Name:	nksh_AccruedExpensesForSalaryContinuationPlan
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

No definition available.

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

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

No definition available.

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

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

No definition available.

Name:	nksh_PercentageOfAllocatedEsopSharesThatCanBeDiversified
Namespace Prefix:	nksh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

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

No definition available.

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

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/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Name:	us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

Amount of discretionary contributions made by an employer to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Amount of expense for employee benefit and equity-based compensation.

No definition available.

Name:	us-gaap_EmployeeBenefitsAndShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480489/718-40-50-1

Name:	us-gaap_EmployeeStockOwnershipPlanESOPCashContributionsToESOP
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480489/718-40-50-1