Income Taxes - Narrative (Details) $ in Thousands, SFr in Millions		12 Months Ended
	Dec. 06, 2016 CHF (SFr)	Jan. 29, 2017 USD ($)	Jan. 31, 2016 USD ($)	Jan. 25, 2015 USD ($)	Jan. 26, 2014 USD ($)
Income Tax [Line Items]
Net operating loss carryforward deferred tax asset attributed to excess equity deductions		$ 8,400
Canadian research credits available to offset taxable income		25,770	$ 32,605
Unremitted earnings related to foreign subsidiaries		$ 603,000
Percentage of uncertain tax positions evaluating criteria		50.00%
Net tax benefits, if recognized, would impact the effective tax rate		$ 9,300	8,400
Unrecognized tax benefits, interest and penalties		300	300
Valuation allowance		82,961	77,383	$ 75,536	$ 61,251
Charge to income tax provision as a result of increase in valuation allowance		$ 5,578	1,847	14,284
Valuation allowance, methodologies and assumptions		The Company assessed whether a valuation allowance should be recorded against all of its deferred tax assets (“DTAs”) based on the consideration of all available evidence, using a “more likely than not” realization standard. The four sources of taxable income that must be considered in determining whether DTAs will be realized are, (1) future reversals of existing taxable temporary differences (i.e., offset of gross deferred tax assets against gross deferred tax liabilities); (2) taxable income in prior carryback years, if carryback is permitted under the tax law; (3) tax planning strategies and (4) future taxable income exclusive of reversing temporary differences and carryforwards. In assessing whether a valuation allowance is required, significant weight is to be given to evidence that can be objectively verified. The Company evaluated its DTAs each reporting period, including an assessment of the cumulative income or loss over the most recent three-year period, to determine if a valuation allowance was required. A significant negative factor in the assessment was the Company’s three-year cumulative loss history as of January 25, 2015 and January 26, 2014 in Canada and the U.S. After a review of the four sources of taxable income described above and in view of its three-year cumulative losses, the Company was not able to conclude that it is more likely than not that its DTAs in Canada and the U.S. at January 25, 2015 and January 26, 2014 will be realized.
Benefit to income tax provision from release of valuation allowance on Canadian deferred tax asset		$ 0	$ 7,208	$ 0
Foreign
Income Tax [Line Items]
Description of income tax holiday		On December 6, 2016, the Company was granted a tax holiday ("Tax Holiday") with an effective date of January 30, 2017. This Tax Holiday replaces the current Swiss Ruling. The Tax Holiday provides Semtech (International) AG with a 70% reduction to the Cantonal tax rate, bringing the statutory Cantonal tax rate down from 12.56% to 3.77%. The maximum benefit under this Tax Holiday is CHF 500.0 million of cumulative after tax profit which equates to a maximum potential tax savings of CHF 44.0 million. The Tax Holiday is effective for five years and can be extended for an additional five years if the Company meets certain staffing targets by January 30, 2022.
Reduction in statutory Cantonal tax rate, percentage	70.00%
Statutory Cantonal tax rate before tax holiday, percentage	12.56%
Statutory Cantonal tax rate after tax holiday, percentage	3.77%
Maximum after-tax profit subject to potential savings | SFr	SFr 500.0
Income tax holiday, initial term	5 years
Income tax holiday, possible additional term	5 years
Canadian research credits available to offset taxable income		$ 17,800
Federal
Income Tax [Line Items]
Operating loss carryforwards		126,700
Canadian research credits available to offset taxable income		13,400
Alternative minimum tax credits available		1,300
State
Income Tax [Line Items]
Operating loss carryforwards		91,100
Canadian research credits available to offset taxable income		$ 14,500
Maximum | Foreign
Income Tax [Line Items]
Potential tax savings | SFr	SFr 44.0