Amount of principal forgiven in a troubled debt restructuring agreement.

No definition available.

Name:	nksh_FinancingReceivableModificationsPrincipalForgiven
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Increase in the percentage of allocation for loans rated classified.

+ References

No definition available.

+ Details

Name:	nksh_IncreaseInPercentageOfAllocationLoansRatedClassified
Namespace Prefix:	nksh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Increase in the percentage of allocation for loans rated special mention.

+ References

No definition available.

+ Details

Name:	nksh_IncreaseInPercentageOfAllocationLoansRatedSpecialMention
Namespace Prefix:	nksh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	nksh_Note5AllowanceforLoanLossesNonperformingAssetsandImpairedLoansDetailsLineItems
Namespace Prefix:	nksh_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the threshold period for considering loans as special mention or classified.

+ References

No definition available.

+ Details

Name:	nksh_ThresholdPeriodForConsideringLoansAsSpecialMentionOrClassified
Namespace Prefix:	nksh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of allowance for credit losses related to receivables which had been measured under a general allowance for credit losses methodology that are now identified as troubled debt restructurings.

+ References

No definition available.

+ Details

Name:	us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate interest and fee income generated by: (1) loans the Entity has positive intent and ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (a) industrial and agricultural; (b) real estate; and (c) real estate construction loans; (d) trade financing; (e) lease financing; (f) home equity lines-of-credit; (g) automobile and other vehicle loans; and (h) credit card and other revolving-type loans and (2) loans and leases held-for-sale which may include mortgage loans, direct financing, and sales-type leases.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.1)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

Name:	us-gaap_InterestAndFeeIncomeLoansAndLeases
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_SpecialMentionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=nksh_ClassifiedExcludingImpairedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_NonperformingFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=nksh_CommercialRealEstateOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=nksh_ForgivePrincipalReduceInterestRateCapitalizeInterestAndReamortizePaymentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=nksh_InterestOnlyPaymentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ContractualInterestRateReductionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=nksh_CommercialRealEstateNonownerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=nksh_RealEstateConstructionPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=nksh_BecomeNonrevolvingAndInterestOnlyPaymentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Interest and Fee Income, Loans and Leases (in Dollars)		$ 30,446	$ 31,058	$ 32,484
Threshold Period for Considering Loans As Special Mention Or Classified		75 days
Financing Receivable, Modifications, Number of Contracts		6	5
Allowance for Credit Losses, Change in Method of Calculating Impairment (in Dollars)			$ 206
Financing Receivable, Modifications, Subsequent Default, Number of Contracts		0	0
Special Mention [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Increase in Percentage of Allocation Loans Rated Special Mention		50.00%
Classified Excluding Impaired [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Increase in Percentage of Allocation Loans Rated Classified		100.00%
Nonperforming Financial Instruments [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Interest and Fee Income, Loans and Leases (in Dollars)		$ 0	$ 0	$ 0
Commercial Real Estate Portfolio Segment [Member] \| Commercial Real Estate, Owner Occupied [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Financing Receivable, Modifications, Number of Contracts		3	1
Commercial Real Estate Portfolio Segment [Member] \| Commercial Real Estate, Owner Occupied [Member] \| Forgive Principal, Reduce Interest Rate, Capitalize Interest, and Re-amortize Payments [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Financing Receivable, Modifications, Number of Contracts		1
Financing Receivable, Modifications, Principal Forgiven (in Dollars)		$ 100
Allowance for Credit Losses, Change in Method of Calculating Impairment (in Dollars)	$ 0	0
Commercial Real Estate Portfolio Segment [Member] \| Commercial Real Estate, Owner Occupied [Member] \| Interest Only Payments [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Financing Receivable, Modifications, Number of Contracts	2
Allowance for Credit Losses, Change in Method of Calculating Impairment (in Dollars)	$ 23	23
Commercial Real Estate Portfolio Segment [Member] \| Commercial Real Estate, Owner Occupied [Member] \| Contractual Interest Rate Reduction [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Financing Receivable, Modifications, Number of Contracts			2
Commercial Real Estate Portfolio Segment [Member] \| Commercial Real Estate Non-owner Occupied [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Financing Receivable, Modifications, Number of Contracts			2
Commercial Real Estate Portfolio Segment [Member] \| Commercial Real Estate Non-owner Occupied [Member] \| Interest Only Payments [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Financing Receivable, Modifications, Number of Contracts			2
Real Estate Construction Portfolio Segment[Member] \| Become Non-revolving and Interest Only Payments [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Financing Receivable, Modifications, Number of Contracts	2
Allowance for Credit Losses, Change in Method of Calculating Impairment (in Dollars)	$ 0	0
Commercial Portfolio Segment [Member] \| Extended Maturity [Member]
Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) [Line Items]
Financing Receivable, Modifications, Number of Contracts	1
Allowance for Credit Losses, Change in Method of Calculating Impairment (in Dollars)	$ 0	$ 0