Credit Facilities - Narrative (Details)				3 Months Ended	6 Months Ended		12 Months Ended
	Jul. 14, 2014 USD ($)	Jun. 03, 2013 USD ($)	May. 02, 2013 USD ($)	Jul. 28, 2013 USD ($)	Jul. 26, 2015 USD ($)	Jul. 27, 2014 USD ($)	Jan. 26, 2014 USD ($)	Mar. 20, 2012 USD ($)
Prior credit facilities, aggregate principal amount of term loans								$ 350,000,000
New credit facilities, maximum borrowing capacity			$ 400,000,000
New credit facilities, amount outstanding			326,600,000
Prior credit facilities, repayment of outstanding obligations			$ 327,500,000
Borrowings under line of credit					$ 35,000,000	$ 0
Minimum [Member]
Interest coverage ratio					3.50
Maximum [Member]
Total leverage ratio					3.00
Base Rate [Member]
Description of variable rate basis			the highest of (a) the prime rate (as published by The Wall Street Journal), (b) ½ of 1% above the federal funds effective rate or (c) one-month LIBOR (determined with respect to deposits in U.S. Dollars) plus 1%.
Base Rate [Member] | Minimum [Member]
Basis spread on variable rate			0.25%
Base Rate [Member] | Maximum [Member]
Basis spread on variable rate			1.25%
LIBOR [Member]
Basis spread on variable rate			1.00%
LIBOR [Member] | Minimum [Member]
Basis spread on variable rate			1.25%
LIBOR [Member] | Maximum [Member]
Basis spread on variable rate			2.25%
Federal Funds [Member]
Basis spread on variable rate			1.00%
CDOR [Member]
Description of variable rate basis			the sum of: (a) the rate determined by Administrative Agent with reference to the arithmetic average of the discount rate quotations of all institutions listed for CAD Dollar-denominated bankers’ acceptances displayed and identified on the “Reuters Screen CDOR Page” and (b) 0.10% per annum
Basis spread on variable rate			0.10%
CDOR [Member] | Minimum [Member]
Basis spread on variable rate			1.25%
CDOR [Member] | Maximum [Member]
Basis spread on variable rate			2.25%
Prior credit facilities, Term A Loans [Member]
Prior credit facilities, aggregate principal amount of term loans								100,000,000
Initial carrying amounts								99,500,000
Debt discounts, net book value								500,000
Prior credit facilities, Term B Loans [Member]
Prior credit facilities, aggregate principal amount of term loans								250,000,000
Initial carrying amounts								247,500,000
Debt discounts, net book value								$ 2,500,000
New credit facilities, Term Loan [Member]
New credit facilities, maximum borrowing capacity			$ 150,000,000
New credit facilities, amount outstanding			149,300,000		$ 86,500,000
New credit facilities, Interest rate at period end					1.93%
Principal payments remaining in fiscal year 2016					$ 9,400,000
Principal payments in fiscal year 2017					18,800,000
Principal payments in fiscal year 2018					24,400,000
Repayments of debt		$ 26,000,000
New credit facilities, Revolving Credit Facility [Member]
New credit facilities, maximum borrowing capacity			250,000,000
New credit facilities, amount outstanding			$ 177,300,000		$ 193,000,000
New credit facilities, Interest rate at period end					1.93%
Repayments of debt	$ 25,000,000
New credit facilities, Revolving Credit Facility [Member] | Minimum [Member]
New credit facilities, unused capacity, commitment fee percentage			0.20%
New credit facilities, Revolving Credit Facility [Member] | Maximum [Member]
New credit facilities, unused capacity, commitment fee percentage			0.45%
New credit facilities [Member]
Debt discounts, net book value			$ 1,400,000	$ 600,000
New credit facilities, debt discount expensed				800,000
New credit facilities, deferred financing cost				2,200,000
New credit facilities, deferred financing costs expensed				1,000,000
Deferred finance costs capitalized				$ 1,200,000
New credit facilities, contractual term			5 years
Prior credit facilities [Member]
Deferred finance costs capitalized			$ 1,700,000
Prior credit facilities, loss on modification of debt							$ 7,100,000
New credit facilities, Letter of Credit [Member]
New credit facilities, maximum borrowing capacity			40,000,000
New credit facilities, amount outstanding					$ 0
New credit facilities, Swingline Loans [Member]
New credit facilities, maximum borrowing capacity			25,000,000
New credit facilities, amount outstanding					0
New credit facilities, Revolving Loans and Non US Dollars LC [Member]
New credit facilities, maximum borrowing capacity			40,000,000
New credit facilities, amount outstanding					0
Additional Term Loan or Increase in Revolver [Member]
New credit facilities, maximum borrowing capacity			$ 100,000,000
Alternative Currencies, Except Canadian [Member]
Description of variable rate basis			a rate per annum equal to LIBOR (determined with respect to deposits in the applicable Alternative Currency) for an interest period to be selected by Semtech plus a margin ranging from 1.25% to 2.25% depending upon Semtech’s consolidated leverage ratio.
United States of America, Dollars
Description of variable rate basis			(1) the Base Rate plus a margin ranging from 0.25% to 1.25% depending upon Semtech’s consolidated leverage ratio or (2) LIBOR (determined with respect to deposits in U.S. Dollars) for an interest period to be selected by Semtech plus a margin ranging from 1.25% to 2.25% depending upon Semtech’s consolidated leverage ratio.
Canada, Dollars
Description of variable rate basis			a rate per annum equal to the CDOR Rate for an interest period to be selected by Semtech plus a margin ranging from 1.25% to 2.25% depending upon Semtech’s consolidated leverage ratio.
Through second quarter of fiscal year 2018 [Domain]
New credit facilities, required quarterly principal payment					4,700,000
Beginning third quarter of fiscal year 2018 [Domain]
New credit facilities, required quarterly principal payment					$ 7,500,000