Debt instrument interest rate reduction percentage.

No definition available.

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- Definition

Debt instrument maturity date length of extension period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
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- Definition

Financing receivable period of modified contractually past due loans to be considered as payment default.

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

Provision (reversal) for loan losses expensed.

+ References

No definition available.

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

+ Details

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Balance Type:	credit
Period Type:	instant

- 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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Period Type:	duration

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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=66008989&loc=SL6953682-111524

+ Details

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Period Type:	duration

- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reflects the unfunded portion of contractual agreements to lend funds to borrowers for loans whose terms have been modified by troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18794-111554

+ Details

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

- Details

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- Details

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- Details

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- Details

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Data Type:	na
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- Details

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Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ContractualInterestRateReductionMember
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Data Type:	na
Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Troubled Debt Restructurings (Details Textual)	3 Months Ended		6 Months Ended		12 Months Ended
Troubled Debt Restructurings (Details Textual)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($) Loans	Jun. 30, 2016 USD ($) Loans	Jun. 30, 2015 USD ($) Loans	Dec. 31, 2015 USD ($)
Financing Receivable Modifications [Line Items]
Total troubled debt restructurings	$ 7,800,000		$ 7,800,000		$ 9,300,000
Specific reserves to customers	151,000		151,000		497,000
Commitments to lend additional amounts to borrowers classified as troubled debt restructurings	0		0		0
Provision for loan losses	990,000	$ 850,000	$ 1,770,000	$ 1,300,000
Residential real estate, Home equity lines of credit
Financing Receivable Modifications [Line Items]
Troubled debt restructured loans with subsequent payment defaults \| Loans \| Loans			1
Residential real estate loan and home equity line of credit
Financing Receivable Modifications [Line Items]
Loans default payment past due period			30 days
Commercial real estate
Financing Receivable Modifications [Line Items]
Provision for loan losses					0
Troubled debt restructured loans with subsequent payment defaults \| Loans \| Loans		1	2	1
Residential real estate indirect
Financing Receivable Modifications [Line Items]
Troubled debt restructured loans with subsequent payment defaults \| Loans \| Loans			1
Troubled debt restructurings
Financing Receivable Modifications [Line Items]
Specific reserves to customers	154,000		$ 154,000		$ 528,000
Allowance adjustment charge offs	316,000	$ 87,000	327,000	$ 87,000
Provision for loan losses	$ 0	$ 62,000	$ 11,000	$ 62,000
Contractual Interest Rate Reduction
Financing Receivable Modifications [Line Items]
Reduction of the notes stated interest rate	1.24%		1.24%
Extended Maturity
Financing Receivable Modifications [Line Items]
Maturity period loans			120 months	9 months
Troubled debt restructurings subsequent \| Residential real estate loan and home equity line of credit
Financing Receivable Modifications [Line Items]
Provision for loan losses			$ 0