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Income Taxes (Discussion of Unrecognized Tax Benefits) (Details) (USD $)
12 Months Ended
Jan. 03, 2015
Dec. 28, 2013
Dec. 29, 2012
Income Tax Contingency [Line Items]      
Undistributed earnings of our Chinese subsidiary $ 3,300,000us-gaap_UndistributedEarningsOfForeignSubsidiaries    
Unrecognized tax benefits associated with uncertain tax positions 18,673,000us-gaap_UnrecognizedTaxBenefits 22,643,000us-gaap_UnrecognizedTaxBenefits 21,680,000us-gaap_UnrecognizedTaxBenefits
Unrecognized tax benefits associated with uncertain tax positions that, if recognized, would affect the effective tax rate 17,400,000us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate    
Interest and penalties associated with unrecognized tax benefits 200,000us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued    
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]      
Beginning balance 22,643,000us-gaap_UnrecognizedTaxBenefits 21,680,000us-gaap_UnrecognizedTaxBenefits 21,552,000us-gaap_UnrecognizedTaxBenefits
Additions based on tax positions related to the current year 770,000us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions 1,600,000us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions 384,000us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions
Additions based on tax positions of prior years 0us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions 68,000us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions 192,000us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions
Reduction for tax positions of prior years (4,673,000)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions 0us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions (26,000)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions
Settlements 0us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities (338,000)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities (30,000)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities
Reduction as a result of lapse of applicable statute of limitations (67,000)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations (367,000)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations (392,000)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations
Ending balance 18,673,000us-gaap_UnrecognizedTaxBenefits 22,643,000us-gaap_UnrecognizedTaxBenefits 21,680,000us-gaap_UnrecognizedTaxBenefits
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 67,000lscc_UnrecognizedTaxBenefitsRemainingNotSubjecttoExaminationLapseofApplicableStatuteofLimitations    
Expiration of statutes of limitations | Foreign tax filings      
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]      
Amount of unrecognized tax benefits that could significantly change during the next twelve months 14,200,000us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleAmountOfUnrecordedBenefit
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_ForeignCountryMember
/ us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis
= lscc_LapseOfStatuteOfLimitationsMember
   
Expiration of statutes of limitations | Foreign tax filings | Maximum      
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]      
Amount of associated interest and penalties that could significantly change within the next twelve months $ 100,000lscc_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleAmountOfAssociatedIncomeTaxPenaltiesAndInterestAccrued
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_ForeignCountryMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis
= lscc_LapseOfStatuteOfLimitationsMember