Note 3 - Securities - Realized Gains and Losses From Calls of Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Available for sale, proceeds	$ 20,377	$ 126,840
Available for sale, book value	20,371	126,732
Available for sale, gross gain	6	110
Available for sale, gross loss	0	2
Available for sale, net gain (loss)	$ 6	$ 108

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

No definition available.

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Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	nksh_AvailableforsaleSecuritiesGrossRealizedGainCalled
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

- Definition

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

+ References

No definition available.

+ Details

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

- 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

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration