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Fair Value of Financial Instruments (Details) (USD $)
3 Months Ended
Apr. 04, 2015
Mar. 29, 2014
Jun. 28, 2014
Jan. 03, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Fair value of marketable securities $ 40,127,000us-gaap_AvailableForSaleSecurities     $ 139,233,000us-gaap_AvailableForSaleSecurities
Total        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Foreign currency forward exchange contracts, net 339,000us-gaap_ForeignCurrencyContractAssetFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
    414,000us-gaap_ForeignCurrencyContractAssetFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Total fair value of financial instruments 40,466,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
    139,647,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Short-term marketable securities        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Fair value of marketable securities 40,127,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= lscc_ShortTermMember
    139,233,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= lscc_ShortTermMember
Short-term marketable securities | Total        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Fair value of marketable securities 40,127,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= lscc_ShortTermMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
    139,233,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= lscc_ShortTermMember
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Level 1        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Foreign currency forward exchange contracts, net 0us-gaap_ForeignCurrencyContractAssetFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
    0us-gaap_ForeignCurrencyContractAssetFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Total fair value of financial instruments 34,498,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
    139,233,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Level 1 | Short-term marketable securities        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Fair value of marketable securities 34,498,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= lscc_ShortTermMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
    139,233,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= lscc_ShortTermMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Level 2        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Foreign currency forward exchange contracts, net 339,000us-gaap_ForeignCurrencyContractAssetFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
    414,000us-gaap_ForeignCurrencyContractAssetFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Total fair value of financial instruments 5,968,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
    414,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Level 2 | Short-term marketable securities        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Fair value of marketable securities 5,629,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= lscc_ShortTermMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
    0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= lscc_ShortTermMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Level 3        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Foreign currency forward exchange contracts, net 0us-gaap_ForeignCurrencyContractAssetFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
    0us-gaap_ForeignCurrencyContractAssetFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Total fair value of financial instruments 0us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
    0us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
   
Level 3 | Short-term marketable securities        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Fair value of marketable securities 0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= lscc_ShortTermMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
    0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByAssetClassAxis
= lscc_ShortTermMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Federally-insured or FFELP guaranteed student loan auction rate securities        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Par value     5,700,000lscc_ParValueOfAvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= lscc_FederallyInsuredOrFfelpGuaranteedStudentLoanAuctionRateSecuritiesMember
 
Federally-insured or FFELP guaranteed student loan auction rate securities | Level 3        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales     $ 5,200,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= lscc_FederallyInsuredOrFfelpGuaranteedStudentLoanAuctionRateSecuritiesMember