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Deposits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2013 | Dec. 31, 2012
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Deposits [Abstract] |  |
Time deposits, in denominations of $100 thousand or more | $ 54.6 | $ 76.6
Brokered deposits | $ 5.1 | $ 8.8

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- Definition Total brokered deposits. + References No definition available. + Details
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Namespace Prefix: | fxnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: | us-gaap_
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- Definition The aggregate amount of domestic and foreign time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $100,000 or more. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 405 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6479006&loc=d3e64164-112818 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Industry Guide -Number 3 -Section V -Paragraph A -Subparagraph 4 + Details
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