Note 14 - Fair Value (Details Textual)	12 Months Ended
Dec. 31, 2019
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:	num:percentItemType
Balance Type:	na
Period Type:	duration