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Fair Value Measurements Schedule of Carrying Amounts and Estimated Fair Values of Convertible Note (Details) - Senior Notes
$ in Thousands
Jan. 31, 2020
USD ($)
Net Carrying Amount | Convertible Senior Notes Due 2023  
Debt Instrument [Line Items]  
Convertible senior notes value $ 102,543
Net Carrying Amount | Convertible Senior Notes Due 2025  
Debt Instrument [Line Items]  
Convertible senior notes value 851,535
Estimated Fair Value | Convertible Senior Notes Due 2023  
Debt Instrument [Line Items]  
Convertible senior notes value 331,014
Estimated Fair Value | Convertible Senior Notes Due 2025  
Debt Instrument [Line Items]  
Convertible senior notes value $ 1,074,840