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Commitments and Contingencies - Narrative (Details) (USD $)
 12 Months Ended 0 Months Ended
Jan. 25, 2015
Jan. 26, 2014
Jan. 27, 2013
Dec. 17, 2014
Nov. 13, 2014
Jan. 23, 2013
Commitments And Contingencies [Line Items]            
Rent expense $ 8,800,000us-gaap_LeaseAndRentalExpense $ 9,300,000us-gaap_LeaseAndRentalExpense $ 7,900,000us-gaap_LeaseAndRentalExpense      
Sublease income 142,000us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue 140,000us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue 133,000us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue      
Purchase obligation 36,554,000us-gaap_PurchaseObligation          
Payments for Restructuring (3,520,000)us-gaap_PaymentsForRestructuring (454,000)us-gaap_PaymentsForRestructuring        
Employer contribution to defined benefit plan 900,000us-gaap_DefinedBenefitPlanContributionsByEmployer 800,000us-gaap_DefinedBenefitPlanContributionsByEmployer 800,000us-gaap_DefinedBenefitPlanContributionsByEmployer      
Maximum potential payment under earn-out arrangement 16,000,000smtc_EarnOutArrangementWithCyceloMaximumPotentialPayment          
Earn-out arrangement with Cycleo, earn-out liability 1,700,000smtc_EarnoutArrangementwithCycleoEarnoutLiability          
Convertible Preferred Stock            
Commitments And Contingencies [Line Items]            
Purchase obligation 1,400,000us-gaap_PurchaseObligation
/ smtc_PurchaseCommitmentTypeAxis
= us-gaap_ConvertiblePreferredStockMember		          
Other assets            
Commitments And Contingencies [Line Items]            
Cash surrender value of life insurance 18,500,000us-gaap_CashSurrenderValueOfLifeInsurance
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherAssetsMember		 14,400,000us-gaap_CashSurrenderValueOfLifeInsurance
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherAssetsMember		        
Environmental Issue [Member]            
Commitments And Contingencies [Line Items]            
Lease duration 40 years          
Range of possible loss, minimum 2,700,000us-gaap_LossContingencyRangeOfPossibleLossMinimum
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_EnvironmentalIssueMember		          
Range of possible loss, maximum 5,700,000us-gaap_LossContingencyRangeOfPossibleLossMaximum
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_EnvironmentalIssueMember		          
Environmental Issue [Member] | Other long-term liabilities            
Commitments And Contingencies [Line Items]            
Loss contingency accrual 2,700,000us-gaap_LossContingencyAccrualAtCarryingValue
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherNoncurrentLiabilitiesMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_EnvironmentalIssueMember		          
Commercial Dispute [Member]            
Commitments And Contingencies [Line Items]            
Loss contingency, name of plaintiff       Semtech Intrigo Systems, Inc. Intrigo Systems, Inc.
Loss contingency, damages sought by plaintiff       3,700,000us-gaap_LossContingencyDamagesSoughtValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= smtc_CommercialDisputeMember		 2,700,000us-gaap_LossContingencyDamagesSoughtValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= smtc_CommercialDisputeMember		 2,600,000us-gaap_LossContingencyDamagesSoughtValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= smtc_CommercialDisputeMember
One-time employee termination benefits            
Commitments And Contingencies [Line Items]            
Payments for Restructuring 1,767,000us-gaap_PaymentsForRestructuring
/ us-gaap_RestructuringCostAndReserveAxis
= us-gaap_OneTimeTerminationBenefitsMember		 454,000us-gaap_PaymentsForRestructuring
/ us-gaap_RestructuringCostAndReserveAxis
= us-gaap_OneTimeTerminationBenefitsMember		        
United States Postretirement Benefit Plan of US Entity [Member]            
Commitments And Contingencies [Line Items]            
Employer contribution to defined contribution plan 1,300,000us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanTypeAxis
= us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember		 1,400,000us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanTypeAxis
= us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember		 1,200,000us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanTypeAxis
= us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember		      
Foreign Postretirement Benefit Plan [Member]            
Commitments And Contingencies [Line Items]            
Employer contribution to defined contribution plan $ 1,300,000us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanTypeAxis
= us-gaap_ForeignPostretirementBenefitPlansDefinedBenefitMember