XML 62 R50.htm IDEA: XBRL DOCUMENT v3.8.0.1

Capital Requirements - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018	Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2017	Jan. 01, 2017	Jan. 01, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer period	4 years
Capital conservation buffer percentage	1.875%		0.625%	1.25%	0.625%	0.625%
Capital conservation buffer percentage maintained at bank	5.52%			5.12%
Scenario, Forecast
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer percentage		0.625%

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

- 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:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: