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v3.23.1

Loans - Schedule of Collateral-dependent Loans (Detail) $ in Thousands | Mar. 31, 2023 USD ($)
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Financing Receivable, Credit Quality Indicator [Line Items] |
Collateral dependent loans | $ 9
Commercial and Industrial [Member] |
Financing Receivable, Credit Quality Indicator [Line Items] |
Collateral dependent loans | $ 9

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- Definition Financial collateral dependent loans. + References No definition available. + Details
Name: | fmao_FinancialCollateralDependentLoans
Namespace Prefix: | fmao_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |