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Debt - Convertible Senior Notes Due 2021 (Details)
3 Months Ended 6 Months Ended
Sep. 15, 2015
USD ($)
$ / shares
Jul. 27, 2019
USD ($)
Jul. 28, 2018
USD ($)
Oct. 24, 2015
trading_day
Jul. 27, 2019
USD ($)
Jul. 28, 2018
USD ($)
Jan. 26, 2019
USD ($)
Debt Instrument [Line Items]              
Amortization of debt discount         $ 9,947,000 $ 9,422,000  
0.75% Convertible Senior Notes Due 2021              
Debt Instrument [Line Items]              
Debt, interest rate (in percent)   0.75%     0.75%    
Debt intrument, conversion installments amount $ 1,000            
Debt instrument,conversion ratio 10.3211            
Debt instrument, face amount $ 485,000,000.0 $ 485,000,000     $ 485,000,000   $ 485,000,000
Debt instrument, convertible, conversion price (per share) | $ / shares $ 96.89            
Convertible debt, trading day threshold | trading_day       20      
Convertible debt, consecutive trading day threshold | trading_day       30      
Convertible debt, percentage of stock trigger price threshold       130.00%      
Debt instrument conversion trigger price | $ / shares $ 125.96            
Convertible debt, measurement period for percentage of product sale price of common stock and applicable conversion threshold       98.00%      
Convertible debt, comparable yield   5.50%          
Amortization of debt discount   $ 5,000,000.0 $ 4,800,000   9,900,000 $ 9,400,000  
Convertible Debt   434,152,000     434,152,000   423,199,000
Unamortized discount   45,848,000     45,848,000   55,795,000
Debt issuance cost   5,000,000     5,000,000   6,006,000
Standby Letters of Credit              
Debt Instrument [Line Items]              
Line of credit   $ 0     $ 0   $ 0