Allowance adjustment charge offs.

No definition available.

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Namespace Prefix:	fmnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Financing receivable modification specific reserve to customer.

+ References

No definition available.

+ Details

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Namespace Prefix:	fmnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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- Definition

Troubled debt restructuring commitment to lend additional amount to borrow.

+ References

No definition available.

+ Details

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Namespace Prefix:	fmnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Troubled debt restructurings, modification of loan terms included reduction of stated interest rate, remaining life.

+ References

No definition available.

+ Details

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Namespace Prefix:	fmnb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Troubled debt restructurings payment default.

+ References

No definition available.

+ Details

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Namespace Prefix:	fmnb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	fmnb_TroubledDebtRestructuringTextualAbstract
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Data Type:	xbrli:stringItemType
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- Definition

Amount of allowance for credit losses related to receivables which had been measured under a general allowance for credit losses methodology that are now identified as troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 65

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7484272&loc=SL7484277-172609

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-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

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 34

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953682-111524

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Balance Type:	na
Period Type:	duration

- Definition

For a debtor, the aggregate gain (loss) recognized on the restructuring of payables, after the impact of income tax expense or benefit, arising from the difference between the book value of the debt before the restructuring and the fair value of the payments on the debt after restructuring is complete.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 60

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6402221&loc=d3e15743-112638

+ Details

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Balance Type:	credit
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Troubled Debt Restructurings (Details Textual) (USD $)	3 Months Ended		12 Months Ended
Troubled Debt Restructurings (Details Textual) (USD $)	Mar. 31, 2014	Mar. 31, 2013 Loans	Dec. 31, 2013
Troubled Debt Restructuring (Additional Textual) [Abstract]
Total troubled debt restructurings	$ 8,200,000		$ 8,300,000
Specific reserves to customers	361,000		397,000
Commitments to lend additional amounts to borrowers classified as troubled debt restructurings	0		16,000
Troubled Debt Restructuring (Textual) [Abstract]
Allowance adjustment charge offs	0	16,000
Increase in the allowance for loan losses as a result of the allowance	26,000	3,000
Loans modified as trouble debt restructuring loan		1
Payment default loan period		12 months
Consumer, Indirect
Troubled Debt Restructuring (Textual) [Abstract]
Allowance adjustment charge offs	$ 1,000
Loans modified as trouble debt restructuring loan	2
Payment default loan period	12 months
Minimum
Troubled Debt Restructuring (Textual) [Abstract]
Reduction of the notes stated interest rate	0.865%
Maturity period loans	54 months
Maximum
Troubled Debt Restructuring (Textual) [Abstract]
Reduction of the notes stated interest rate	2.75%
Maturity period loans	120 months