XML 117 R103.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Commitments and Contingent Liabilities (Details Textual) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Commitments and Contingent Liabilities (Additional Textual) [Abstract] |  |
Maximum commitment period to make loans | 30 days |
Standby letters of credit contractual value | $ 4,900,000 | $ 4,300,000
Maximum subscription amount committed in SBIC investment funds | 8,000,000 |
Investment in SBIC funds | $ 5,000,000 |
Fixed Rate |  |
Commitments and Contingent Liabilities (Textual) [Abstract] |  |
Fixed rate loan commitments maturity range |  | 15 years
Commitments and Unused Lines of Credit | Minimum |  |
Commitments and Contingent Liabilities (Textual) [Abstract] |  |
Debt Instrument, Interest Rate, Stated Percentage | 2.99% | 0.10%
Commitments and Unused Lines of Credit | Maximum |  |
Commitments and Contingent Liabilities (Textual) [Abstract] |  |
Debt Instrument, Interest Rate, Stated Percentage | 16.00% | 18.00%
Commitments to make loans | Minimum |  |
Commitments and Contingent Liabilities (Textual) [Abstract] |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 4.25%
Debt Instrument, Variable Interest Rate Percentage |  | 4.69%
Commitments to make loans | Maximum |  |
Commitments and Contingent Liabilities (Textual) [Abstract] |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 5.25%
Debt Instrument, Variable Interest Rate Percentage |  | 5.75%

X
- Definition Commitments and Contingent Liabilities (Additional Textual) [Abstract] + References No definition available. + Details
Name: | fmnb_CommitmentsAndContingentLiabilitiesAdditionalTextualAbstract
Namespace Prefix: | fmnb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Commitments and Contingent Liabilities (Textual) [Abstract] + References No definition available. + Details
Name: | fmnb_CommitmentsAndContingentLiabilitiesTextualAbstract
Namespace Prefix: | fmnb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Debt instrument variable interest rate. + References No definition available. + Details
Name: | fmnb_DebtInstrumentVariableInterestRate
Namespace Prefix: | fmnb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Maximum commitment period to make loans. + References No definition available. + Details
Name: | fmnb_MaximumCommitmentPeriodToMakeLoans
Namespace Prefix: | fmnb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum subscription amount committed in SBIC investment funds. + References No definition available. + Details
Name: | fmnb_MaximumSubscriptionAmountCommittedInSBICInvestmentFunds
Namespace Prefix: | fmnb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Standby letters of credit contractual amount. + References No definition available. + Details
Name: | fmnb_StandbyLettersOfCreditContractualAmount
Namespace Prefix: | fmnb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + 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 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentTerm
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The cash outflow associated with the purchase of all investments (debt, security, other) during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585 + Details
Name: | us-gaap_PaymentsToAcquireInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_CreditFacilityAxis=fmnb_FixedRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=fmnb_CommitmentsAndUnusedLinesOfCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_LoanOriginationCommitmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |