Stock Incentive Plan Summary of Unvested Options (Details) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, Nonvested, Number	6,625	20,875	35,125	49,375
Options, Nonvested, Weighted Average Grant Date Fair Value	$ 2.51	$ 3.16	$ 3.29	$ 3.34
Options, Vested in Period, Number	(14,250)	(14,250)	(14,250)
Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 3.47	$ 3.47	$ 3.47
Nonvested Awards, Total Compensation Cost Not yet Recognized, Stock Options	$ 0	$ 17,000	$ 69,000

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 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

Aggregate unrecognized cost of option awards made to employees under a stock option plan or plans, that have yet to vest.

No definition available.

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

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