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

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

No definition available.

Name:	nksh_DefinedBenefitPlanBenefitObligationActuarialGainLossDueToChangesInMortality
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

Amount of actuarial gain loss with asset return for benefit obligation of defined benefit plan.

No definition available.

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

Amount of gain loss due to asset return for benefit obligation of defined benefit plan

No definition available.

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

Amount of gain (loss) 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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1