Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	Dec. 17, 2014	Nov. 13, 2014	Jan. 23, 2013	Jul. 26, 2015	Mar. 04, 2015	Jan. 25, 2015
Cycleo [Member]
Loss Contingencies [Line Items]
Potential payments under earn-out arrangements, high estimate				$ 16.0
Earn-out liability booked				3.9		$ 1.7
Environmental Issue
Loss Contingencies [Line Items]
Range of possible loss, minimum				5.3		2.7
Range of possible loss, maximum				7.5		$ 5.7
Environmental loss contingency accrual, at carrying value				5.3
Commercial Dispute
Loss Contingencies [Line Items]
Name of plaintiff	Semtech	Intrigo	Intrigo
Loss contingency, damages sought	$ 3.7	$ 2.7	$ 2.6
Earn-out Payable Within First Three Fiscal Years Of Acquisition Date [Member] | Triune Systems [Member]
Loss Contingencies [Line Items]
Potential payments under earn-out arrangements, high estimate					$ 70.0
Additional Earn-out Payable After Third Fiscal Year From Acquisition Date [Member] | Triune Systems [Member]
Loss Contingencies [Line Items]
Potential payments under earn-out arrangements, high estimate					$ 16.0
Other liabilities [Member] | Triune Systems [Member]
Loss Contingencies [Line Items]
Earn-out liability booked				$ 16.9