XML 66 R54.htm IDEA: XBRL DOCUMENT
v3.19.1

Capital Requirements - Narrative (Detail) | 3 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Mar. 31, 2019 | Jan. 01, 2019 | Dec. 31, 2018 | Jan. 01, 2018 | Jan. 01, 2017 | Jan. 01, 2016
Regulatory Capital Requirements [Abstract] |  |  |  |  |  |
Capital conservation buffer period | 4 years |  |  |  |  |
Capital conservation buffer percentage | 2.50% | 0.625% | 1.875% | 0.625% | 0.625% | 0.625%
Capital conservation buffer percentage maintained at bank | 6.49% |  | 5.62% |  |  |

X
- Definition Capital conservation buffer percentage. + References No definition available. + Details
Name: | fxnc_CapitalConservationBufferPercentage
Namespace Prefix: | fxnc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Capital conservation buffer percentage maintained at bank. + References No definition available. + Details
Name: | fxnc_CapitalConservationBufferPercentageMaintainedAtBank
Namespace Prefix: | fxnc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Capital conservation buffer phase period. + References No definition available. + Details
Name: | fxnc_CapitalConservationBufferPhasePeriod
Namespace Prefix: | fxnc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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