Note 7 - Capital Requirements (Details Textual)	3 Months Ended	6 Months Ended	12 Months Ended
Mar. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Capital Conservation Buffer Phase, Period	4 years
Capital Conservation Buffer Percentage, Annual Installment	0.625%
Capital Conservation Buffer, Percentage	2.50%		1.875%
Capital Conservation Buffer Percentage, Maintained at Bank		6.24%	5.62%

Represents the amount of capital conservation buffer, as a percentage, required to be contributed per year over the capital conservation phase-in period.

No definition available.

Name:	fxnc_CapitalConservationBufferPercentageAnnualInstallment
Namespace Prefix:	fxnc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration