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

- Definition

This is threshold for designation to impaired status for loan relationship that are non accrual, significantly past due, display credit weakness or are TDR.

+ References

No definition available.

+ Details

Name:	nksh_ThresholdForDesignationToImpairedStatus
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
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=66008989&loc=SL6953676-111524

+ Details

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

- Definition

The amount of the outstanding recorded investment related to 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 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

+ Details

Name:	us-gaap_FinancingReceivableModificationsRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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=66008989&loc=SL6953682-111524

+ Details

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

- Definition

The amount of financing receivables reclassified to held for sale during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableReclassificationToHeldForSale
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

- Definition

Value of loans held-for-sale transferred to loans held in the entity's portfolio in noncash transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

+ Details

Name:	us-gaap_TransferOfLoansHeldForSaleToPortfolioLoans1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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_CommercialRealEstateOtherMember
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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=nksh_CommercialRealEstateOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- 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:

Note 4 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details Textual)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Nonperforming Financial Instruments [Member]
Interest and Fee Income, Loans and Leases			$ 0	$ 0	$ 0
Commercial Real Estate Portfolio Segment [Member] \| Commercial Real Estate Other [Member] \| Forgive Principal, Reduce Interest Rate, Capitalize Interest, and Re-amortize Payments [Member]
Allowance for Credit Losses, Change in Method of Calculating Impairment	$ 0		$ 0
Commercial Real Estate Portfolio Segment [Member] \| Commercial Real Estate Other [Member]
Financing Receivable, Modifications, Number of Contracts	2		2
Commercial Real Estate Portfolio Segment [Member] \| Commercial Real Estate, Owner Occupied [Member] \| Forgive Principal, Reduce Interest Rate, Capitalize Interest, and Re-amortize Payments [Member]
Allowance for Credit Losses, Change in Method of Calculating Impairment		$ 0		0
Financing Receivable Modifications Principal Forgiven				$ 100,000
Commercial Real Estate Portfolio Segment [Member] \| Commercial Real Estate, Owner Occupied [Member]
Financing Receivable, Modifications, Number of Contracts				1
Special Mention [Member]
Increase in Percentage of Allocation Loans Rated Special Mention			50.00%
Classified Excluding Impaired [Member]
Increase in Percentage of Allocation Loans Rated Classified			100.00%
Interest and Fee Income, Loans and Leases	$ 7,289,000	$ 7,600,000	$ 14,623,000	$ 15,210,000
Financing Receivable, Reclassification to Held-for-sale			0
Transfer of Loans Held-for-sale to Portfolio Loans			$ 0
Financing Receivable, Modifications, Subsequent Default, Number of Contracts			0	0
Financing Receivable, Modifications, Number of Contracts	2	0	2	1
Threshold for Designation to Impaired Status			$ 250,000
Threshold Period for Considering Loans as Special Mention or Classified			75 days
Financing Receivable, Modifications, Recorded Investment	$ 9,183,000	$ 11,978,000	$ 9,183,000	$ 11,978,000	$ 13,453,000