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v2.4.1.9

Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Troubled Debt Restructurings (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Financing Receivable, Modifications [Line Items] |  |  |  |
Number of contracts | 5 us-gaap_FinancingReceivableModificationsNumberOfContracts2 |  | 6 us-gaap_FinancingReceivableModificationsNumberOfContracts2 |
Pre-modification outstanding principal balance | $ 5,761 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 |  | $ 4,401 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 |
Post-modification outstanding principal balance | 5,843 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 | [1] | 4,576 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 | [1]
Closed-end First Liens [Member] | Consumer Real Estate [Member] |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Number of contracts | 1 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember |  | 2 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember |
Pre-modification outstanding principal balance | 126 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember |  | 453 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember |
Post-modification outstanding principal balance | 143 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] | 525 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1]
Multifamily Real Estate [Member] | Commercial Real Estate [Member] |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Number of contracts | 1 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |  |  |
Pre-modification outstanding principal balance | 2,484 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |  |  |
Post-modification outstanding principal balance | 2,484 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |  |
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member] |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Number of contracts | 1 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |  | 1 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |
Pre-modification outstanding principal balance | 184 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |  | 154 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |
Post-modification outstanding principal balance | 208 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] | 239 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1]
Commercial Real Estate, Non Owner Occupied [Member] | Commercial Real Estate [Member] |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Number of contracts | 2 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateNonOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |  | 1 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateNonOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |
Pre-modification outstanding principal balance | 2,967 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateNonOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |  | 3,500 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateNonOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |
Post-modification outstanding principal balance | 3,008 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateNonOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] | 3,500 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateNonOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1]
Closed-end Junior Liens [Member] | Consumer Real Estate [Member] |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Number of contracts |  |  | 1 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember |
Pre-modification outstanding principal balance |  |  | 262 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember |
Post-modification outstanding principal balance |  |  | 267 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1]
Commercial and Industrial [Member] | Commercial Non Real Estate [Member] |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Number of contracts |  |  | 1 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember |
Pre-modification outstanding principal balance |  |  | 32 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember |
Post-modification outstanding principal balance |  |  | $ 45 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1]
Consumer Real Estate [Member] |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Number of contracts |  |  | 2 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember |
Commercial Real Estate [Member] |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |
Number of contracts |  |  | 1 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember |
[1] | Post-modification outstanding recorded investment considers amounts immediately following the modification. Amounts do not reflect balances at the end of the period.

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