Stock Incentive Plan Summary of Unvested Options (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, Nonvested, Number		0fmbh_OptionsNonvestedNumber	6,625fmbh_OptionsNonvestedNumber	20,875fmbh_OptionsNonvestedNumber
Options, Nonvested, Weighted Average Grant Date Fair Value		$ 0.00	$ 2.51	$ 3.16
Options, Vested in Period, Number		(6,375)fmbh_OptionsVestedInPeriodNumber	(14,250)fmbh_OptionsVestedInPeriodNumber
Options, Vested in Period, Weighted Average Grant Date Fair Value		$ 3.47	$ 3.47
Options, Vested In Period, Fair Value	$ 0fmbh_OptionsVestedInPeriodFairValue	$ 17,000fmbh_OptionsVestedInPeriodFairValue	$ 49,000fmbh_OptionsVestedInPeriodFairValue
Options, Forfeited In Period, Number		(250)
Options, Forfeited in Period, Weighted Average Grant Date Fair Value		$ 3.68

Number of shares subject to options forfeited In period

No definition available.

Name:	fmbh_Fmbh_OptionsForfeitedInPeriodNumber
Namespace Prefix:	fmbh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Options, Forfeited in Period, Weighted Average Grant Date Fair Value

No definition available.

Name:	fmbh_OptionsForfeitedinPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	fmbh_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

The number of non-vested stock options that validly exist and are outstanding as of the balance sheet date.

No definition available.

Name:	fmbh_OptionsNonvestedNumber
Namespace Prefix:	fmbh_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

The weighted average fair value of nonvested stock options that validly exist and are outstanding as of the balance sheet date.

No definition available.

Name:	fmbh_OptionsNonvestedWeightedAverageGrantDateFairValue
Namespace Prefix:	fmbh_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

The fair value of shares subject to options that vested during the year

No definition available.

Name:	fmbh_OptionsVestedInPeriodFairValue
Namespace Prefix:	fmbh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The number of stock options that vested during the reporting period.

No definition available.

Name:	fmbh_OptionsVestedInPeriodNumber
Namespace Prefix:	fmbh_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Weighted Average Grant Date Fair Value of stock options that vested during the period.

No definition available.

Name:	fmbh_OptionsVestedInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	fmbh_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

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