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Note 15 - Fair Value Measurements (Details Textual) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2022 | Dec. 31, 2021 | Dec. 31, 2022
Threshold for Designation to Impaired Status |  |  | $ 250
Residential Portfolio Segment [Member] | Multifamily Real Estate [Member] |  |  |
Threshold for Designation to Impaired Status |  |  | 250
Commercial Real Estate Portfolio Segment [Member] |  |  |
Threshold for Designation to Impaired Status |  |  | 500
Loans Held-for-sale [Member] | Changes Measurement [Member] | Fair Value, Nonrecurring [Member] |  |  |
Assets, Fair Value Adjustment | $ 0 | $ 0 |
Interest Rate Contract [Member] |  |  |
Derivative, Fair Value, Net, Total |  | 0 | $ 0
Forward Contract [Member] |  |  |
Derivative, Fair Value, Net, Total |  | $ 0 |

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- Definition This is threshold for designation to impaired status for loan relationship that are non accrual, significantly past due, display credit weakness or are TDR. + References No definition available. + Details
Name: | nksh_ThresholdForDesignationToImpairedStatus
Namespace Prefix: | nksh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Amount of addition (reduction) to the amount at which an asset could be incurred (settled) in a current transaction between willing parties. + References No definition available. + Details
Name: | us-gaap_AssetsFairValueAdjustment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI https://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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

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

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

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

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

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