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Income Taxes (Details) (USD $)
3 Months Ended
Apr. 04, 2015
Mar. 29, 2014
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]    
Income tax expense $ 24,665,000us-gaap_IncomeTaxExpenseBenefit $ 1,727,000us-gaap_IncomeTaxExpenseBenefit
Income Tax Examination, Estimate of Possible Loss 14,100,000us-gaap_IncomeTaxExaminationEstimateOfPossibleLoss  
Unrecognized Tax Benefits, Remaining, not subject to examination, lapse of applicable statute of limitations 1,100,000lscc_UnrecognizedTaxBenefitsRemainingNotSubjecttoExaminationLapseofApplicableStatuteofLimitations  
Lapse of the statute of limitations on foreign tax filings    
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]    
Unrecognized tax benefits that could significantly change during the next twelve months 15,200,000us-gaap_UnrecognizedTaxBenefits
/ us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis
= lscc_LapseOfStatuteOfLimitationsMember
 
Total potential decrease in UTB 15,200,000us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleEstimatedRangeOfChangeUpperBound
/ us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis
= lscc_LapseOfStatuteOfLimitationsMember
 
Maximum | Lapse of the statute of limitations on foreign tax filings    
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]    
Unrecognized tax benefits, associated interest and penalties that could significantly change within the next twelve months $ 100,000us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis
= lscc_LapseOfStatuteOfLimitationsMember
 
U.S. Federal    
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]    
Statutory income tax rate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_DomesticCountryMember