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Note 3 - Securities - Realized Gains and Losses From Calls of Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Sale of Available for Sale Securities, proceeds	$ 9,279	$ 43,518
Sale of Available for Sale Securities, book value	9,279	46,850
Sale of Available for Sale Securities, gross gain	0	137
Sale of Available for Sale Securities, gross loss	0	3,469
Sale of Available for Sale Securities, net gain (loss)	$ 0	$ 3,332

X

- Definition

Book value of available-for-sale securities that were called during the period.

+ References

No definition available.

+ Details

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

X

- Definition

The gross realized gain on available-for-sale securities that were called during the period.

+ References

No definition available.

+ Details

Name:	nksh_AvailableforsaleSecuritiesGrossRealizedGainCalled
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

The gross realized gain (loss) on available-for-sale securities that were called during the period.

+ References

No definition available.

+ Details

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

X

- Definition

The gross realized loss on available-for-sale securities that were called during the period.

+ References

No definition available.

+ Details

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

X

- Definition

The cash inflow associated with calls (requests of early payments) on securities not classified as either held-to-maturity securities or trading securities which are classified as available-for-sale securities.

+ References

No definition available.

+ Details

Name:	nksh_ProceedsFromCallsOfAvailableforsaleSecurities
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration