Credit Facilities Narrative (Details) (USD $)	3 Months Ended		0 Months Ended			3 Months Ended	12 Months Ended
	Apr. 26, 2015	Apr. 27, 2014	May 02, 2013	Jun. 03, 2013	Jul. 14, 2014	Jul. 28, 2013	Jan. 26, 2014	Mar. 20, 2012
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
Original issue discount on debt								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
Original issue discount on debt								2,500,000
New credit facilities, Term Loan [Member]
New credit facilities, maximum borrowing capacity			150,000,000
New credit facilities, amount outstanding	91,200,000		149,300,000
New credit facilities, Interest rate at period end	1.93%
Principal payments remaining in fiscal year 2016	14,100,000
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	193,000,000		177,300,000
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]
Original issue discount on debt			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