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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

$ 15,192us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment

^[1],[2]

$ 13,075us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment

^[1],[2]

$ 16,311us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment

^[1]

Interest income recognized

174us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod

^[2]

99us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod

^[2]

473us-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

501us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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^[1],[2]

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^[1],[2]

Interest income recognized

7us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_ConsumerRealEstateMember

^[2]

4us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_ClosedEndFirstLiensMember
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= 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

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^[1],[2]

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^[1],[2]

Interest income recognized

4us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_ClosedEndJuniorLiensMember
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= nksh_ConsumerRealEstateMember

^[2]

5us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= 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

76us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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= nksh_InvestorOwnedResidentialRealEstateMember
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= nksh_ConsumerRealEstateMember

^[1],[2]

79us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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= nksh_InvestorOwnedResidentialRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_ConsumerRealEstateMember

^[1],[2]

Interest income recognized

1us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_InvestorOwnedResidentialRealEstateMember
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= nksh_ConsumerRealEstateMember

^[2]

1us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_InvestorOwnedResidentialRealEstateMember
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= 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

2,708us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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= nksh_CommercialRealEstateLoansMember

^[1],[2]

3,386us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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= nksh_MultifamilyRealEstateMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= nksh_CommercialRealEstateLoansMember

^[1],[2]

Interest income recognized

25us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_MultifamilyRealEstateMember
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= 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

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= nksh_CommercialRealEstateOwnerOccupiedMember
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= nksh_CommercialRealEstateLoansMember

^[1],[2]

5,515us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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= nksh_CommercialRealEstateOwnerOccupiedMember
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= nksh_CommercialRealEstateLoansMember

^[1],[2]

Interest income recognized

58us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_CommercialRealEstateOwnerOccupiedMember
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= nksh_CommercialRealEstateLoansMember

^[2]

44us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_CommercialRealEstateOwnerOccupiedMember
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= 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

6,023us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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= nksh_CommercialRealEstateOtherMember
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= nksh_CommercialRealEstateLoansMember

^[1],[2]

Interest income recognized

80us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_CommercialRealEstateOtherMember
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= 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

674us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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= nksh_CommercialAndIndustrialMember
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= nksh_CommercialNonRealEstateMember

^[1],[2]

Interest income recognized

(1)us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_CommercialAndIndustrialMember
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= 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

3,150us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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= nksh_ConstructionOtherMember
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= nksh_RealEstateConstructionMember

^[1],[2]

Interest income recognized

44us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= 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

101us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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= nksh_CommercialMember
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^[1],[2]

Interest income recognized

1us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
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= nksh_CommercialMember
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= 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

26us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
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= 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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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524



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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5258-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)(2)

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