Name:	fmfg_BankingRegulationCommonEquityTierOneRiskbasedCapitalCapitalAdequacyMinimumIncludingConversionBuffer
Namespace Prefix:	fmfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Ratio of minimum Common Equity Tier 1 risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework, including conversion buffer.

No definition available.

Name:	fmfg_BankingRegulationCommonEquityTierOneRiskbasedCapitalRatioCapitalAdequacyMinimumIncludingConversionBuffer
Namespace Prefix:	fmfg_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Amount of minimum Tier 1 leverage capital required for capital adequacy as defined by regulatory framework, including conversion buffer.

No definition available.

Name:	fmfg_BankingRegulationTierOneLeverageCapitalCapitalAdequacyMinimumIncludingConversionBuffer
Namespace Prefix:	fmfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Ratio of minimum Tier 1 leverage capital to average assets required for capital adequacy as defined by regulatory framework, including conversion buffer.

No definition available.

Name:	fmfg_BankingRegulationTierOneLeverageCapitalRatioCapitalAdequacyMinimumIncludingConversionBuffer
Namespace Prefix:	fmfg_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Amount of minimum Tier 1 risk-based capital required for capital adequacy as defined by regulatory framework, including conversion buffer.

No definition available.

Name:	fmfg_BankingRegulationTierOneRiskbasedCapitalCapitalAdequacyMinimumIncludingConversionBuffer
Namespace Prefix:	fmfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Ratio of minimum Tier 1 risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework, including conversion buffer.

No definition available.

Name:	fmfg_BankingRegulationTierOneRiskbasedCapitalRatioCapitalAdequacyMinimumIncludingConversionBuffer
Namespace Prefix:	fmfg_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Amount of minimum total risk-based capital required for capital adequacy as defined by regulatory framework, including capital conversion buffer.

No definition available.

Name:	fmfg_BankingRegulationTotalRiskbasedCapitalCapitalAdequacyMinimumIncludingCapitalConservationBuffer
Namespace Prefix:	fmfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Ratio of minimum total risk-based capital to risk-weighted assets required for capital adequacy as defined by regulatory framework, including conversion buffer.

No definition available.

Name:	fmfg_BankingRegulationTotalRiskbasedCapitalRatioCapitalAdequacyMinimumIncludingConversionBuffer
Namespace Prefix:	fmfg_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Ratio of minimum Common Equity Tier 1 risk-based capital to risk-weighted assets categorized as well capitalized as defined by regulatory framework for prompt corrective action.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1

Name:	us-gaap_BankingRegulationCommonEquityTierOneRiskBasedCapitalRatioWellCapitalizedMinimum
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Amount of minimum total risk-based capital categorized as well capitalized as defined by regulatory framework for prompt corrective action.

Name:	us-gaap_CapitalRequiredToBeWellCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Ratio of minimum total risk-based capital to risk-weighted assets categorized as well capitalized as defined by regulatory framework for prompt corrective action.

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Ratio of total risk-based capital to risk-weighted assets as defined by regulatory framework.

Name:	us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Value of capital units or capital shares. This element is relevant to issuers of face-amount certificates and registered investment companies.

No definition available.

Name:	us-gaap_CapitalUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of Common Equity Tier 1 risk-based capital as defined by regulatory framework.

Name:	us-gaap_CommonEquityTierOneCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Ratio of Common Equity Tier 1 risk-based capital to risk-weighted assets as defined by regulatory framework.

Name:	us-gaap_CommonEquityTierOneCapitalRatio
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Amount of minimum Common Equity Tier 1 risk-based capital categorized as well capitalized as defined by regulatory framework for prompt corrective action.

Name:	us-gaap_CommonEquityTierOneCapitalRequiredToBeWellCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of Tier 1 leverage capital as defined by regulatory framework.

Name:	us-gaap_TierOneLeverageCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of minimum Tier 1 leverage capital categorized as well capitalized as defined by regulatory framework for prompt corrective action.

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Ratio of minimum Tier 1 leverage capital to average assets categorized as well capitalized as defined by regulatory framework for prompt corrective action.

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Ratio of Tier 1 capital to average assets as defined by regulatory framework.

Name:	us-gaap_TierOneLeverageCapitalToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Amount of Tier 1 risk-based capital as defined by regulatory framework.

Name:	us-gaap_TierOneRiskBasedCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of minimum Tier 1 risk-based capital categorized as well capitalized as defined by regulatory framework for prompt corrective action.

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Ratio of minimum Tier 1 risk-based capital to risk-weighted assets categorized as well capitalized as defined by regulatory framework for prompt corrective action.

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Ratio of Tier 1 risk-based capital to risk-weighted assets as defined by regulatory framework.