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Fair Value Measurements Narrative (Details) - USD ($)
$ / shares in Units, $ in Thousands
Jan. 31, 2020
Oct. 31, 2019
Debt Instrument [Line Items]    
Closing price of common stock (in dollars per share) $ 128.05  
Convertible Senior Notes Due 2023 | Senior Notes    
Debt Instrument [Line Items]    
Aggregate principal amount $ 120,588 $ 345,000