XML 40 R29.htm IDEA: XBRL DOCUMENT
v3.20.2

Business Combination and Asset Purchase - Summary of Carrying Amount of Loans (Parenthetical) (Detail) - USD ($) | Sep. 30, 2020 | Dec. 31, 2019 | Jan. 01, 2019
--- | --- | --- | ---
Business Combinations [Abstract] |  |  |
Fair value adjustment | $ 0 | $ 62,000 | $ 2,118,000

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
- References No definition available. + Details
Name: | us-gaap_BusinessCombinationsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration