Maximum unrealized loss for available for sale securities.

No definition available.

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

- Definition

Number of securities.

+ References

No definition available.

+ Details

Name:	fmnb_NumberOfSecurities
Namespace Prefix:	fmnb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of securities on unrealized loss position.

+ References

No definition available.

+ Details

Name:	fmnb_NumberOfSecuritiesOnUnrealizedLossPosition
Namespace Prefix:	fmnb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	fmnb_SecuritiesAdditionalTextualAbstract
Namespace Prefix:	fmnb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	fmnb_SecuritiesTextualAbstract
Namespace Prefix:	fmnb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The total amount of proceeds received for the sale of securities, categorized neither as held-to-maturity nor trading securities, during the reporting period.

+ References

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGainsLossesSaleProceeds
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow associated with the sale of securities classified as trading securities and held for investment purposes. Excludes proceeds from trading securities purchased and held principally for the purpose of selling them in the near term (thus held for only a short period of time).

+ References

No definition available.

+ Details

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

Securities (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Securities	Mar. 31, 2013	Dec. 31, 2013 Equity securities
Securities (Additional Textual) [Abstract]
Proceeds from the sale	$ 9
Proceeds from sale of investment securities		32
Gross gains realized		14
Number of securities	419
Number of securities with unrealized loss position	118
Securities (Textual) [Abstract]
Unrealized losses for Mortgage-backed securities residential			$ 1