<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.26.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>310</ContextCount>
  <ElementCount>268</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>60</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>9</UnitCount>
  <MyReports>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0000001 - Document - Cover page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/Coverpage</Role>
      <ShortName>Cover page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>9952151 - Statement - Consolidated Statements of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ConsolidatedStatementsofOperations</Role>
      <ShortName>Consolidated Statements of Operations</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>9952152 - Statement - Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ConsolidatedStatementsofComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>9952153 - Statement - Consolidated Statements of Comprehensive Income (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ConsolidatedStatementsofComprehensiveIncomeParentheticals</Role>
      <ShortName>Consolidated Statements of Comprehensive Income (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>9952154 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>9952155 - Statement - Consolidated Balance Sheets (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ConsolidatedBalanceSheetsParentheticals</Role>
      <ShortName>Consolidated Balance Sheets (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>9952156 - Statement - Consolidated Statements of Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ConsolidatedStatementsofEquity</Role>
      <ShortName>Consolidated Statements of Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>9952157 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ConsolidatedStatementsofCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>9952158 - Disclosure - Background</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/Background</Role>
      <ShortName>Background</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>9952159 - Disclosure - Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/BasisofPresentation</Role>
      <ShortName>Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>9952160 - Disclosure - New Accounting Standards</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/NewAccountingStandards</Role>
      <ShortName>New Accounting Standards</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>9952161 - Disclosure - Receivables and Allowance for Expected Credit Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ReceivablesandAllowanceforExpectedCreditLosses</Role>
      <ShortName>Receivables and Allowance for Expected Credit Losses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>9952162 - Disclosure - Inventories</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/Inventories</Role>
      <ShortName>Inventories</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>9952163 - Disclosure - Net Loss Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/NetLossPerShare</Role>
      <ShortName>Net Loss Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>9952164 - Disclosure - Accumulated other comprehensive loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/Accumulatedothercomprehensiveloss</Role>
      <ShortName>Accumulated other comprehensive loss</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>9952165 - Disclosure - Revenue from Contracts with Customers</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/RevenuefromContractswithCustomers</Role>
      <ShortName>Revenue from Contracts with Customers</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>9952166 - Disclosure - Uncompleted Contracts</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/UncompletedContracts</Role>
      <ShortName>Uncompleted Contracts</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>9952167 - Disclosure - Acquisitions and Dispositions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/AcquisitionsandDispositions</Role>
      <ShortName>Acquisitions and Dispositions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>9952168 - Disclosure - Goodwill and Other Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/GoodwillandOtherIntangibleAssets</Role>
      <ShortName>Goodwill and Other Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>9952169 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>9952170 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/Debt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>9952171 - Disclosure - Cash Flow Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/CashFlowInformation</Role>
      <ShortName>Cash Flow Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>9952172 - Disclosure - Business Segment Data</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/BusinessSegmentData</Role>
      <ShortName>Business Segment Data</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>9952173 - Disclosure - Commitments and contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/Commitmentsandcontingencies</Role>
      <ShortName>Commitments and contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>9955511 - Disclosure - Basis of Presentation (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/BasisofPresentationPolicies</Role>
      <ShortName>Basis of Presentation (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/NewAccountingStandards</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>9955512 - Disclosure - Basis of Presentation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/BasisofPresentationTables</Role>
      <ShortName>Basis of Presentation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/BasisofPresentation</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>9955513 - Disclosure - New Accounting Standards (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/NewAccountingStandardsTables</Role>
      <ShortName>New Accounting Standards (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/NewAccountingStandards</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>9955514 - Disclosure - Receivables and Allowance for Expected Credit Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ReceivablesandAllowanceforExpectedCreditLossesTables</Role>
      <ShortName>Receivables and Allowance for Expected Credit Losses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/ReceivablesandAllowanceforExpectedCreditLosses</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>9955515 - Disclosure - Inventories (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/InventoriesTables</Role>
      <ShortName>Inventories (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/Inventories</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>9955516 - Disclosure - Net Loss Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/NetLossPerShareTables</Role>
      <ShortName>Net Loss Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/NetLossPerShare</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>9955517 - Disclosure - Revenue from Contracts with Customers (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/RevenuefromContractswithCustomersTables</Role>
      <ShortName>Revenue from Contracts with Customers (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/RevenuefromContractswithCustomers</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>9955518 - Disclosure - Uncompleted Contracts (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/UncompletedContractsTables</Role>
      <ShortName>Uncompleted Contracts (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/UncompletedContracts</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>9955519 - Disclosure - Goodwill and Other Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/GoodwillandOtherIntangibleAssetsTables</Role>
      <ShortName>Goodwill and Other Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/GoodwillandOtherIntangibleAssets</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>9955520 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/FairValueMeasurements</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>9955521 - Disclosure - Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/DebtTables</Role>
      <ShortName>Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/Debt</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>9955522 - Disclosure - Cash Flow Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/CashFlowInformationTables</Role>
      <ShortName>Cash Flow Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/CashFlowInformation</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>9955523 - Disclosure - Business Segment Data (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/BusinessSegmentDataTables</Role>
      <ShortName>Business Segment Data (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/BusinessSegmentData</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>9955524 - Disclosure - Background (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/BackgroundDetails</Role>
      <ShortName>Background (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/Background</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>9955525 - Disclosure - Basis of Presentation - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/BasisofPresentationNarrativeDetails</Role>
      <ShortName>Basis of Presentation - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>9955526 - Disclosure - Basis of Presentation - Schedule of Cash and Cash Equivalents (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/BasisofPresentationScheduleofCashandCashEquivalentsDetails</Role>
      <ShortName>Basis of Presentation - Schedule of Cash and Cash Equivalents (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>9955527 - Disclosure - Receivables and Allowance for Expected Credit Losses - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ReceivablesandAllowanceforExpectedCreditLossesNarrativeDetails</Role>
      <ShortName>Receivables and Allowance for Expected Credit Losses - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/ReceivablesandAllowanceforExpectedCreditLossesTables</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>9955528 - Disclosure - Receivables and Allowance for Expected Credit Losses - Schedule of Receivables (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ReceivablesandAllowanceforExpectedCreditLossesScheduleofReceivablesDetails</Role>
      <ShortName>Receivables and Allowance for Expected Credit Losses - Schedule of Receivables (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>9955529 - Disclosure - Receivables and Allowance for Expected Credit Losses - Schedule of Details of Expected Credit Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/ReceivablesandAllowanceforExpectedCreditLossesScheduleofDetailsofExpectedCreditLossesDetails</Role>
      <ShortName>Receivables and Allowance for Expected Credit Losses - Schedule of Details of Expected Credit Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>9955530 - Disclosure - Inventories (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/InventoriesDetails</Role>
      <ShortName>Inventories (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/InventoriesTables</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>9955531 - Disclosure - Net Loss Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/NetLossPerShareDetails</Role>
      <ShortName>Net Loss Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/NetLossPerShareTables</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>9955532 - Disclosure - Accumulated other comprehensive loss (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/AccumulatedothercomprehensivelossDetails</Role>
      <ShortName>Accumulated other comprehensive loss (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/Accumulatedothercomprehensiveloss</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>9955533 - Disclosure - Revenue from Contracts with Customers (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/RevenuefromContractswithCustomersDetails</Role>
      <ShortName>Revenue from Contracts with Customers (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/RevenuefromContractswithCustomersTables</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>9955534 - Disclosure - Uncompleted Contracts - Schedule of Changes in Contract Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/UncompletedContractsScheduleofChangesinContractAssetsandLiabilitiesDetails</Role>
      <ShortName>Uncompleted Contracts - Schedule of Changes in Contract Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>9955535 - Disclosure - Uncompleted Contracts - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/UncompletedContractsNarrativeDetails</Role>
      <ShortName>Uncompleted Contracts - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>9955536 - Disclosure - Acquisitions and Dispositions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/AcquisitionsandDispositionsDetails</Role>
      <ShortName>Acquisitions and Dispositions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/AcquisitionsandDispositions</ParentRole>
      <Position>51</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>9955537 - Disclosure - Goodwill and Other Intangible Assets - Schedule of Changes in the Carrying Amount of Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/GoodwillandOtherIntangibleAssetsScheduleofChangesintheCarryingAmountofGoodwillDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Schedule of Changes in the Carrying Amount of Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>9955538 - Disclosure - Goodwill and Other Intangible Assets - Schedule of Other Amortizable Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/GoodwillandOtherIntangibleAssetsScheduleofOtherAmortizableIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Schedule of Other Amortizable Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>9955539 - Disclosure - Goodwill and Other Intangible Assets - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/GoodwillandOtherIntangibleAssetsNarrativeDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>9955540 - Disclosure - Goodwill and Other Intangible Assets - Schedule of Estimated Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/GoodwillandOtherIntangibleAssetsScheduleofEstimatedAmortizationExpenseDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Schedule of Estimated Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>9955541 - Disclosure - Fair Value Measurements - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/FairValueMeasurementsNarrativeDetails</Role>
      <ShortName>Fair Value Measurements - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>9955542 - Disclosure - Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/FairValueMeasurementsScheduleofAssetsMeasuredatFairValueonaRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>9955543 - Disclosure - Fair Value Measurements - Schedule of Fair Value of Long-Term Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/FairValueMeasurementsScheduleofFairValueofLongTermDebtDetails</Role>
      <ShortName>Fair Value Measurements - Schedule of Fair Value of Long-Term Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>9955544 - Disclosure - Debt - Schedule of Long-Term Debt Outstanding (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/DebtScheduleofLongTermDebtOutstandingDetails</Role>
      <ShortName>Debt - Schedule of Long-Term Debt Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>9955545 - Disclosure - Debt - Schedule of Debt Maturities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/DebtScheduleofDebtMaturitiesDetails</Role>
      <ShortName>Debt - Schedule of Debt Maturities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>9955546 - Disclosure - Cash Flow Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/CashFlowInformationDetails</Role>
      <ShortName>Cash Flow Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/CashFlowInformationTables</ParentRole>
      <Position>61</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>9955547 - Disclosure - Business Segment Data - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/BusinessSegmentDataNarrativeDetails</Role>
      <ShortName>Business Segment Data - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>9955548 - Disclosure - Business Segment Data - Schedule of Segment Reporting Information, by Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/BusinessSegmentDataScheduleofSegmentReportingInformationbySegmentDetails</Role>
      <ShortName>Business Segment Data - Schedule of Segment Reporting Information, by Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="knf-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>9955549 - Disclosure - Commitments and contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.kniferiver.com/role/CommitmentsandcontingenciesDetails</Role>
      <ShortName>Commitments and contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.kniferiver.com/role/Commitmentsandcontingencies</ParentRole>
      <Position>64</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" isDefinitelyFs="true" isUsgaap="true" original="knf-20260331.htm">knf-20260331.htm</File>
    <File>knf-20260331.xsd</File>
    <File>knf-20260331_cal.xml</File>
    <File>knf-20260331_def.xml</File>
    <File>knf-20260331_lab.xml</File>
    <File>knf-20260331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="899">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="30">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
