XML 96 R80.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Funds Restrictions and Reserve Balance - Additional Information (Detail) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Aggregate amount of unrestricted funds | $ 1.9 |
First Bank [Member] |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Aggregate amounts of daily average required balances of reserve against its deposits | $ 6.0 | $ 5.6

X
- Definition Aggregate amount of daily average deposit. + References No definition available. + Details
Name: | fxnc_AggregateAmountOfDailyAverageDeposit
Namespace Prefix: | fxnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Aggregate amount of unrestricted funds transferred from bank. + References No definition available. + Details
Name: | fxnc_AggregateAmountOfUnrestrictedFundsTransferredFromBank
Namespace Prefix: | fxnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=fxnc_FirstBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |