 12 months or more Unrealized losses Entity [Domain] Entity Central Index Key us-gaap_DebtSecurities Debt Securities dei_EntityRegistrantName Entity Registrant Name Doubtful [Member] us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch Defined Contribution Plan, Employer Matching Contribution, Percent of Match dei_EntityCurrentReportingStatus Entity Current Reporting Status us-gaap_DerivativeGainLossOnDerivativeNet (Gain) on fair value hedge Special Mention [Member] Substandard [Member] Entity Incorporation, State or Country Code Pass [Member] Current Fiscal Year End Date Entity Filer Category dei_EntityShellCompany Entity Shell Company us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesTax Income tax benefit (expense) Entity Emerging Growth Company us-gaap_DerivativeNotionalAmount Derivative, Notional Amount Entity Small Business The 2023 Equity Compensation Plan [Member] Represents the 2023 Equity Compensation Plan. Federal Reserve Bank Advances, Facility One [Member] Borrowings from the Federal Reserve Bank. Hedging Designation [Domain] fmfg_DebtInstrumentsBorrowingCapacityPercentage Debt Instruments, Borrowing Capacity, Percentage Pertains to the approved borrowing capacity in percentage. Hedging asset Derivative Assets Net fair value hedge us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet Financing Receivable, Modified [Table] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Interest expense Write down of other real estate owned Represents the amount of write down on other real estate owned. Federal funds sold and other interest-bearing deposits Pledged Single-family Residential Loans [Member] Pertains to pledging purpose of pledged asset owned. Derivative Instruments and Hedging Activities Disclosure [Text Block] Commercial Banks [Member] Pertains to borrowing arrangements with commercial banks. Pledged Commercial Loan [Member] Pertains to the pledging purpose of pledged asset owned. us-gaap_InterestExpenseDeposits Deposits Entity Address, State or Province Entity Address, City or Town Marketable Securities [Table] Retained earnings us-gaap_InterestExpenseOperating Total interest expense Entity Address, Address Line One Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] City Area Code us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost Over five to ten years Local Phone Number us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost Within one year Entity Address, Postal Zip Code Derivative [Table] Mortgage-backed securities and SBA pools, fair value, available for sale us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue Over five to ten years us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue Over ten years us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue Within one year us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue Over one to five years us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost Over ten years Mortgage-backed securities and SBA pools, amortized cost, available for sale Class of Stock [Axis] us-gaap_InterestExpenseSecuritiesSoldUnderAgreementsToRepurchase Securities sold under repurchase agreements dei_EntityCommonStockSharesOutstanding Entity Common Stock, Shares Outstanding (in shares) Hedging liability us-gaap_DerivativeAssetFairValueGrossLiability Impaired Loans [Member] Represents impaired loans. Earnings Per Share [Text Block] Hedging Designation [Axis] Other Real Estate Owned [Member] Represents the fair value of other real estate owned. Executive Officer [Member] Fair Value Hedging [Member] Financing Receivable, Credit Quality Indicator [Table] Director [Member] Total unrealized (loss) gain on investment securities available for sale Internal Credit Assessment [Axis] Capital Long-term debt Automated teller machine and debit card expenses Amount of expense recognized during the period for automated teller machines and debt card expense. us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss Net interest income after provision for credit losses us-gaap_HeldToMaturitySecuritiesFairValue Fair value, held to maturity Held to Maturity Fair value total fmfg_EquitySecurityDividendsReinvested Equity security dividends reinvested Amount of equity security dividends reinvested. Derivative Instruments, Gain (Loss) [Table Text Block] Investments Classified by Contractual Maturity Date [Table Text Block] Internal Credit Assessment [Domain] us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue Over five to ten years Common Stock, Par or Stated Value Per Share (in dollars per share) us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue Over ten years Investment securities - taxable us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue Within one year us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue Over one to five years us-gaap_OtherLiabilities Other liabilities us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 Allowance for loan losses ending balance evaluated for impairment individually Investment securities - tax exempt Hedging Relationship [Axis] Derivative Contract [Domain] Mortgage-backed securities and SBA pools, held to maturity, fair value Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Cash and due from banks Regulatory Capital Requirements under Banking Regulations [Text Block] fmfg_LongTermDebtMaturitiesRepaymentsOfPrincipalInTenYears Subordinated Debt (net of issuance costs) matures in Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). us-gaap_CashCashEquivalentsAndFederalFundsSold Cash and cash equivalents us-gaap_Assets Total Assets Designated as Hedging Instrument [Member] Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount Defined Contribution Plan, Employer Discretionary Contribution Amount us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent Total Financing Receivables, Percentage us-gaap_FinancingReceivableExcludingAccruedInterestModifiedAccumulated Financing Receivable, Modified us-gaap_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPercentage Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage Earnings per common share - diluted (in dollars per share) Earnings per share - diluted (in dollars per share) Other real estate owned, net Standard & Poor's, AA Rating [Member] External Credit Rating, Standard & Poor's [Domain] Asset Class [Domain] Standard & Poor's, AAA Rating [Member] us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification Financing Receivable, Modified, Weighted-Average Term Increase from Modification (Month) Accounts and Financing Receivables [Table] Standard & Poor's, BBB Rating [Member] Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Standard & Poor's, A Rating [Member] Accrued interest receivable us-gaap_DebtSecuritiesHeldToMaturityAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] Cash paid during the period for interest us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] Interest Rate Swap [Member] Schedule of Long-Term Debt Instruments [Table Text Block] us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff Charge-offs us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff Charge-offs us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff Charge-offs us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff Charge-offs us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Granted us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff Charge-offs us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff Charge-offs us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff Charge-offs us-gaap_SecuritiesSoldUnderAgreementsToRepurchase Securities sold under repurchase agreements Hedging Relationship [Domain] fmfg_ExpectedSalesCostsToAppraisedValuePercentage Expected Sales Costs to Appraised Value, Percentage Expected sales costs as a percentage of the appraised value. us-gaap_StockholdersEquity Total Stockholders' equity Balance Balance us-gaap_DebtSecuritiesHeldToMaturityAccruedInterestAfterAllowanceForCreditLoss Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss Forfeited, grant date fair value per share (in dollars per share) us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss Financing Receivable, Accrued Interest, after Allowance for Credit Loss us-gaap_PaymentsOfDividends Dividends paid, net of reinvestments Consolidation, Less-than-Wholly-Owned Subsidiary, Parent Ownership Interest, Effect of Change [Table] us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLoss Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss Interest Rate Swaption [Member] ecd_Rule10b51ArrTrmntdFlag Rule 10b5-1 Arrangement Terminated [Flag] Other fees and commissions Service charges on deposit accounts ecd_Rule10b51ArrAdoptedFlag Rule 10b5-1 Arrangement Adopted [Flag] fmfg_IncreaseDecreaseInBankOwnedLifeInsuranceCashSurrenderValue Bank owned life insurance cash surrender value The amount of increase (decrease) in bank owned life insurance cash surrender value during the period. Marketable Securities [Table Text Block]