Income Taxes - Narrative (Details) $ in Thousands, SFr in Millions			3 Months Ended		12 Months Ended
	May 19, 2019	Dec. 06, 2016 CHF (SFr)	Jan. 31, 2021 USD ($)	Apr. 26, 2020 USD ($)	Jan. 31, 2021 USD ($)	Jan. 26, 2020 USD ($)	Jan. 27, 2019 USD ($)	Jan. 28, 2018 USD ($)
Income Tax [Line Items]
GILTI effective tax rate					10.50%
Reduction of valuation allowance				$ 15,800	$ 438	$ 2,722	$ 23,029
Provisional income tax expense due to mandatory transition tax on the deemed repatriation of undistributed foreign earnings					2,100
Tax attributes used to completely offset any cash tax liability resulting from the transition tax					76,500
Increase to tax provision expense			$ 1,900
Foreign earnings that will continue to be reinvested indefinitely outside of the U.S.			547,900		547,900
Foreign earnings that will be remitted in the foreseeable future					240,000
Foreign earnings remitted			83,900		83,900	76,100	80,000
Deferred tax asset recognized for windfall tax benefits			1,300		1,300
Gross research credits available to offset taxable income			9,700		9,700	6,063
Net deferred tax assets			40,300		40,300	32,700
Valuation allowance			15,751		$ 15,751	16,189	$ 18,912	$ 41,050
Valuation allowance, methodologies and assumptions					The valuation allowances established relate to all U. S. and state deferred tax assets, for which we have determined that it is more likely than not that a benefit will not be realized. In considering in whether a valuation allowance was required for our U.S. deferred income tax assets, we considered all available positive and negative evidence. Positive evidence considered included reversing taxable temporary differences. Negative evidence considered included the cumulative taxable losses in the U.S. recorded during the three year period ended January 29, 2018, on both an annual and cumulative basis. Based on the weight of all available evidence, we concluded that the negative evidence outweighed the positive evidence and that it was more likely than not that the U.S. federal and state deferred tax assets that cannot be realized through the reversal of taxable temporary differences would not be realized. As a result, we have established a full valuation allowance against the deferred tax assets in the U.S. that will not be realized through the reversal of taxable temporary differences.
Percentage of uncertain tax positions evaluating criteria					50.00%
Net tax benefits, if recognized, would impact the effective tax rate			9,700		$ 9,700	8,600
Unrecognized tax benefits, interest and penalties			1,000		1,000	$ 0
Deferred Tax Liabilities, Undistributed Foreign Earnings			50,000		$ 50,000
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
Gross research credits available to offset taxable income			3,700		$ 3,700
Foreign | Swiss Federal Tax Administration (FTA)
Income Tax [Line Items]
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	2.54%
Income Tax, Statutory Cantonial Tax Rate	0.0846
Federal
Income Tax [Line Items]
Gross research credits available to offset taxable income			11,200		11,200
State
Income Tax [Line Items]
Operating loss carryforwards			104,400		104,400
Gross research credits available to offset taxable income			$ 15,400		$ 15,400
Maximum | Foreign
Income Tax [Line Items]
Potential tax savings | SFr		SFr 44.0