Financing receivable acquired loans.

No definition available.

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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

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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

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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

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 4
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-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

+ Details

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522

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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

Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-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=120391452&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522

+ Details

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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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Period Type:

- Details

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- Details

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Loans (Details 4) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Ending allowance balance attributable to loans:
Individually evaluated for impairment	$ 436	$ 61
Collectively evaluated for impairment	21,526	14,320
Acquired loans collectively evaluated for impairment	182	106
Total ending allowance balance	22,144	14,487	$ 13,592	$ 12,315
Loans:
Loans individually evaluated for impairment	6,613	4,253
Loans collectively evaluated for impairment	1,800,444	1,614,267
Acquired loans	270,070	192,329
Acquired with deteriorated credit quality	1,345,862	1,097,240
Loans	2,078,044	1,811,539
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	917	690
Commercial real estate
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	10,400	5,790
Acquired loans collectively evaluated for impairment	97	53
Total ending allowance balance	10,497	5,843	5,036	4,260
Loans:
Loans individually evaluated for impairment	502	561
Loans collectively evaluated for impairment	758,050	702,226
Acquired loans	135,884	86,431
Loans	894,950	789,413
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	514	195
Commercial
Ending allowance balance attributable to loans:
Individually evaluated for impairment	357	2
Collectively evaluated for impairment	4,546	2,309
Acquired loans collectively evaluated for impairment	17	12
Total ending allowance balance	4,920	2,323	2,093	2,011
Loans:
Loans individually evaluated for impairment	3,086	205
Loans collectively evaluated for impairment	424,379	290,017
Acquired loans	23,044	17,110
Loans	450,912	307,827
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	403	495
Residential real estate
Ending allowance balance attributable to loans:
Individually evaluated for impairment	79	59
Collectively evaluated for impairment	3,392	2,777
Acquired loans collectively evaluated for impairment	65	39
Total ending allowance balance	3,536	2,875	2,837	2,521
Loans:
Loans individually evaluated for impairment	2,836	3,240
Loans collectively evaluated for impairment	414,568	413,446
Acquired loans	105,936	82,615
Loans	523,340	499,301
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	2,520	2,708
Acquired loans collectively evaluated for impairment	3	2
Total ending allowance balance	2,523	2,710	2,963	2,848
Loans:
Loans individually evaluated for impairment	189	247
Loans collectively evaluated for impairment	203,447	208,578
Acquired loans	5,206	6,173
Loans	208,842	214,998
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	668	736
Acquired loans collectively evaluated for impairment	0	0
Total ending allowance balance	668	736	$ 663	$ 675
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