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Note 6 - Fair Value Measurements - Change in Fair Value Measurement Impacts Net Income (Details) - Valuation, Market Approach [Member] - Weighted Average [Member]	Sep. 30, 2022
Pull-through Rate [Member] | Interest Rate Contract [Member]
Derivative asset (liability)	0.4697
Pull-through Rate [Member] | Forward Contract [Member]
Derivative asset (liability)	0.4697
Current Reference Price [Member] | Interest Rate Contract [Member]
Derivative asset (liability)	0.9483
Current Reference Price [Member] | Forward Contract [Member]
Derivative asset (liability)	0.9483

X

- Definition

Value of input used to measure net derivative asset (liability).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

+ Details

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

X

- Details

Name:	us-gaap_ValuationTechniqueAxis=us-gaap_MarketApproachValuationTechniqueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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

X

- Details

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

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=nksh_ForwardContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MeasurementInputTypeAxis=nksh_CurrentReferencePriceMember
Namespace Prefix:
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Balance Type:
Period Type: