XML 96 R64.htm IDEA: XBRL DOCUMENT v2.4.1.9

Loans - Loans Individually Evaluated for Impairment by Portfolio Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 301fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember	$ 300fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember
Unpaid Principal Balance	326fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember	300fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember
Related Allowance	36fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember	78fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember
Average Recorded Investment	170fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember	342fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember
Interest Income Recognized	7fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember	15fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember
Interest Income Recognized Cash Basis	7fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember	13fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember
Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		88fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember
Unpaid Principal Balance		88fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember
Related Allowance		9fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember
Average Recorded Investment	108fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember	72fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember
Interest Income Recognized	7fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember
Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	25fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgriculturalLoanMember
Unpaid Principal Balance	25fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgriculturalLoanMember
Related Allowance	25fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgriculturalLoanMember
Average Recorded Investment	2fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = fmb_AgriculturalLoanMember
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,180fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember	1,675fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember
Unpaid Principal Balance	1,180fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember	2,022fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember
Related Allowance	111fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember	295fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember
Average Recorded Investment	823fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember	1,148fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember
Interest Income Recognized	28fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember	43fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember
Interest Income Recognized Cash Basis	26fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember	3fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	326fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember	377fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember
Unpaid Principal Balance	326fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember	377fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember
Related Allowance	204fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember	134fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember
Average Recorded Investment	825fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember	1,752fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember
Interest Income Recognized	45fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember	2fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember
Interest Income Recognized Cash Basis	18fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember	1fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	11fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ConsumerLoanMember
Unpaid Principal Balance	11fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ConsumerLoanMember
Related Allowance	11fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ConsumerLoanMember
Average Recorded Investment	1fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_ConsumerLoanMember
With No Related Allowance Recorded [Member] | Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	204fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	18fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Unpaid Principal Balance	229fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	18fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Average Recorded Investment	52fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	138fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Interest Income Recognized	1fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	10fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Interest Income Recognized Cash Basis	1fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	10fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
With No Related Allowance Recorded [Member] | Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	93fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Interest Income Recognized	7fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
With No Related Allowance Recorded [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	471fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	906fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Unpaid Principal Balance	471fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	906fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Average Recorded Investment	740fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	630fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Interest Income Recognized	7fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	21fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Interest Income Recognized Cash Basis	5fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	3fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
With No Related Allowance Recorded [Member] | Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	319fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember	203fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Interest Income Recognized	45fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
Interest Income Recognized Cash Basis	18fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithNoRelatedAllowanceRecordedMember
With a Specific Allowance Recorded [Member] | Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	97fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	282fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Unpaid Principal Balance	97fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	282fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Related Allowance	36fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	78fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Average Recorded Investment	118fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	204fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Interest Income Recognized	6fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	5fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Interest Income Recognized Cash Basis	6fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	3fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_ResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
With a Specific Allowance Recorded [Member] | Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		88fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Unpaid Principal Balance		88fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Related Allowance		9fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Average Recorded Investment	15fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	72fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = fmb_AgricultureRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
With a Specific Allowance Recorded [Member] | Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	25fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgriculturalLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Unpaid Principal Balance	25fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgriculturalLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Related Allowance	25fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = fmb_AgriculturalLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Average Recorded Investment	2fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = fmb_AgriculturalLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
With a Specific Allowance Recorded [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	709fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	769fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Unpaid Principal Balance	709fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	1,116fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Related Allowance	111fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	295fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Average Recorded Investment	83fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	518fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Interest Income Recognized	21fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	22fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Interest Income Recognized Cash Basis	21fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
With a Specific Allowance Recorded [Member] | Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	326fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	377fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Unpaid Principal Balance	326fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	377fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Related Allowance	204fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	134fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Average Recorded Investment	506fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember	1,549fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Interest Income Recognized		2fmb_ImpairedFinancingReceivablesInterestIncomeRecognized / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Interest Income Recognized Cash Basis		1fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis / us-gaap_FinancialInstrumentAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
With a Specific Allowance Recorded [Member] | Consumer [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	11fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Unpaid Principal Balance	11fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Related Allowance	11fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod / us-gaap_FinancialInstrumentAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember
Average Recorded Investment	$ 1fmb_FinancingReceivableAverageRecordedInvestment / us-gaap_FinancialInstrumentAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fmb_WithSpecificAllowanceRecordedMember

X

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

No definition available.

+ Details

Name:	fmb_FinancingReceivableAverageRecordedInvestment
Namespace Prefix:	fmb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Impaired financing receivable recorded investment during period.

+ References

No definition available.

+ Details

Name:	fmb_ImpairedFinancingReceivableRecordedInvestmentDuringPeriod
Namespace Prefix:	fmb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Impaired financing receivable related allowance during period.

+ References

No definition available.

+ Details

Name:	fmb_ImpairedFinancingReceivableRelatedAllowanceDuringPeriod
Namespace Prefix:	fmb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Impaired financing receivables interest income recognized.

+ References

No definition available.

+ Details

Name:	fmb_ImpairedFinancingReceivablesInterestIncomeRecognized
Namespace Prefix:	fmb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Impaired Financing Receivables Interest Income Recognized Cash Basis

+ References

No definition available.

+ Details

Name:	fmb_ImpairedFinancingReceivablesInterestIncomeRecognizedCashBasis
Namespace Prefix:	fmb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Impaired financing receivable unpaid principal balance during period.

+ References

No definition available.

+ Details

Name:	fmb_ImpairedFinancingReceivableUnpaidPrincipalBalanceDuringPeriod
Namespace Prefix:	fmb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	us-gaap_FinancingReceivableImpairedLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=fmb_AgriculturalLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=fmb_AgricultureRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fmb_WithNoRelatedAllowanceRecordedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fmb_WithSpecificAllowanceRecordedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: