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

Amount of gain (loss) due to change in discount rate from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

No definition available.

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

Amount of gain (loss) due to change in mortality table from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

No definition available.

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

Amount of gain (loss) due to demographic changes from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

No definition available.

Name:	nksh_DefinedBenefitPlanBenefitObligationActuarialGainLossDueToDemographicChanges
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI https://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

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

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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929