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v2.4.1.9

Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Past Due and Nonaccrual Loans (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014 | Mar. 31, 2014
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Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | $ 4,105 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue | [1] | $ 2,447 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue | [1] |
90 or more days past due | 3,377 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue | [1] | 2,302 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue | [1] |
90 or more days past due and still accruing | 272 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing | [1] | 207 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing | [1] | 163 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Nonaccrual loans (including impaired nonaccruals) | 9,225 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus | [1] | 9,287 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus | [1] | 6,078 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Construction Other [Member] | Real Estate Construction [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due |  | [1] | 28 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ConstructionOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_RealEstateConstructionMember | [1] |
90 or more days past due |  | [1] |  | [1] |
90 or more days past due and still accruing |  | [1] |  | [1] |
Nonaccrual loans (including impaired nonaccruals) |  | [1] |  | [1] |
Equity Lines [Member] | Consumer Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | 80 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_EquityLinesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] | 25 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_EquityLinesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] |
90 or more days past due |  | [1] |  | [1] |
90 or more days past due and still accruing |  | [1] |  | [1] |
Nonaccrual loans (including impaired nonaccruals) |  | [1] |  | [1] |
Closed-end First Liens [Member] | Consumer Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | 1,117 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] | 719 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] |
90 or more days past due | 131 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] | 185 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] |
90 or more days past due and still accruing | 131 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] | 80 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] |
Nonaccrual loans (including impaired nonaccruals) | 4 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] | 105 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndFirstLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] |
Closed-end Junior Liens [Member] | Consumer Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | 68 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] | 74 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] |
90 or more days past due |  | [1] | 1 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] |
90 or more days past due and still accruing |  | [1] | 1 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_ClosedEndJuniorLiensMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] |
Nonaccrual loans (including impaired nonaccruals) |  | [1] |  | [1] |
Investor-owned Residential Real Estate [Member] | Consumer Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | 378 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] |  |  |
90 or more days past due |  | [1] |  |  |
90 or more days past due and still accruing |  | [1] |  |  |
Nonaccrual loans (including impaired nonaccruals) | 14 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerRealEstateMember | [1] |  |  |
Investor-owned Residential Real Estate [Member] | Commercial Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due |  |  | 336 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
90 or more days past due |  |  | 45 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
90 or more days past due and still accruing |  |  |  | [1] |
Nonaccrual loans (including impaired nonaccruals) |  |  | 59 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_InvestorOwnedResidentialRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
Multifamily Real Estate [Member] | Commercial Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | 844 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] | 850 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
90 or more days past due | 868 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] | 868 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
90 or more days past due and still accruing |  | [1] |  | [1] |
Nonaccrual loans (including impaired nonaccruals) | 2,705 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] | 2,735 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_MultifamilyRealEstateMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | 647 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |  | [1] |
90 or more days past due | 1,588 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] | 1,066 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
90 or more days past due and still accruing |  | [1] | 102 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
Nonaccrual loans (including impaired nonaccruals) | 2,841 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] | 2,573 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOwnerOccupiedMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
Commercial Real Estate, Other [Member] | Commercial Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due |  | [1] |  | [1] |
90 or more days past due |  | [1] | 70 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
90 or more days past due and still accruing |  | [1] |  | [1] |
Nonaccrual loans (including impaired nonaccruals) | 2,959 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] | 3,066 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialRealEstateOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialRealEstateLoansMember | [1] |
Commercial and Industrial [Member] | Commercial Non Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | 777 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1] | 153 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1] |
90 or more days past due | 732 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1] | 43 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1] |
90 or more days past due and still accruing | 83 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1] |  | [1] |
Nonaccrual loans (including impaired nonaccruals) | 702 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1] | 749 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_CommercialNonRealEstateMember | [1] |
Credit Card Receivable [Member] | Consumer Non Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | 3 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CreditCardReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] | 3 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CreditCardReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] |
90 or more days past due | 7 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CreditCardReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] | 4 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CreditCardReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] |
90 or more days past due and still accruing | 7 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CreditCardReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] | 4 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CreditCardReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] |
Nonaccrual loans (including impaired nonaccruals) |  | [1] |  | [1] |
Automobile [Member] | Consumer Non Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | 172 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] | 205 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] |
90 or more days past due | 51 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] | 20 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] |
90 or more days past due and still accruing | 51 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] | 20 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_AutomobileMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] |
Nonaccrual loans (including impaired nonaccruals) |  | [1] |  | [1] |
Other Consumer Loans [Member] | Consumer Non Real Estate [Member] |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |
30 – 89 days past due | 19 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_OtherConsumerLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] | 54 nksh_FinancingReceivableRecordedInvestment30To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = nksh_OtherConsumerLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = nksh_ConsumerNonRealEstateMember | [1] |
90 or more days past due |  | [1] |  | [1] |
90 or more days past due and still accruing |  | [1] |  | [1] |
Nonaccrual loans (including impaired nonaccruals) |  | [1] |  | [1] |
[1] | Only classes with past-due or nonaccrual loans are shown.

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- Definition Financing receivables that are less than 90 days past due but more than 29 days past due. + References No definition available. + Details
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Namespace Prefix: | nksh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Recorded investment in financing receivables that are 90 days or more past due and still accruing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Financing receivables that are equal to or greater than 90 days past due. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953401-111524 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524 + Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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