Name:	nksh_AvailableForSaleAndHeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for securities.

No definition available.

Name:	nksh_ContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

This item represents the aggregate fair value of investments in debt and equity securities that have been in a continuous unrealized loss position for twelve months or longer.

No definition available.

Name:	nksh_ContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	nksh_Note5SecuritiesDetailsLineItems
Namespace Prefix:	nksh_
Data Type:	xbrli:stringItemType
Balance Type:	na
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 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.