Fair Value Measurements - Investment Impairments and Credit Loss Reserves (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 25, 2020	Apr. 26, 2020	Oct. 25, 2020	Jan. 27, 2020	Jan. 26, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting standards update		us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Increase in credit loss reserves on available-for-sale and held-to-maturity debt securities	$ 300		$ 2,719
Credit loss reserve for available-for-sale and held-to-maturity debt securities	3,200		3,200
Impairment on non-marketable equity securities	$ 0		$ 2,900
ASU 2016-13 | Cumulative Effect, Period Of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Credit loss reserve on held-to-maturity securities				$ 400	$ 400