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Stock-Based Compensation - Fair value options (Details) - 2016 Equity Plan - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Jan. 25, 2020
Jan. 26, 2019
Jan. 27, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date fair value of options $ 1.3 $ 52.4 $ 12.2
Intrinsic fair value of options exercised $ 3.4 $ 51.3 $ 20.8
Weighted-average fair value of options granted (in dollars per share) $ 6.87 $ 19.03 $ 10.38