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Note 1 - Summary of Significant Accounting Policies and Other Information (Details) (USD $)
 12 Months Ended
Dec. 27, 2014
Dec. 28, 2013
Dec. 29, 2012
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Number of Reportable Segments 8us-gaap_NumberOfReportableSegments    
Goodwill, Impairment Loss (in Dollars) $ 0us-gaap_GoodwillImpairmentLoss    
Sensitivity Analysis, Increase In Discount Rate 100.00%lfus_SensitivityAnalysisIncreaseInDiscountRate    
Sensitivity Analysis, Decrease In Long-term Growth Rate 100.00%lfus_SensitivityAnalysisDecreaseInLongtermGrowthRate    
Finite-Lived Intangible Asset, Useful Life 12 years 6 months 11 years 292 days  
Defined Benefit Plan, Purchases, Sales, and Settlements (in Dollars)     5,100,000us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
Advertising Expense (in Dollars) 2,800,000us-gaap_AdvertisingExpense 1,600,000us-gaap_AdvertisingExpense 1,700,000us-gaap_AdvertisingExpense
Shipping, Handling and Transportation Costs (in Dollars) 6,700,000us-gaap_ShippingHandlingAndTransportationCosts 6,500,000us-gaap_ShippingHandlingAndTransportationCosts 6,200,000us-gaap_ShippingHandlingAndTransportationCosts
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax (in Dollars) (4,600,000)us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax 5,200,000us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax (8,500,000)us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax
Other Nonoperating Income (Expense) (in Dollars) $ 6,644,000us-gaap_OtherNonoperatingIncomeExpense $ 4,646,000us-gaap_OtherNonoperatingIncomeExpense $ 5,396,000us-gaap_OtherNonoperatingIncomeExpense
Building [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Property, Plant and Equipment, Useful Life 21 years    
Equipment [Member] | Minimum [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Property, Plant and Equipment, Useful Life 7 years    
Equipment [Member] | Maximum [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Property, Plant and Equipment, Useful Life 9 years    
Furniture and Fixtures [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Property, Plant and Equipment, Useful Life 7 years    
Tooling [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Property, Plant and Equipment, Useful Life 5 years    
Computer Equipment [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Property, Plant and Equipment, Useful Life 3 years    
Electronics Non Silicon Unit [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Excess of Fair Value Over Carrying Value of Invested Capital (as a percent) 114.00%lfus_ExcessOfFairValueOverCarryingValueOfInvestedCapital
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_ElectronicsNonSiliconUnitMember		    
Electronics Silicon Unit [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Excess of Fair Value Over Carrying Value of Invested Capital (as a percent) 128.00%lfus_ExcessOfFairValueOverCarryingValueOfInvestedCapital
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_ElectronicsSiliconUnitMember		    
Passenger Car [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Excess of Fair Value Over Carrying Value of Invested Capital (as a percent) 128.00%lfus_ExcessOfFairValueOverCarryingValueOfInvestedCapital
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_PassengerCarMember		    
Commercial Vehicle Products [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Excess of Fair Value Over Carrying Value of Invested Capital (as a percent) 190.00%lfus_ExcessOfFairValueOverCarryingValueOfInvestedCapital
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_CommercialVehicleProductsMember		    
Sensors [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Excess of Fair Value Over Carrying Value of Invested Capital (as a percent) 26.00%lfus_ExcessOfFairValueOverCarryingValueOfInvestedCapital
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_SensorsMember		    
Relay Unit [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Excess of Fair Value Over Carrying Value of Invested Capital (as a percent) 6.00%lfus_ExcessOfFairValueOverCarryingValueOfInvestedCapital
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_RelayUnitMember		    
Fair Value Inputs, Discount Rate 12.80%us-gaap_FairValueInputsDiscountRate
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_RelayUnitMember		    
Fair Value Inputs, Control Premium 1.00%us-gaap_FairValueInputsControlPremium
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_RelayUnitMember		    
Custom Products Unit [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Excess of Fair Value Over Carrying Value of Invested Capital (as a percent) 82.00%lfus_ExcessOfFairValueOverCarryingValueOfInvestedCapital
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_CustomProductsUnitMember		    
Fuse Unit [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Excess of Fair Value Over Carrying Value of Invested Capital (as a percent) 83.00%lfus_ExcessOfFairValueOverCarryingValueOfInvestedCapital
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_FuseUnitMember		    
All Reporting Units Other Than Relay Unit [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Fair Value Inputs, Discount Rate 11.80%us-gaap_FairValueInputsDiscountRate
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_AllReportingUnitsOtherThanRelayUnitMember		    
Fair Value Inputs, Long-term Revenue Growth Rate 3.00%us-gaap_FairValueInputsLongTermRevenueGrowthRate
/ us-gaap_StatementBusinessSegmentsAxis
= lfus_AllReportingUnitsOtherThanRelayUnitMember		    
Trademarks and Trade Names [Member] | Minimum [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Finite-Lived Intangible Asset, Useful Life 5 years    
Trademarks and Trade Names [Member] | Maximum [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Finite-Lived Intangible Asset, Useful Life 20 years    
Patents Licenses And Software [Member] | Minimum [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Finite-Lived Intangible Asset, Useful Life 7 years    
Patents Licenses And Software [Member] | Maximum [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Finite-Lived Intangible Asset, Useful Life 12 years    
Patents Licenses And Software [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Finite-Lived Intangible Asset, Useful Life 11 years 255 days [1] 11 years [1]  
Distribution Rights [Member] | Minimum [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Finite-Lived Intangible Asset, Useful Life 3 years    
Distribution Rights [Member] | Maximum [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Finite-Lived Intangible Asset, Useful Life 20 years    
Distribution Rights [Member]      
Note 1 - Summary of Significant Accounting Policies and Other Information (Details) [Line Items]      
Finite-Lived Intangible Asset, Useful Life 12 years 146 days [1] 12 years 109 days [1]  
[1] Increase to gross carrying value in 2014 is primarily related to the preliminary SymCom acquisition purchase price allocation discussed in Note 2. Other changes are primarily due to the impact of foreign currency translation adjustments.