Commitments and Contingent Liabilities (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commercial real estate	$ 32,927	$ 23,770
Commercial operating	133,884	139,395
Home equity	23,285	24,071
Other	47,498	52,251
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Asset	237,594	239,487
Number of expected days to fund commitments	ninety days
Financial Standby Letter of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Asset	$ 5,193	$ 4,732
Period when letters of credit expire	one year or less

- Definition

The face amount of Commercial Operating financial assets, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

No definition available.

+ Details

Name:	fmbh_FairValueDisclosureOffBalanceSheetRisksFaceAmountAssetCommercialOperating
Namespace Prefix:	fmbh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The face amount of Commercial Real Estate financial assets, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

No definition available.

+ Details

Name:	fmbh_FairValueDisclosureOffBalanceSheetRisksFaceAmountAssetCommercialRe
Namespace Prefix:	fmbh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The face amount of Home Equity financial assets, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

No definition available.

+ Details

Name:	fmbh_FairValueDisclosureOffBalanceSheetRisksFaceAmountAssetHomeEquity
Namespace Prefix:	fmbh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The face amount of Other financial assets, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

No definition available.

+ Details

Name:	fmbh_FairValueDisclosureOffBalanceSheetRisksFaceAmountAssetOther
Namespace Prefix:	fmbh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of expected days until commitments to originate credit are funded.

+ References

No definition available.

+ Details

Name:	fmbh_NumberOfExpectedDaysToFundCommitments
Namespace Prefix:	fmbh_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period after which standby letters of credit generally expire

+ References

No definition available.

+ Details

Name:	fmbh_PeriodWhenLettersOfCreditExpire
Namespace Prefix:	fmbh_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

The face amount of financial assets, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Details

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

- Details

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