Note 4 - Allowance for Loan Losses - Allowance by Impairment Methodology and Loans by Impairment Methodology (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Beginning balance	$ 4,934	$ 5,009	$ 5,009
Charge-offs	(504)	(447)	(884)
Recoveries	166	233	359
Provision for (recovery of) loan losses	1,700	200	450
Ending balance	6,296	4,995	4,934
Individually evaluated for impairment, allowance	28	101	33
Collectively evaluated for impairment, allowance	6,268	4,894	4,901
Loans	651,516		574,346
Individually evaluated for impairment, loans	5,793	1,775	1,459
Collectively evaluated for impairment, loans	645,723	573,179	572,887
Real Estate 1 [Member] \| Construction and Land Development [Member]
Beginning balance	464	561	561
Charge-offs	0	0	(2)
Recoveries	0	50	50
Provision for (recovery of) loan losses	(68)	(71)	(145)
Ending balance	396	540	464
Individually evaluated for impairment, allowance	0	46	22
Collectively evaluated for impairment, allowance	396	494	442
Loans	31,981		43,164
Individually evaluated for impairment, loans	400	391	367
Collectively evaluated for impairment, loans	31,581	45,890	42,797
Real Estate 1 [Member] \| Secured by Multi-family Residential Properties [Member]
Beginning balance	776	895	895
Charge-offs	0	(58)	(58)
Recoveries	4	5	9
Provision for (recovery of) loan losses	543	(64)	(70)
Ending balance	1,323	778	776
Individually evaluated for impairment, allowance	5	20	11
Collectively evaluated for impairment, allowance	1,318	758	765
Loans	234,188		229,438
Individually evaluated for impairment, loans	497	866	630
Collectively evaluated for impairment, loans	233,691	224,954	228,808
Real Estate 1 [Member] \| Other Real Estate Loans [Member]
Beginning balance	2,296	2,160	2,160
Charge-offs	0	0	(27)
Recoveries	1	0	1
Provision for (recovery of) loan losses	936	233	162
Ending balance	3,233	2,393	2,296
Individually evaluated for impairment, allowance	23	35	0
Collectively evaluated for impairment, allowance	3,210	2,358	2,296
Loans	248,495		236,555
Individually evaluated for impairment, loans	4,896	518	462
Collectively evaluated for impairment, loans	243,599	236,852	236,093
Commercial and Industrial Loans [Member]
Beginning balance	562	464	464
Charge-offs	(69)	(2)	(2)
Recoveries	7	4	8
Provision for (recovery of) loan losses	283	50	92
Ending balance	783	516	562
Individually evaluated for impairment, allowance	0	0	0
Collectively evaluated for impairment, allowance	783	516	562
Loans	124,706		50,153
Individually evaluated for impairment, loans	0	0	0
Collectively evaluated for impairment, loans	124,706	49,353	50,153
Consumer and Other Loans [Member]
Beginning balance	836	929	929
Charge-offs	(435)	(387)	(795)
Recoveries	154	174	291
Provision for (recovery of) loan losses	6	52	411
Ending balance	561	768	836
Individually evaluated for impairment, allowance	0	0	0
Collectively evaluated for impairment, allowance	561	768	836
Loans	12,146		15,036
Individually evaluated for impairment, loans	0	0	0
Collectively evaluated for impairment, loans	$ 12,146	$ 16,130	$ 15,036

Represents the amount of provision (reduction in reserve) for loan losses during the period.

No definition available.

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Namespace Prefix:	fxnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of direct write-downs of accounts receivable charged against the allowance.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

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- Definition

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

+ References

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- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

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- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

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- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=121614798&loc=d3e15032-111544

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

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- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522

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