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Fair Value Measurements - Investment Impairments and Credit Loss Reserves (Details) - USD ($) $ in Thousands | 6 Months Ended |
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Jul. 26, 2020 | Jan. 27, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Increase in credit loss reserves on available-for-sale securities | $ 2,389 |
Credit loss reserve for available-for-sale and held-to-maturity debt securities | (2,900) |
Impairment on non-marketable equity securities | $ 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

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