The percentage the employer matches of the employee's percentage contribution between two and six percent.

No definition available.

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

- Definition

The period of time over which the employer's matching contributions vest under the benefit plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	fxnc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum age an employee must be in order to participate in the benefit plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	fxnc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of fixed, monthly payments under the retirement benefit plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	fxnc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of hours of service required by eligible employees in order to receive additional contributions from the employer under the benefit plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	fxnc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents state percentage of employees contribution for defined contribution plan.

+ References

No definition available.

+ Details

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

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of employees eligible to participate in defined contribution plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Note 10 - Benefit Plans (Details Textual) $ in Thousands		6 Months Ended
Note 10 - Benefit Plans (Details Textual) $ in Thousands	Mar. 15, 2019	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)
Defined Contribution Plan, Employer Matching Contribution, Percent of Match		1.00%
Defined Contribution Plan, Employer Matching Contribution for Employee's Contribution Between Two and Six Percent, Percent of Match		50.00%
Defined Contribution Plan, Service Hours Required by Eligible Employees to Receive Additional Contributions		1,000
Defined Contribution Plan, Minimum Age for Eligibility (Year)		19 years
Defined Contribution Plan, Employer Matching Contribution, Vesting Period (Year)		2 years
Supplemental Employee Retirement Plan [Member]
Defined Contribution Plan, Cost		$ 131	$ 88
Defined Contribution Plan, Number of Employees	3
Defined Contribution Plan, Retirement Benefits Payable, Number of Monthly Payments	180
The 401(k) Plan [Member]
Defined Contribution Plan, Cost		$ 449	$ 436
Minimum [Member]
Defined Contribution Plan, Stated Percentage of Employees Contribution		2.00%
Maximum [Member]
Defined Contribution Plan, Stated Percentage of Employees Contribution		6.00%