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v2.4.1.9

Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans and Associated Reserves (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
--- | --- | ---
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired loans, principal balance | $ 15,434 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance |  | $ 12,985 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance |
Impaired loans, recorded investment | 15,121 us-gaap_ImpairedFinancingReceivableRecordedInvestment | [1] | 12,989 us-gaap_ImpairedFinancingReceivableRecordedInvestment | [1]
Impaired loans, recorded investment for which there is no related allowance | 7,615 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment | [1] | 10,635 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment | [1]
Impaired loans, recorded investment for which there is a related allowance | 7,506 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment | [1] | 2,354 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment | [1]
Impaired loans, related allowance | 282 us-gaap_ImpairedFinancingReceivableRelatedAllowance |  | 624 us-gaap_ImpairedFinancingReceivableRelatedAllowance |
Closed-end First Liens [Member] | Consumer Real Estate [Member] |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired loans, principal balance | 530 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] | 440 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2]
Impaired loans, recorded investment | 503 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] | 442 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2]
Impaired loans, recorded investment for which there is no related allowance | 311 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] | 232 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2]
Impaired loans, recorded investment for which there is a related allowance | 192 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] | 210 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2]
Impaired loans, related allowance | 2 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] | 3 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2]
Closed-end Junior Liens [Member] | Consumer Real Estate [Member] |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired loans, principal balance | 239 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] | 259 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2]
Impaired loans, recorded investment | 239 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] | 261 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2]
Impaired loans, recorded investment for which there is no related allowance |  | [1],[2] |  | [1],[2]
Impaired loans, recorded investment for which there is a related allowance | 239 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] | 261 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2]
Impaired loans, related allowance | 8 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] | 7 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2]
Investor-owned Residential Real Estate [Member] | Consumer Real Estate [Member] |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired loans, principal balance | 77 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] | 81 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2]
Impaired loans, recorded investment | 77 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] | 82 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2]
Impaired loans, recorded investment for which there is no related allowance |  | [1],[2] | 82 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2]
Impaired loans, recorded investment for which there is a related allowance | 77 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] |  | [1],[2]
Impaired loans, related allowance | 4 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] |  | [2]
Multifamily Real Estate [Member] | Commercial Real Estate [Member] |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired loans, principal balance | 2,911 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2] | 3,278 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2]
Impaired loans, recorded investment | 2,735 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] | 3,274 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2]
Impaired loans, recorded investment for which there is no related allowance | 868 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] | 3,274 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2]
Impaired loans, recorded investment for which there is a related allowance | 1,866 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] |  | [1],[2]
Impaired loans, related allowance | 170 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2] |  | [2]
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member] |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired loans, principal balance | 4,919 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2] | 5,643 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2]
Impaired loans, recorded investment | 4,821 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] | 5,645 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2]
Impaired loans, recorded investment for which there is no related allowance | 3,314 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] | 3,864 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2]
Impaired loans, recorded investment for which there is a related allowance | 1,508 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] | 1,781 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2]
Impaired loans, related allowance | 74 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2] | 610 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2]
Commercial Real Estate, Other [Member] | Commercial Real Estate [Member] |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired loans, principal balance | 6,080 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2] | 3,158 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2]
Impaired loans, recorded investment | 6,068 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] | 3,158 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2]
Impaired loans, recorded investment for which there is no related allowance | 3,072 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] | 3,158 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2]
Impaired loans, recorded investment for which there is a related allowance | 2,996 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] |  | [1],[2]
Impaired loans, related allowance | 14 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2] |  | [2]
Commercial and Industrial [Member] | Commercial Non Real Estate [Member] |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired loans, principal balance | 678 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [2] | 102 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [2]
Impaired loans, recorded investment | 678 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1],[2] | 103 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1],[2]
Impaired loans, recorded investment for which there is no related allowance | 50 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1],[2] | 1 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1],[2]
Impaired loans, recorded investment for which there is a related allowance | 628 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1],[2] | 102 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1],[2]
Impaired loans, related allowance | 10 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [2] | 4 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [2]
Automobile [Member] | Consumer Non Real Estate [Member] |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired loans, principal balance |  |  | 24 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [2]
Impaired loans, recorded investment |  |  | 24 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1],[2]
Impaired loans, recorded investment for which there is no related allowance |  |  | 24 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1],[2]
Impaired loans, recorded investment for which there is a related allowance |  |  |  | [1],[2]
Impaired loans, related allowance |  |  |  | [2]
[1] | Recorded investment is net of charge-offs and interest paid while a loan is in nonaccrual status.
[2] | Only classes with impaired loans are shown

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- Definition Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 14A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953550-111524 + Details
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- Definition Amount of allowance for credit losses related to recorded investment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524 + Details
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- Definition Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524 + Details
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