Name:	nksh_AccruedExpensesForSalaryContinuationPlan
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Age of an employee to be eligible for the Employee Stock Ownership Plan (ESOP).

No definition available.

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Age required to diversify allocated Employee Stock Ownership Plan (ESOP) shares.

No definition available.

Name:	nksh_AgeOfEmployeesRequiredToDiversifyAllocatedEsopShares
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Percentage of allocated Employee Stock Ownership Plan shares that can diversified.

No definition available.

Name:	nksh_PercentageOfAllocatedEsopSharesThatCanBeDiversified
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Years of plan participation required to diversify Employee Stock Ownership Plan (ESOP).

No definition available.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
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Amount of discretionary contributions made by an employer to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
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Data Type:	xbrli:monetaryItemType
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Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
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This item represents the amount of cash contributions during the period made by the entity to the Employee Stock Ownership Plan (ESOP).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=65895303&loc=d3e17540-113929

Name:	us-gaap_EmployeeStockOwnershipPlanESOPCashContributionsToESOP
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The shares or units in an ESOP trust that have been assigned to individual participant accounts based on a known formula. IRS rules require allocations to be nondiscriminatory generally based on compensation, length of service, or a combination of both. For any particular participant such shares or units may be vested, unvested, or partially vested.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=65895303&loc=d3e17540-113929

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Data Type:	xbrli:sharesItemType
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Period Type:	instant

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Namespace Prefix:
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