XML 68 R38.htm IDEA: XBRL DOCUMENT v2.4.1.9
Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Loans by Credit Quality Indicator (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans $ 608,018us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment $ 591,198us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Construction, 1-4 Family Residential [Member] | Real Estate Construction [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 15,382us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_Construction14FamilyResidentialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_RealEstateConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 14,222us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_Construction14FamilyResidentialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_RealEstateConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Construction, 1-4 Family Residential [Member] | Real Estate Construction [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 2,193us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_Construction14FamilyResidentialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_RealEstateConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 2,265us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_Construction14FamilyResidentialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_RealEstateConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Construction Other [Member] | Real Estate Construction [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 24,072us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ConstructionOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_RealEstateConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 29,047us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ConstructionOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_RealEstateConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Construction Other [Member] | Real Estate Construction [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans   28us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ConstructionOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_RealEstateConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Equity Lines [Member] | Consumer Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 15,765us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_EquityLinesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 15,861us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_EquityLinesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Equity Lines [Member] | Consumer Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 60us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_EquityLinesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 59us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_EquityLinesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Equity Lines [Member] | Consumer Real Estate [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 62us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_EquityLinesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 60us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_EquityLinesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Closed-end First Liens [Member] | Consumer Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 78,600us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 78,806us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Closed-end First Liens [Member] | Consumer Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 919us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 1,566us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Closed-end First Liens [Member] | Consumer Real Estate [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 1,355us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 1,412us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndFirstLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Closed-end Junior Liens [Member] | Consumer Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 4,397us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 4,258us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Closed-end Junior Liens [Member] | Consumer Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 26us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 21us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Closed-end Junior Liens [Member] | Consumer Real Estate [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 64us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 95us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_ClosedEndJuniorLiensMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Investor-owned Residential Real Estate [Member] | Consumer Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 42,140us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 42,781us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Investor-owned Residential Real Estate [Member] | Consumer Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 693us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 688us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Investor-owned Residential Real Estate [Member] | Consumer Real Estate [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 810us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 614us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Multifamily Real Estate [Member] | Commercial Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 77,083us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 73,611us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Multifamily Real Estate [Member] | Commercial Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 1,380us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 1,397us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Multifamily Real Estate [Member] | Commercial Real Estate [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 844us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 850us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 128,861us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 125,643us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 61us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 202us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Commercial Real Estate, Owner Occupied [Member] | Commercial Real Estate [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 3,303us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 2,855us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOwnerOccupiedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Commercial Real Estate, Other [Member] | Commercial Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 95,353us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 90,821us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Commercial Real Estate, Other [Member] | Commercial Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 936us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 1,177us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Commercial Real Estate, Other [Member] | Commercial Real Estate [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 504us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 582us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialRealEstateOtherMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Commercial and Industrial [Member] | Commercial Non Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 29,689us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 31,247us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Commercial and Industrial [Member] | Commercial Non Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 101us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 97us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Commercial and Industrial [Member] | Commercial Non Real Estate [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 1,720us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 1,390us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_CommercialAndIndustrialMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
States & Political Subdivisions [Member] | Public Sector and IDA [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 53,441us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_StatesPoliticalSubdivisionsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_PublicSectorAndIdaMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 41,361us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_StatesPoliticalSubdivisionsMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_PublicSectorAndIdaMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Credit Card Receivable [Member] | Consumer Non Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 5,500us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CreditCardReceivablesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 5,705us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_CreditCardReceivablesMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Automobile [Member] | Consumer Non Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 11,505us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_AutomobileMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 11,505us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_AutomobileMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Automobile [Member] | Consumer Non Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 95us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_AutomobileMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 93us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_AutomobileMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Automobile [Member] | Consumer Non Real Estate [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 114us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_AutomobileMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 128us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_AutomobileMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Other Consumer Loans [Member] | Consumer Non Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 10,977us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_OtherConsumerLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 10,745us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_OtherConsumerLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Other Consumer Loans [Member] | Consumer Non Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 8us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_OtherConsumerLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		  
Other Consumer Loans [Member] | Consumer Non Real Estate [Member] | Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 5us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_OtherConsumerLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 6us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= nksh_OtherConsumerLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember
Real Estate Construction [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 41,647us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_RealEstateConstructionMember		 45,562us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_RealEstateConstructionMember
Consumer Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 144,891us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember		 146,221us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember
Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 308,325us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember		 297,138us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember
Commercial Non Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 31,510us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember		 32,734us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialNonRealEstateMember
Public Sector and IDA [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 53,441us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_PublicSectorAndIdaMember		 41,361us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_PublicSectorAndIdaMember
Consumer Non Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 28,204us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember		 28,182us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerNonRealEstateMember
Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 592,765us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 575,613us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans 4,279us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 5,300us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Classified Excluding Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Non-impaired gross loans $ 10,974us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember		 $ 10,285us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_InternalCreditAssessmentAxis
= nksh_ClassifiedExcludingImpairedMember