Fair Value (Details 4) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Financial assets
Cash and cash equivalents, Carrying Amount	$ 26,929	$ 27,428	$ 29,333	$ 27,513
Restricted stock, Carrying Amount	4,224fmnb_RestrictedStockCarryingValue	4,224fmnb_RestrictedStockCarryingValue
Loans held for sale, Carrying Amount	146us-gaap_LoansReceivableHeldForSaleNet	511us-gaap_LoansReceivableHeldForSaleNet
Loans, net, Carrying Amount	666,061	656,220
Accrued interest receivable, Carrying Amount	3,583us-gaap_InterestReceivable	3,237us-gaap_InterestReceivable
Financial liabilities
Deposits, Carrying Amount	909,408us-gaap_Deposits	915,703us-gaap_Deposits
Short-term borrowings, Carrying Amount	62,218us-gaap_ShortTermBorrowings	59,136us-gaap_ShortTermBorrowings
Long-term borrowings	18,120us-gaap_LongTermDebt	28,381us-gaap_LongTermDebt
Accrued interest payable, Carrying Amount	379	402
Fair Value, Measurements, Recurring
Financial assets
Cash and cash equivalents, Fair Value	26,929	27,428
Loans held for sale, Fair Value	150	523
Loans, net, Fair Value	668,763	658,993
Accrued interest receivable, Fair Value	3,583	3,237
Financial liabilities
Deposits, Fair Value	909,391	915,460
Short-term borrowings, Fair Value	62,218	59,136
Long-term borrowings, Fair Value	18,612	28,837
Accrued interest payable, Fair value	379	402
Fair Value, Measurements, Recurring \| Level 1
Financial assets
Cash and cash equivalents, Fair Value	11,800	11,410
Loans held for sale, Fair Value	0	0
Loans, net, Fair Value	0	0
Accrued interest receivable, Fair Value	0	0
Financial liabilities
Deposits, Fair Value	712,362	708,752
Short-term borrowings, Fair Value	0	0
Long-term borrowings, Fair Value	0	0
Accrued interest payable, Fair value	2	2
Fair Value, Measurements, Recurring \| Level 2
Financial assets
Cash and cash equivalents, Fair Value	15,129	16,018
Loans held for sale, Fair Value	150	523
Loans, net, Fair Value	0	0
Accrued interest receivable, Fair Value	1,822	1,645
Financial liabilities
Deposits, Fair Value	197,029	206,708
Short-term borrowings, Fair Value	62,218	59,136
Long-term borrowings, Fair Value	18,612	28,837
Accrued interest payable, Fair value	377	400
Fair Value, Measurements, Recurring \| Level 3
Financial assets
Cash and cash equivalents, Fair Value	0	0
Loans held for sale, Fair Value	0	0
Loans, net, Fair Value	668,763	658,993
Accrued interest receivable, Fair Value	1,761	1,592
Financial liabilities
Deposits, Fair Value	0	0
Short-term borrowings, Fair Value	0	0
Long-term borrowings, Fair Value	0	0
Accrued interest payable, Fair value	$ 0	$ 0

Accrued interest payable fair value.

No definition available.

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- Definition

Accrued interest receivable fair value.

+ References

No definition available.

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- Definition

Cash cash equivalents and federal funds sold fair value.

+ References

No definition available.

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- Definition

Restricted stock carrying value.

+ References

No definition available.

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- Definition

The sum of cash and cash equivalents plus Federal Funds Sold. Cash and cash equivalents consist of short term, highly liquid investments that are readily convertible to known amounts of cash and are so near their maturity that they present negligible risk of changes in value due to changes in interest rates -- usually with an original maturity less than 90 days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.1,2,3)

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- Definition

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

+ References

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- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

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- Definition

Amount of interest payable on debt, including, but not limited to, trade payables.

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-Topic 942

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-Paragraph 1

-Subparagraph (SX 210.9-03.15(5))

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-Number 210

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-Subparagraph 5

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- Definition

Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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-Publisher FASB

-Name Accounting Standards Codification

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- Definition

Amount after allowance and 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 and loans held for sale.

+ References

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- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Glossary Loan

-URI http://asc.fasb.org/extlink&oid=6517073

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- Definition

Amount classified as loans attributable to disposal group held for sale or disposed of. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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+ Details

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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-Number 210

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-Paragraph 13

-Subparagraph 2, 3

-Article 9

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

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