XML 39 R35.htm IDEA: XBRL DOCUMENT v2.4.1.9
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Impaired Loans and Associated Reserves (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Financing Receivable, Impaired [Line Items]      
Total loans, principal balance $ 15,375us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance [1] $ 15,434us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance [1]  
Total loans, recorded investment 14,994us-gaap_ImpairedFinancingReceivableRecordedInvestment [1],[2] 15,121us-gaap_ImpairedFinancingReceivableRecordedInvestment [1],[2] 12,602us-gaap_ImpairedFinancingReceivableRecordedInvestment
Total loans, recorded investment for which there is no related allowance 11,265us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment [1],[2] 7,615us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment [1],[2] 10,139us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
Total loans, recorded investment for which there is a related allowance 3,729us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment [1],[2] 7,506us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment [1],[2] 2,463us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Total loans, related allowance 236us-gaap_ImpairedFinancingReceivableRelatedAllowance [1] 282us-gaap_ImpairedFinancingReceivableRelatedAllowance [1] 280us-gaap_ImpairedFinancingReceivableRelatedAllowance
Closed-end First Liens [Member] | Consumer Real Estate [Member]      
Financing Receivable, Impaired [Line Items]      
Total loans, principal balance 526us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1] 530us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1]  
Total loans, recorded investment 499us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2] 503us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2]  
Total loans, recorded investment for which there is no related allowance 309us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2] 311us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2]  
Total loans, recorded investment for which there is a related allowance 190us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2] 192us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2]  
Total loans, related allowance 2us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1] 2us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1]  
Closed-end Junior Liens [Member] | Consumer Real Estate [Member]      
Financing Receivable, Impaired [Line Items]      
Total loans, principal balance 234us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1] 239us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1]  
Total loans, recorded investment 234us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2] 239us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2]  
Total loans, recorded investment for which there is no related allowance    [1],[2]    [1],[2]  
Total loans, recorded investment for which there is a related allowance 234us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2] 239us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2]  
Total loans, related allowance 8us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1] 8us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1]  
Investor-owned Residential Real Estate [Member] | Consumer Real Estate [Member]      
Financing Receivable, Impaired [Line Items]      
Total loans, principal balance 76us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1] 77us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1]  
Total loans, recorded investment 76us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2] 77us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2]  
Total loans, recorded investment for which there is no related allowance 76us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2]    [1],[2]  
Total loans, recorded investment for which there is a related allowance    [1],[2] 77us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1],[2]  
Total loans, related allowance    [1] 4us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 [1]  
Multifamily Real Estate [Member] | Commercial Real Estate [Member]      
Financing Receivable, Impaired [Line Items]      
Total loans, principal balance 2,907us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1] 2,911us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1]  
Total loans, recorded investment 2,705us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2] 2,735us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2]  
Total loans, recorded investment for which there is no related allowance 868us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2] 868us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2]  
Total loans, recorded investment for which there is a related allowance 1,837us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2] 1,866us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2]  
Total loans, related allowance 148us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1] 170us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1]  
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member]      
Financing Receivable, Impaired [Line Items]      
Total loans, principal balance 4,902us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1] 4,919us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1]  
Total loans, recorded investment 4,799us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2] 4,821us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2]  
Total loans, recorded investment for which there is no related allowance 3,404us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2] 3,314us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2]  
Total loans, recorded investment for which there is a related allowance 1,395us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2] 1,508us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2]  
Total loans, related allowance 68us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1] 74us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1]  
Commercial Real Estate, Other [Member] | Commercial Real Estate [Member]      
Financing Receivable, Impaired [Line Items]      
Total loans, principal balance 6,058us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1] 6,080us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1]  
Total loans, recorded investment 6,009us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2] 6,068us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2]  
Total loans, recorded investment for which there is no related allowance 6,009us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2] 3,072us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2]  
Total loans, recorded investment for which there is a related allowance    [1],[2] 2,996us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1],[2]  
Total loans, related allowance    [1] 14us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 [1]  
Commercial and Industrial [Member] | Commercial Non Real Estate [Member]      
Financing Receivable, Impaired [Line Items]      
Total loans, principal balance 672us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 [1] 678us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 [1]  
Total loans, recorded investment 672us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 [1],[2] 678us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 [1],[2]  
Total loans, recorded investment for which there is no related allowance 599us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 [1],[2] 50us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 [1],[2]  
Total loans, recorded investment for which there is a related allowance 73us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 [1],[2] 628us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 [1],[2]  
Total loans, related allowance $ 10us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 [1] $ 10us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 [1]  
[1] Only classes with impaired loans are shown
[2] Recorded investment is net of charge-offs and interest paid while a loan is in nonaccrual status.