XML 88 R72.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Deposits - Additional Information (Detail) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Deposits [Abstract] |  |
Time deposits, in denominations of $250 thousand or more | $ 10,100 | $ 10,600
Brokered deposits | $ 601 | $ 600

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

X
- Definition Time Deposits 250000 Or More + References No definition available. + Details
Name: | fxnc_TimeDeposits250000OrMore
Namespace Prefix: | fxnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_DepositsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration