Name:	nksh_AvailableForSaleAndHeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Details

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Period Type:	duration

This item contains disclosure of the number of investment positions determined to be temporarily impaired.

No definition available.

Name:	nksh_NumberOfTemporarilyImpairedSecurities
Namespace Prefix:	nksh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The fair value of available-for-sale securities that serve as collateral for borrowings.

Name:	us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Reflects the aggregate value of loans, trade receivables, securities and financial instruments that serve as collateral for obligations arising from a transfer of financial assets recorded as a secured borrowing.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5086-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7523297&loc=SL6224234-111729

Name:	us-gaap_LoansAndLeasesReceivableCollateralForSecuredBorrowings
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Period Type:	instant

Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

No definition available.

Name:	us-gaap_RestrictedInvestments
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Period Type:	instant

The increase (decrease), resulting in a loss, in the difference between the fair value and the carrying value, or in the comparative fair values, of securities held at each balance sheet date, that was included in earnings for the period.

No definition available.