Note 3 - Loans and Allowance for Credit Losses - Loans and Allowance for Loan Losses by Evaluation Method (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Allowance for loan losses	$ 10,502	$ 9,094	$ 10,626	$ 8,225
Loans, individually evaluated	13,471	10,544
Loans, collectively evaluated	976,427	846,631
Loans	989,898	857,175
Individually Evaluated [Member]
Allowance for loan losses	644	572
Collectively Evaluated [Member]
Allowance for loan losses	9,858	8,522
Real Estate Construction Portfolio Segment[Member]
Allowance for loan losses	549	408	476	450
Loans, individually evaluated	276	286
Loans, collectively evaluated	81,079	55,093
Loans	81,355	55,379
Real Estate Construction Portfolio Segment[Member] \| Individually Evaluated [Member]
Allowance for loan losses	0	0
Real Estate Construction Portfolio Segment[Member] \| Collectively Evaluated [Member]
Allowance for loan losses	549	408
Consumer Real Estate Portfolio Segment [Member]
Allowance for loan losses	3,635	3,162	3,365	2,199
Loans, individually evaluated	2,259	1,183
Loans, collectively evaluated	297,051	240,381
Loans	299,310	241,564
Consumer Real Estate Portfolio Segment [Member] \| Individually Evaluated [Member]
Allowance for loan losses	114	74
Consumer Real Estate Portfolio Segment [Member] \| Collectively Evaluated [Member]
Allowance for loan losses	3,521	3,088
Commercial Real Estate Portfolio Segment [Member]
Allowance for loan losses	4,254	3,576	4,341	3,642
Loans, individually evaluated	10,452	8,805
Loans, collectively evaluated	444,526	410,325
Loans	454,978	419,130
Commercial Real Estate Portfolio Segment [Member] \| Individually Evaluated [Member]
Allowance for loan losses	391	367
Commercial Real Estate Portfolio Segment [Member] \| Collectively Evaluated [Member]
Allowance for loan losses	3,863	3,209
Commercial Non Real Estate Segment [Member]
Allowance for loan losses	748	682	1,216	930
Loans, individually evaluated	305	227
Loans, collectively evaluated	51,992	41,328
Loans	52,297	41,555
Commercial Non Real Estate Segment [Member] \| Individually Evaluated [Member]
Allowance for loan losses	117	126
Commercial Non Real Estate Segment [Member] \| Collectively Evaluated [Member]
Allowance for loan losses	631	556
Public Sector and IDA Portfolio Segment[Member]
Allowance for loan losses	323	333	301	319
Loans, individually evaluated	0	0
Loans, collectively evaluated	59,043	60,551
Loans	59,043	60,551
Public Sector and IDA Portfolio Segment[Member] \| Individually Evaluated [Member]
Allowance for loan losses	0	0
Public Sector and IDA Portfolio Segment[Member] \| Collectively Evaluated [Member]
Allowance for loan losses	323	333
Consumer Non Real Estate Portfolio Segment [Member]
Allowance for loan losses	593	583	593	506
Loans, individually evaluated	179	43
Loans, collectively evaluated	42,736	38,953
Loans	42,915	38,996
Consumer Non Real Estate Portfolio Segment [Member] \| Individually Evaluated [Member]
Allowance for loan losses	22	5
Consumer Non Real Estate Portfolio Segment [Member] \| Collectively Evaluated [Member]
Allowance for loan losses	571	578
Unallocated Financing Receivables [Member]
Allowance for loan losses	400	350	$ 334	$ 179
Unallocated Financing Receivables [Member] \| Individually Evaluated [Member]
Allowance for loan losses	0	0
Unallocated Financing Receivables [Member] \| Collectively Evaluated [Member]
Allowance for loan losses	$ 400	$ 350

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-11B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph c
-Publisher SEC

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (1)
-Publisher SEC

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (3)
-Publisher SEC

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(4))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amortized cost, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

+ Details

Name:	us-gaap_FinancingReceivableBeforeAllowanceForCreditLossAndFee
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of financing receivable collectively evaluated for credit loss. Excludes financing receivable individually evaluated for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.5.a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480418/310-10-S99-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-11C

+ Details

Name:	us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of financing receivable individually evaluated for credit loss. Excludes financing receivable collectively evaluated for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.5.a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480418/310-10-S99-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-11C

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_ClassOfFinancingReceivableTypeOfBorrowerAxis=nksh_IndividuallyEvaluatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ClassOfFinancingReceivableTypeOfBorrowerAxis=nksh_CollectivelyEvaluatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=nksh_RealEstateConstructionPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=nksh_ConsumerRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=nksh_CommercialNonRealEstateSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=nksh_PublicSectorAndIDAPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=nksh_ConsumerNonRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_UnallocatedFinancingReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: