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Earnings per Common Share (Details) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2012 | Sep. 30, 2011 | Sep. 30, 2012 | Sep. 30, 2011
Earnings per Common Share (Textual) [Abstract] |  |  |  |
Average number of common shares outstanding basic and diluted | 4,901,464 | 2,955,649 | 3,623,191 | 2,952,568

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- Details
Name: | fxnc_EarningsPerCommonShareTextualAbstract
Namespace Prefix: | fxnc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS). + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration