Financing receivable acquired loans.

No definition available.

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

- Definition

Financing receivable allowance for credit loss acquired loans collectively evaluated for impairment.

+ References

No definition available.

+ Details

Name:	fmnb_FinancingReceivableAllowanceForCreditLossAcquiredLoansCollectivelyEvaluatedForImpairment
Namespace Prefix:	fmnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Financing receivable allowance for credit loss acquired with deteriorated credit quality.

+ References

No definition available.

+ Details

Name:	fmnb_FinancingReceivableAllowanceForCreditLossAcquiredWithDeterioratedCreditQuality
Namespace Prefix:	fmnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

+ Details

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

- Definition

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

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ 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=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

+ Details

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

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis=us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_UnallocatedFinancingReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans (Details 4) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Ending allowance balance attributable to loans:
Individually evaluated for impairment	$ 92		$ 249
Collectively evaluated for impairment	11,569		10,603
Acquired loans collectively evaluated for impairment	85		0
Total ending allowance balance	11,746	$ 11,319	10,852	$ 9,720	$ 9,390	$ 8,978
Loans:
Loans individually evaluated for impairment	5,697		7,338
Loans collectively evaluated for impairment	1,166,201		1,048,074
Acquired loans	331,560		370,359
Acquired with deteriorated credit quality	833,748		779,340
Loans	1,505,273		1,427,635
Receivables Acquired with Deteriorated Credit Quality
Ending allowance balance attributable to loans:
Acquired with deteriorated credit quality	0		0
Loans:
Acquired with deteriorated credit quality	1,815		1,864
Commercial real estate
Ending allowance balance attributable to loans:
Individually evaluated for impairment	29		86
Collectively evaluated for impairment	3,889		3,491
Acquired loans collectively evaluated for impairment	36		0
Total ending allowance balance	3,954	3,638	3,577	3,210	3,181	3,127
Loans:
Loans individually evaluated for impairment	1,948		3,457
Loans collectively evaluated for impairment	433,957		376,632
Acquired loans	137,534		153,228
Loans	574,408		534,285
Commercial real estate \| Receivables Acquired with Deteriorated Credit Quality
Ending allowance balance attributable to loans:
Acquired with deteriorated credit quality	0		0
Loans:
Acquired with deteriorated credit quality	969		968
Commercial
Ending allowance balance attributable to loans:
Individually evaluated for impairment	4		111
Collectively evaluated for impairment	1,920		1,763
Acquired loans collectively evaluated for impairment	12		0
Total ending allowance balance	1,936	1,846	1,874	1,634	1,452	1,373
Loans:
Loans individually evaluated for impairment	253		477
Loans collectively evaluated for impairment	214,691		195,146
Acquired loans	43,550		48,536
Loans	259,340		245,055
Commercial \| Receivables Acquired with Deteriorated Credit Quality
Ending allowance balance attributable to loans:
Acquired with deteriorated credit quality	0		0
Loans:
Acquired with deteriorated credit quality	846		896
Residential real estate
Ending allowance balance attributable to loans:
Individually evaluated for impairment	59		52
Collectively evaluated for impairment	2,218		2,153
Acquired loans collectively evaluated for impairment	33		0
Total ending allowance balance	2,310	2,321	2,205	2,081	1,914	1,845
Loans:
Loans individually evaluated for impairment	3,388		3,308
Loans collectively evaluated for impairment	309,146		280,215
Acquired loans	132,947		146,672
Loans	445,481		430,195
Residential real estate \| Receivables Acquired with Deteriorated Credit Quality
Ending allowance balance attributable to loans:
Acquired with deteriorated credit quality	0		0
Loans:
Acquired with deteriorated credit quality	0		0
Consumer
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	2,923		2,766
Acquired loans collectively evaluated for impairment	4		0
Total ending allowance balance	2,927	2,813	2,766	2,444	2,218	2,160
Loans:
Loans individually evaluated for impairment	108		96
Loans collectively evaluated for impairment	208,407		196,081
Acquired loans	17,529		21,923
Loans	226,044		218,100
Consumer \| Receivables Acquired with Deteriorated Credit Quality
Ending allowance balance attributable to loans:
Acquired with deteriorated credit quality	0		0
Loans:
Acquired with deteriorated credit quality	0		0
Unallocated
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	619		430
Acquired loans collectively evaluated for impairment	0		0
Total ending allowance balance	619	$ 701	430	$ 351	$ 625	$ 473
Loans:
Loans individually evaluated for impairment	0		0
Loans collectively evaluated for impairment	0		0
Acquired loans	0		0
Loans	0		0
Unallocated \| Receivables Acquired with Deteriorated Credit Quality
Ending allowance balance attributable to loans:
Acquired with deteriorated credit quality	0		0
Loans:
Acquired with deteriorated credit quality	$ 0		$ 0