Investment in common equity of Statutory Trust

No definition available.

Name:	fmbh_InvestmentInStatutoryTrust
Namespace Prefix:	fmbh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Trust preferred securities issued and sold through a statutory trust as part of a pooled offering

+ References

No definition available.

+ Details

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Namespace Prefix:	fmbh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=fmbh_FmisTrustIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=fmbh_FmisTrustIiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=fmbh_CLSTrustIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=fmbh_FBTCSTIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_JuniorSubordinatedDebtMember
Namespace Prefix:
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Borrowings Subordinated Debentures (Details) - USD ($)	12 Months Ended
Borrowings Subordinated Debentures (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	May 01, 2018	Sep. 08, 2016	Apr. 26, 2006	Feb. 27, 2004
Debt Instrument [Line Items]
Junior subordinated debentures	$ 18,858,000	$ 29,000,000
FMIS Trust I [Member]
Debt Instrument [Line Items]
Trust preferred securities issued						$ 10,000,000
Investment in Statutory Trust						$ 310,000
FMIS Trust II [Member]
Debt Instrument [Line Items]
Trust preferred securities issued					$ 10,000,000
Investment in Statutory Trust					$ 310,000
Junior subordinated debentures	$ 10,310,000
CLS Trust I [Member]
Debt Instrument [Line Items]
Trust preferred securities issued				$ 4,000,000
Investment in Statutory Trust				$ 124,000
FBTCST I [Member]
Debt Instrument [Line Items]
Trust preferred securities issued			$ 6,000,000
Investment in Statutory Trust			$ 186,000
Junior Subordinated Debt [Member] \| FMIS Trust II [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	bore interest at a fixed rate of 6.98% paid quarterly until June 15, 2011 and then converted to floating rate (LIBOR plus 160 basis points) after June 15, 2011
Debt Instrument, Interest Rate at Period End	3.494%	4.39%
Junior Subordinated Debt [Member] \| CLS Trust I [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	bear interest at three-month LIBOR plus 185 basis points
Debt Instrument, Interest Rate at Period End	3.74%	4.638%
Junior Subordinated Debt [Member] \| FBTCST I [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	bear interest at three-month LIBOR plus 170 basis points
Debt Instrument, Interest Rate at Period End	3.594%	4.488%