Note 8 - Fair Value (Details Textual)	9 Months Ended
Sep. 30, 2025
Other Real Estate Owned [Member]
Expected Sales Costs to Appraised Value, Percentage	10.00%
Impaired Loans [Member]
Expected Sales Costs to Appraised Value, Percentage	10.00%

Expected sales costs as a percentage of the appraised value.

No definition available.

Name:	fmfg_ExpectedSalesCostsToAppraisedValuePercentage
Namespace Prefix:	fmfg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration