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Note 10 - Restrictions on Dividends (Details Textual) - USD ($) | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Consolidated Subsidiaries | $ 20,000,000 | $ 12,000,000
Period of Restriction on Retained Net Income Without Prior Approval (Year) | 2 years |
Minimum [Member] |  |
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval | $ 5,743,000 |

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- Definition Period of restrictions on banking or savings institution's ability to pay dividends. + References No definition available. + Details
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Namespace Prefix: | nksh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Amount of dividends that can be declared or paid without approval of regulatory agency. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Data Type: | na
Balance Type: |
Period Type: |