XML 69 R54.htm IDEA: XBRL DOCUMENT
v3.22.4

Business Combination & Asset Purchase - Summary of Carrying Amount of Loans (Parenthetical) (Detail) - USD ($) | Dec. 31, 2022 | Dec. 31, 2021 | Oct. 01, 2021 | Apr. 30, 2021
--- | --- | --- | --- | ---
Perpetual Federal Savings Bank [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Fair value adjustment | $ 127,700 | $ 189,800 | $ 237,200 |
Ossian Financial Services, Inc. [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Fair value adjustment | $ 10,100 | $ 320,600 |  | $ 324,800

X
- Definition Certain loans acquired in transfer accounted for as debt securities fair value adjustment. + References No definition available. + Details
Name: | fmao_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesFairValueAdjustment
Namespace Prefix: | fmao_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=fmao_PerpetualFederalSavingBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=fmao_OssianFinancialServiceIncorporatedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |