Note 2 - Business Combination (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	Jun. 01, 2024	May 31, 2024
Share Price (in dollars per share)		$ 30.76
Frontier Community Bank [Member]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares (in shares)	464,855
Business Acquisition, Share Price (in dollars per share)	$ 30.76
Business Acquisition, Cash Payment, Maximum Percentage of Consideration (in dollars per share)	$ 10
Payment for Shareholder Elections and Fractional Shares	$ 1,769
Business Acquisition, Outstanding and Vested Options Settlement Payment	$ 281
Frontier Community Bank [Member] \| FCB Common Share [Member]
Business Acquisition, Share Price for Cash Payment of Fractional Shares and Option Settlement (in dollars per share)	$ 14.48

Maximum amount of consideration can be paid in cash under business acquisition as percentage.

No definition available.

Name:	nksh_BusinessAcquisitionCashPaymentMaximumPercentageOfConsideration
Namespace Prefix:	nksh_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Payment of Outstanding and vested options settlement amount under business acquisition.

+ References

No definition available.

+ Details

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

- Definition

Price of a single share for cash payment of fractional shares and option settlement under business acquisition.

+ References

No definition available.

+ Details

Name:	nksh_BusinessAcquisitionSharePriceForCashPaymentOfFractionalSharesAndOptionSettlement
Namespace Prefix:	nksh_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Cash outflow for shareholder elections and fractional shares.

+ References

No definition available.

+ Details

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

- Definition

Number of shares of equity interests issued or issuable to acquire entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 805
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(4)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479581/805-30-50-1

+ Details

Name:	us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

+ References

No definition available.

+ Details

Name:	us-gaap_BusinessAcquisitionSharePrice
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_BusinessAcquisitionAxis=nksh_FrontierCommunityBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=nksh_FcbCommonShareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: