Name:	nksh_FinancingReceivableNumberOfOtherModifications
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Data Type:	xbrli:integerItemType
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The additional number of other modifications on financing receivable during period.

No definition available.

Name:	nksh_FinancingReceivableNumberOfOtherModificationsAddition
Namespace Prefix:	nksh_
Data Type:	xbrli:integerItemType
Balance Type:	na
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Number of principal and interest payment deferrals on loans receivable related to loan modification programs offered to financial institution customers affected by COVID-19

No definition available.

Name:	nksh_FinancingReceivableNumberOfPrincipalAndInterestPaymentDeferrals
Namespace Prefix:	nksh_
Data Type:	xbrli:integerItemType
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The additional number of principal and interest payment deferrals during period.

No definition available.

Name:	nksh_FinancingReceivableNumberOfPrincipalAndInterestPaymentDeferralsAddition
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Data Type:	xbrli:integerItemType
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The additional amount of financing receivable received other modifications during period.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Deferred amounts of principal and interest payments on loans receivable related to loan modification programs offered to financial institution customers affected by COVID-19.

No definition available.

Name:	nksh_FinancingReceivablePrincipalAndInterestDeferredPayments
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

The additional amount of principal and interest deferred payments on loans receivable during period.

No definition available.

Name:	nksh_FinancingReceivablePrincipalAndInterestDeferredPaymentsAddition
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
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Increase in the percentage of allocation for loans rated classified.

No definition available.

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Data Type:	num:percentItemType
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Increase in the percentage of allocation for loans rated special mention.

No definition available.

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Data Type:	num:percentItemType
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Represents the threshold period for considering loans as special mention or classified.

No definition available.

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Amount of financing receivable modified as troubled debt restructuring.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554

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Data Type:	xbrli:monetaryItemType
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Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953682-111524

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The aggregate interest and fee income generated by: (1) loans the Entity has positive intent and ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (a) industrial and agricultural; (b) real estate; and (c) real estate construction loans; (d) trade financing; (e) lease financing; (f) home equity lines-of-credit; (g) automobile and other vehicle loans; and (h) credit card and other revolving-type loans and (2) loans and leases held-for-sale which may include mortgage loans, direct financing, and sales-type leases.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.1)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

Name:	us-gaap_InternalCreditAssessmentAxis=nksh_ClassifiedExcludingImpairedMember
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