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v2.4.1.9

Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Loans by Credit Quality Indicator (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
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Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | $ 608,018 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment | $ 591,198 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Construction, 1-4 Family Residential [Member] | Real Estate Construction [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 15,382 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_Construction14FamilyResidentialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 14,222 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_Construction14FamilyResidentialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Construction, 1-4 Family Residential [Member] | Real Estate Construction [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 2,193 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_Construction14FamilyResidentialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 2,265 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_Construction14FamilyResidentialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Construction Other [Member] | Real Estate Construction [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 24,072 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ConstructionOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 29,047 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ConstructionOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Construction Other [Member] | Real Estate Construction [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans |  | 28 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ConstructionOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Equity Lines [Member] | Consumer Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 15,765 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_EquityLinesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 15,861 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_EquityLinesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Equity Lines [Member] | Consumer Real Estate [Member] | Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 60 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_EquityLinesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 59 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_EquityLinesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Equity Lines [Member] | Consumer Real Estate [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 62 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_EquityLinesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 60 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_EquityLinesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Closed-end First Liens [Member] | Consumer Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 78,600 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 78,806 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Closed-end First Liens [Member] | Consumer Real Estate [Member] | Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 919 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 1,566 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Closed-end First Liens [Member] | Consumer Real Estate [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 1,355 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 1,412 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Closed-end Junior Liens [Member] | Consumer Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 4,397 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 4,258 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Closed-end Junior Liens [Member] | Consumer Real Estate [Member] | Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 26 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 21 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Closed-end Junior Liens [Member] | Consumer Real Estate [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 64 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 95 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Investor-owned Residential Real Estate [Member] | Consumer Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 42,140 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 42,781 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Investor-owned Residential Real Estate [Member] | Consumer Real Estate [Member] | Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 693 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 688 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Investor-owned Residential Real Estate [Member] | Consumer Real Estate [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 810 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 614 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Multifamily Real Estate [Member] | Commercial Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 77,083 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 73,611 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Multifamily Real Estate [Member] | Commercial Real Estate [Member] | Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 1,380 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 1,397 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Multifamily Real Estate [Member] | Commercial Real Estate [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 844 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 850 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 128,861 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 125,643 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member] | Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 61 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 202 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 3,303 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 2,855 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Commercial Real Estate, Other [Member] | Commercial Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 95,353 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 90,821 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Commercial Real Estate, Other [Member] | Commercial Real Estate [Member] | Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 936 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 1,177 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Commercial Real Estate, Other [Member] | Commercial Real Estate [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 504 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 582 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Commercial and Industrial [Member] | Commercial Non Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 29,689 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 31,247 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Commercial and Industrial [Member] | Commercial Non Real Estate [Member] | Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 101 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 97 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Commercial and Industrial [Member] | Commercial Non Real Estate [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 1,720 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 1,390 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
States & Political Subdivisions [Member] | Public Sector and IDA [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 53,441 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_StatesPoliticalSubdivisionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_PublicSectorAndIdaMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 41,361 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_StatesPoliticalSubdivisionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_PublicSectorAndIdaMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Credit Card Receivable [Member] | Consumer Non Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 5,500 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CreditCardReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 5,705 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CreditCardReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Automobile [Member] | Consumer Non Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 11,505 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 11,505 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Automobile [Member] | Consumer Non Real Estate [Member] | Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 95 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 93 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Automobile [Member] | Consumer Non Real Estate [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 114 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 128 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Other Consumer Loans [Member] | Consumer Non Real Estate [Member] | Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 10,977 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_OtherConsumerLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 10,745 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_OtherConsumerLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Other Consumer Loans [Member] | Consumer Non Real Estate [Member] | Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 8 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_OtherConsumerLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |
Other Consumer Loans [Member] | Consumer Non Real Estate [Member] | Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 5 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_OtherConsumerLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | 6 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_OtherConsumerLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember
Real Estate Construction [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 41,647 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember | 45,562 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember
Consumer Real Estate [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 144,891 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | 146,221 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember
Commercial Real Estate [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 308,325 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | 297,138 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember
Commercial Non Real Estate [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 31,510 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | 32,734 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember
Public Sector and IDA [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 53,441 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_PublicSectorAndIdaMember | 41,361 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_PublicSectorAndIdaMember
Consumer Non Real Estate [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 28,204 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | 28,182 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember
Pass [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 592,765 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 575,613 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Special Mention [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | 4,279 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 5,300 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Classified Excluding Impaired [Member] |  |
Financing Receivable, Recorded Investment [Line Items] |  |
Non-impaired gross loans | $ 10,974 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember | $ 10,285 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_InternalCreditAssessmentAxis = nksh_ClassifiedExcludingImpairedMember

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