Allowance for Loan Losses (Details Textual) (USD $)	3 Months Ended
Mar. 31, 2013 Contract	Mar. 31, 2012 Contract	Dec. 31, 2012
Allowance for Loan Losses (Textual) [Abstract]
Troubled debt restructurings (TDRs)	$ 6,500,000		$ 6,300,000
TDRs performing under the restructured terms	4,100,000		1,600,000
New loans modified under TDRs	0	0
Troubled debt restructuring loan subsequent default	$ 0	$ 0

Name:	fxnc_AllowanceForLoanLossesTextualAbstract
Namespace Prefix:	fxnc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Financing receivable subsequent default recorded investment.

+ References

No definition available.

+ Details

Name:	fxnc_FinancingReceivableSubsequentDefaultRecordedInvestment
Namespace Prefix:	fxnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Performing troubled debt restructurings.

+ References

No definition available.

+ Details

Name:	fxnc_PerformingTroubledDebtRestructurings
Namespace Prefix:	fxnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=7512638&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of investment in financing receivables (before modification) modified by troubled debt restructurings.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant