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v2.4.1.9

Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Dec. 31, 2014
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment | $ 15,192 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment | [1],[2] | $ 13,075 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment | [1],[2] | $ 16,311 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment | [1]
Interest income recognized | 174 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod | [2] | 99 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod | [2] | 473 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod |
Closed-end First Liens [Member] | Consumer Real Estate [Member] |  |  |  |  |  |
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment | 501 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] | 561 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] |  |
Interest income recognized | 7 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] | 4 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] |  |
Closed-end Junior Liens [Member] | Consumer Real Estate [Member] |  |  |  |  |  |
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment | 236 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] | 257 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] |  |
Interest income recognized | 4 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] | 5 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] |  |
Investor-owned Residential Real Estate [Member] | Consumer Real Estate [Member] |  |  |  |  |  |
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment | 76 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] | 79 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1],[2] |  |
Interest income recognized | 1 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] | 1 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [2] |  |
Multifamily Real Estate [Member] | Commercial Real Estate [Member] |  |  |  |  |  |
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment | 2,708 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] | 3,386 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] |  |
Interest income recognized | 25 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2] |  | [2] |  |
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member] |  |  |  |  |  |
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment | 4,974 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] | 5,515 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] |  |
Interest income recognized | 58 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2] | 44 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2] |  |
Commercial Real Estate, Other [Member] | Commercial Real Estate [Member] |  |  |  |  |  |
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment | 6,023 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1],[2] |  |  |  |
Interest income recognized | 80 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [2] |  |  |  |
Commercial and Industrial [Member] | Commercial Non Real Estate [Member] |  |  |  |  |  |
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment | 674 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1],[2] |  |  |  |
Interest income recognized | (1)us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [2] |  |  |  |
Construction Other [Member] | Real Estate Construction [Member] |  |  |  |  |  |
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment |  |  | 3,150 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ConstructionOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember | [1],[2] |  |
Interest income recognized |  |  | 44 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ConstructionOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember | [2] |  |
Commercial [Member] | Commercial Non Real Estate [Member] |  |  |  |  |  |
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment |  |  | 101 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1],[2] |  |
Interest income recognized |  |  | 1 us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [2] |  |
Automobile [Member] | Consumer Non Real Estate [Member] |  |  |  |  |  |
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans, Average Investment and Interest Income Recognized [Line Items] |  |  |  |  |  |
Average recorded investment |  |  | 26 us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1],[2] |  |
Interest income recognized |  |  |  | [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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