<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.4</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>541</ContextCount>
  <ElementCount>612</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>142</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>12</UnitCount>
  <MyReports>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001001 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001002 - Statement - CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/CONSOLIDATEDBALANCESHEETS</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1002003 - Statement - CONSOLIDATED BALANCE SHEETS (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/CONSOLIDATEDBALANCESHEETSParentheticals</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1003004 - Statement - CONSOLIDATED STATEMENTS OF NET INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/CONSOLIDATEDSTATEMENTSOFNETINCOME</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF NET INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1004005 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1005006 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1006007 - Statement - CONSOLIDATED STATEMENTS OF EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/CONSOLIDATEDSTATEMENTSOFEQUITY</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>1007008 - Statement - CONSOLIDATED STATEMENTS OF EQUITY (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/CONSOLIDATEDSTATEMENTSOFEQUITYParentheticals</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF EQUITY (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2101101 - Disclosure - Summary of Significant Accounting Policies and Other Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SummaryofSignificantAccountingPoliciesandOtherInformation</Role>
      <ShortName>Summary of Significant Accounting Policies and Other Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2106102 - Disclosure - Acquisitions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/Acquisitions</Role>
      <ShortName>Acquisitions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2112103 - Disclosure - Inventories</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/Inventories</Role>
      <ShortName>Inventories</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2115104 - Disclosure - Property, Plant, and Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/PropertyPlantandEquipment</Role>
      <ShortName>Property, Plant, and Equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2118105 - Disclosure - Goodwill and Other Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/GoodwillandOtherIntangibleAssets</Role>
      <ShortName>Goodwill and Other Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2124106 - Disclosure - Accrued Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/AccruedLiabilities</Role>
      <ShortName>Accrued Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2127107 - Disclosure - Lease Commitments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/LeaseCommitments</Role>
      <ShortName>Lease Commitments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2134108 - Disclosure - Restructuring, Impairment and Other Charges</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/RestructuringImpairmentandOtherCharges</Role>
      <ShortName>Restructuring, Impairment and Other Charges</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2137109 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/Debt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2142110 - Disclosure - Fair Value of Assets and Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/FairValueofAssetsandLiabilities</Role>
      <ShortName>Fair Value of Assets and Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2148111 - Disclosure - Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlans</Role>
      <ShortName>Benefit Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2161112 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/StockBasedCompensation</Role>
      <ShortName>Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2167113 - Disclosure - Other Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/OtherComprehensiveIncomeLoss</Role>
      <ShortName>Other Comprehensive Income (Loss)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2172114 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2179115 - Disclosure - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/EarningsPerShare</Role>
      <ShortName>Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2183116 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2188117 - Disclosure - Selected Quarterly Financial Data (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SelectedQuarterlyFinancialDataUnaudited</Role>
      <ShortName>Selected Quarterly Financial Data (Unaudited)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2192118 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/RelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2195119 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2197120 - Disclosure - Schedule II - Valuation and Qualifying Accounts and Reserves</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/ScheduleIIValuationandQualifyingAccountsandReserves</Role>
      <ShortName>Schedule II - Valuation and Qualifying Accounts and Reserves</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2202201 - Disclosure - Summary of Significant Accounting Policies and Other Information (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SummaryofSignificantAccountingPoliciesandOtherInformationPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies and Other Information (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/SummaryofSignificantAccountingPoliciesandOtherInformation</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2303301 - Disclosure - Summary of Significant Accounting Policies and Other Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SummaryofSignificantAccountingPoliciesandOtherInformationTables</Role>
      <ShortName>Summary of Significant Accounting Policies and Other Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/SummaryofSignificantAccountingPoliciesandOtherInformation</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2307302 - Disclosure - Acquisitions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/AcquisitionsTables</Role>
      <ShortName>Acquisitions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/Acquisitions</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2313303 - Disclosure - Inventories (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/InventoriesTables</Role>
      <ShortName>Inventories (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/Inventories</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2316304 - Disclosure - Property, Plant, and Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/PropertyPlantandEquipmentTables</Role>
      <ShortName>Property, Plant, and Equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/PropertyPlantandEquipment</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2319305 - Disclosure - Goodwill and Other Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/GoodwillandOtherIntangibleAssetsTables</Role>
      <ShortName>Goodwill and Other Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/GoodwillandOtherIntangibleAssets</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2325306 - Disclosure - Accrued Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/AccruedLiabilitiesTables</Role>
      <ShortName>Accrued Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/AccruedLiabilities</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2328307 - Disclosure - Lease Commitments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/LeaseCommitmentsTables</Role>
      <ShortName>Lease Commitments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/LeaseCommitments</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2335308 - Disclosure - Restructuring, Impairment and Other Charges (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/RestructuringImpairmentandOtherChargesTables</Role>
      <ShortName>Restructuring, Impairment and Other Charges (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/RestructuringImpairmentandOtherCharges</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2338309 - Disclosure - Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/DebtTables</Role>
      <ShortName>Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/Debt</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2343310 - Disclosure - Fair Value of Assets and Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/FairValueofAssetsandLiabilitiesTables</Role>
      <ShortName>Fair Value of Assets and Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/FairValueofAssetsandLiabilities</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2349311 - Disclosure - Benefit Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansTables</Role>
      <ShortName>Benefit Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/BenefitPlans</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2362312 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/StockBasedCompensationTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/StockBasedCompensation</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2368313 - Disclosure - Other Comprehensive Income (Loss) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/OtherComprehensiveIncomeLossTables</Role>
      <ShortName>Other Comprehensive Income (Loss) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/OtherComprehensiveIncomeLoss</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2373314 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/IncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/IncomeTaxes</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2380315 - Disclosure - Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/EarningsPerShareTables</Role>
      <ShortName>Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/EarningsPerShare</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2384316 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/SegmentInformation</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2389317 - Disclosure - Selected Quarterly Financial Data (Unaudited) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SelectedQuarterlyFinancialDataUnauditedTables</Role>
      <ShortName>Selected Quarterly Financial Data (Unaudited) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/SelectedQuarterlyFinancialDataUnaudited</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2393318 - Disclosure - Related Party Disclosures (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/RelatedPartyDisclosuresTables</Role>
      <ShortName>Related Party Disclosures (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2404401 - Disclosure - Summary of Significant Accounting Policies and Other Information - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SummaryofSignificantAccountingPoliciesandOtherInformationNarrativeDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Other Information - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/SummaryofSignificantAccountingPoliciesandOtherInformationTables</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2405402 - Disclosure - Summary of Significant Accounting Policies and Other Information - Revenue Disaggregation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SummaryofSignificantAccountingPoliciesandOtherInformationRevenueDisaggregationDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Other Information - Revenue Disaggregation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2408403 - Disclosure - Acquisitions - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/AcquisitionsNarrativeDetails</Role>
      <ShortName>Acquisitions - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2409404 - Disclosure - Acquisitions - Preliminary Price Allocation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/AcquisitionsPreliminaryPriceAllocationDetails</Role>
      <ShortName>Acquisitions - Preliminary Price Allocation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2410405 - Disclosure - Acquisitions - Business Acquisition Pro Forma Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/AcquisitionsBusinessAcquisitionProFormaInformationDetails</Role>
      <ShortName>Acquisitions - Business Acquisition Pro Forma Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2411406 - Disclosure - Acquisitions - Pro Forma Information Adjustments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/AcquisitionsProFormaInformationAdjustmentsDetails</Role>
      <ShortName>Acquisitions - Pro Forma Information Adjustments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2414407 - Disclosure - Inventories - Components of Inventories (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/InventoriesComponentsofInventoriesDetails</Role>
      <ShortName>Inventories - Components of Inventories (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2417408 - Disclosure - Property, Plant, and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/PropertyPlantandEquipmentDetails</Role>
      <ShortName>Property, Plant, and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/PropertyPlantandEquipmentTables</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2420409 - Disclosure - Goodwill and Other Intangible Assets - Amounts for Goodwill and Changes in Carrying Value by Operating Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/GoodwillandOtherIntangibleAssetsAmountsforGoodwillandChangesinCarryingValuebyOperatingSegmentDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Amounts for Goodwill and Changes in Carrying Value by Operating Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2421410 - Disclosure - Goodwill and Other Intangible Assets - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/GoodwillandOtherIntangibleAssetsNarrativeDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2422411 - Disclosure - Goodwill and Other Intangible Assets - Details of Other Intangible Assets and Related Future Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/GoodwillandOtherIntangibleAssetsDetailsofOtherIntangibleAssetsandRelatedFutureAmortizationExpenseDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Details of Other Intangible Assets and Related Future Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2423412 - Disclosure - Goodwill and Other Intangible Assets - Estimated Amortization Expense Related to Intangible Assets with Definite Lives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/GoodwillandOtherIntangibleAssetsEstimatedAmortizationExpenseRelatedtoIntangibleAssetswithDefiniteLivesDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Estimated Amortization Expense Related to Intangible Assets with Definite Lives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2426413 - Disclosure - Accrued Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/AccruedLiabilitiesDetails</Role>
      <ShortName>Accrued Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/AccruedLiabilitiesTables</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2429414 - Disclosure - Lease Commitments - Balance Sheet, Operating Lease Term and Discount Rate (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/LeaseCommitmentsBalanceSheetOperatingLeaseTermandDiscountRateDetails</Role>
      <ShortName>Lease Commitments - Balance Sheet, Operating Lease Term and Discount Rate (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2430415 - Disclosure - Lease Commitments - Lease Cost (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/LeaseCommitmentsLeaseCostDetails</Role>
      <ShortName>Lease Commitments - Lease Cost (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2431416 - Disclosure - Lease Commitments - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/LeaseCommitmentsNarrativeDetails</Role>
      <ShortName>Lease Commitments - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2432417 - Disclosure - Lease Commitments - Maturities of Lease Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/LeaseCommitmentsMaturitiesofLeaseLiabilitiesDetails</Role>
      <ShortName>Lease Commitments - Maturities of Lease Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2433418 - Disclosure - Lease Commitments - Supplemental Cash Flow Information (Details) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/LeaseCommitmentsSupplementalCashFlowInformationDetailsDetails</Role>
      <ShortName>Lease Commitments - Supplemental Cash Flow Information (Details) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2436419 - Disclosure - Restructuring, Impairment and Other Charges (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/RestructuringImpairmentandOtherChargesDetails</Role>
      <ShortName>Restructuring, Impairment and Other Charges (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/RestructuringImpairmentandOtherChargesTables</ParentRole>
      <Position>66</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2439420 - Disclosure - Debt - Carrying Amounts of Long-term Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/DebtCarryingAmountsofLongtermDebtDetails</Role>
      <ShortName>Debt - Carrying Amounts of Long-term Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>2440421 - Disclosure - Debt - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/DebtNarrativeDetails</Role>
      <ShortName>Debt - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>2441422 - Disclosure - Debt - Scheduled Maturities of the Company's Long Term Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/DebtScheduledMaturitiesoftheCompanysLongTermDebtDetails</Role>
      <ShortName>Debt - Scheduled Maturities of the Company's Long Term Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>2444423 - Disclosure - Fair Value of Assets and Liabilities - Narratives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/FairValueofAssetsandLiabilitiesNarrativesDetails</Role>
      <ShortName>Fair Value of Assets and Liabilities - Narratives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>2445424 - Disclosure - Fair Value of Assets and Liabilities - Assets Measured at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/FairValueofAssetsandLiabilitiesAssetsMeasuredatFairValueDetails</Role>
      <ShortName>Fair Value of Assets and Liabilities - Assets Measured at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>2446425 - Disclosure - Fair Value of Assets and Liabilities - Carrying Value and Estimated Fair Value of Senior Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.littelfuse.com/role/FairValueofAssetsandLiabilitiesCarryingValueandEstimatedFairValueofSeniorNotesDetails</Role>
      <ShortName>Fair Value of Assets and Liabilities - Carrying Value and Estimated Fair Value of Senior Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>2447426 - Disclosure - Fair Value of Assets and Liabilities - Details of impairment of long-lived assets held and used by asset (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/FairValueofAssetsandLiabilitiesDetailsofimpairmentoflonglivedassetsheldandusedbyassetDetails</Role>
      <ShortName>Fair Value of Assets and Liabilities - Details of impairment of long-lived assets held and used by asset (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>2450427 - Disclosure - Benefit Plans - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansNarrativeDetails</Role>
      <ShortName>Benefit Plans - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>2451428 - Disclosure - Benefit Plans - Benefit Plan Related Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansBenefitPlanRelatedInformationDetails</Role>
      <ShortName>Benefit Plans - Benefit Plan Related Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>2452429 - Disclosure - Benefit Plans - Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Pre-tax (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossPretaxDetails</Role>
      <ShortName>Benefit Plans - Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Pre-tax (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>2453430 - Disclosure - Benefit Plans - Benefit Plan Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansBenefitPlanExpensesDetails</Role>
      <ShortName>Benefit Plans - Benefit Plan Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>2454431 - Disclosure - Benefit Plans - Weighted Average Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansWeightedAverageAssumptionsDetails</Role>
      <ShortName>Benefit Plans - Weighted Average Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>2455432 - Disclosure - Benefit Plans - Funded Status of Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansFundedStatusofPlansDetails</Role>
      <ShortName>Benefit Plans - Funded Status of Plans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>2456433 - Disclosure - Benefit Plans - Expected Benefit Payments to Be Paid to Participants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansExpectedBenefitPaymentstoBePaidtoParticipantsDetails</Role>
      <ShortName>Benefit Plans - Expected Benefit Payments to Be Paid to Participants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>2457434 - Disclosure - Benefit Plans - Allocation of Plan Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansAllocationofPlanAssetsDetails</Role>
      <ShortName>Benefit Plans - Allocation of Plan Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>2458435 - Disclosure - Benefit Plans - The Company's Pension Plan Assets Measured at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansTheCompanysPensionPlanAssetsMeasuredatFairValueDetails</Role>
      <ShortName>Benefit Plans - The Company's Pension Plan Assets Measured at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>2459436 - Disclosure - Benefit Plans - Fair Value Measurement of Plan Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansFairValueMeasurementofPlanAssetsDetails</Role>
      <ShortName>Benefit Plans - Fair Value Measurement of Plan Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>2460437 - Disclosure - Benefit Plans - Defined Contribution and Other Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/BenefitPlansDefinedContributionandOtherPlansDetails</Role>
      <ShortName>Benefit Plans - Defined Contribution and Other Plans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>2463438 - Disclosure - Stock-Based Compensation - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/StockBasedCompensationNarrativeDetails</Role>
      <ShortName>Stock-Based Compensation - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>2464439 - Disclosure - Stock-Based Compensation - Reconciliation of Outstanding Stock Options (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/StockBasedCompensationReconciliationofOutstandingStockOptionsDetails</Role>
      <ShortName>Stock-Based Compensation - Reconciliation of Outstanding Stock Options (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>2465440 - Disclosure - Stock-Based Compensation - Reconciliation of Nonvested Restricted Share and Share Unit Awards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/StockBasedCompensationReconciliationofNonvestedRestrictedShareandShareUnitAwardsDetails</Role>
      <ShortName>Stock-Based Compensation - Reconciliation of Nonvested Restricted Share and Share Unit Awards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>2466441 - Disclosure - Stock-Based Compensation - Weighted Average Fair Value of Options Granted and Black-Scholes Option Valuation Model Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/StockBasedCompensationWeightedAverageFairValueofOptionsGrantedandBlackScholesOptionValuationModelAssumptionsDetails</Role>
      <ShortName>Stock-Based Compensation - Weighted Average Fair Value of Options Granted and Black-Scholes Option Valuation Model Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>2469442 - Disclosure - Other Comprehensive Income (Loss) - Schedule of Components of Comprehensive Income (Loss) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/OtherComprehensiveIncomeLossScheduleofComponentsofComprehensiveIncomeLossDetails</Role>
      <ShortName>Other Comprehensive Income (Loss) - Schedule of Components of Comprehensive Income (Loss) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/OtherComprehensiveIncomeLossTables</ParentRole>
      <Position>89</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>2470443 - Disclosure - Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/OtherComprehensiveIncomeLossScheduleofAccumulatedOtherComprehensiveIncomeLossDetails</Role>
      <ShortName>Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/OtherComprehensiveIncomeLossTables</ParentRole>
      <Position>90</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>2471444 - Disclosure - Other Comprehensive Income (Loss) - Reclassification out of Accumulated Other Comprehensive Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/OtherComprehensiveIncomeLossReclassificationoutofAccumulatedOtherComprehensiveIncomeDetails</Role>
      <ShortName>Other Comprehensive Income (Loss) - Reclassification out of Accumulated Other Comprehensive Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/OtherComprehensiveIncomeLossTables</ParentRole>
      <Position>91</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>2474445 - Disclosure - Income Taxes - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/IncomeTaxesNarrativeDetails</Role>
      <ShortName>Income Taxes - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>92</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>2475446 - Disclosure - Income Taxes - Federal, State, and Foreign Income Tax (Benefit) Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/IncomeTaxesFederalStateandForeignIncomeTaxBenefitExpenseDetails</Role>
      <ShortName>Income Taxes - Federal, State, and Foreign Income Tax (Benefit) Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>93</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>2476447 - Disclosure - Income Taxes - Effective Income Tax Reconciliation and Provision for Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/IncomeTaxesEffectiveIncomeTaxReconciliationandProvisionforIncomeTaxesDetails</Role>
      <ShortName>Income Taxes - Effective Income Tax Reconciliation and Provision for Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>94</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>2477448 - Disclosure - Income Taxes - Deferred Tax Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/IncomeTaxesDeferredTaxAssetsandLiabilitiesDetails</Role>
      <ShortName>Income Taxes - Deferred Tax Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>95</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>2478449 - Disclosure - Income Taxes - Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/IncomeTaxesReconciliationoftheBeginningandEndingAmountofUnrecognizedTaxBenefitsDetails</Role>
      <ShortName>Income Taxes - Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>96</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>2481450 - Disclosure - Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/EarningsPerShareComputationofBasicandDilutedEarningsPerShareDetails</Role>
      <ShortName>Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>2482451 - Disclosure - Earnings Per Share - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/EarningsPerShareNarrativeDetails</Role>
      <ShortName>Earnings Per Share - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>98</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>2485452 - Disclosure - Segment Information - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SegmentInformationNarrativeDetails</Role>
      <ShortName>Segment Information - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R100.htm</HtmlFileName>
      <LongName>2486453 - Disclosure - Segment Information - (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SegmentInformationDetails</Role>
      <ShortName>Segment Information - (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/SegmentInformationTables</ParentRole>
      <Position>100</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R101.htm</HtmlFileName>
      <LongName>2487454 - Disclosure - Segment Information - Revenues and Long-lived Assets by Geographical Area (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SegmentInformationRevenuesandLonglivedAssetsbyGeographicalAreaDetails</Role>
      <ShortName>Segment Information - Revenues and Long-lived Assets by Geographical Area (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>101</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R102.htm</HtmlFileName>
      <LongName>2490455 - Disclosure - Selected Quarterly Financial Data (Unaudited) - Quarterly Financial Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SelectedQuarterlyFinancialDataUnauditedQuarterlyFinancialInformationDetails</Role>
      <ShortName>Selected Quarterly Financial Data (Unaudited) - Quarterly Financial Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/SelectedQuarterlyFinancialDataUnauditedTables</ParentRole>
      <Position>102</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>2491456 - Disclosure - Selected Quarterly Financial Data - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SelectedQuarterlyFinancialDataNarrativeDetails</Role>
      <ShortName>Selected Quarterly Financial Data - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>103</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>2494457 - Disclosure - Related Party Transactions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/RelatedPartyTransactionsDetails</Role>
      <ShortName>Related Party Transactions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/RelatedPartyTransactions</ParentRole>
      <Position>104</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R105.htm</HtmlFileName>
      <LongName>2496458 - Disclosure - Subsequent Events (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/SubsequentEventsDetails</Role>
      <ShortName>Subsequent Events (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/SubsequentEvents</ParentRole>
      <Position>105</Position>
    </Report>
    <Report instance="lfus-20201226.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R106.htm</HtmlFileName>
      <LongName>2498459 - Disclosure - Schedule II - Valuation and Qualifying Accounts and Reserves (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.littelfuse.com/role/ScheduleIIValuationandQualifyingAccountsandReservesDetails</Role>
      <ShortName>Schedule II - Valuation and Qualifying Accounts and Reserves (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.littelfuse.com/role/ScheduleIIValuationandQualifyingAccountsandReserves</ParentRole>
      <Position>106</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-K" original="lfus-20201226.htm">lfus-20201226.htm</File>
    <File>exhibit1068-firstamendment.htm</File>
    <File>exhibit1069-secondamendmen.htm</File>
    <File>exhibit1070-thirdamendment.htm</File>
    <File>exhibit1071-tierichangeofc.htm</File>
    <File>exhibit1072-tieriichangeof.htm</File>
    <File>exhibit1073-directorcompen.htm</File>
    <File>exhibit211-12262010k.htm</File>
    <File>exhibit231-12262010k.htm</File>
    <File>exhibit311-12262010k.htm</File>
    <File>exhibit312-12262010k.htm</File>
    <File>exhibit321-12262010k.htm</File>
    <File>lfus-20201226.xsd</File>
    <File>lfus-20201226_cal.xml</File>
    <File>lfus-20201226_def.xml</File>
    <File>lfus-20201226_lab.xml</File>
    <File>lfus-20201226_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>lfus-20201226_g1.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/country/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2020-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
