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CONVERTIBLE SENIOR NOTES - Components of Notes (Details) - USD ($)
$ in Thousands
Apr. 30, 2019
Jul. 31, 2018
Apr. 30, 2018
Debt Instrument [Line Items]      
Convertible senior notes, net $ 451,399 $ 429,598  
Convertible Debt      
Debt Instrument [Line Items]      
Principal amount 575,000 575,000 $ 575,000
Unamortized discount (117,070) (137,719)  
Unamortized debt issuance cost (6,531) (7,683)  
Carrying amount of the equity component $ 148,598 $ 148,598  
Effective interest rate 6.62%    
Payments of offering costs $ (3,000)   $ (3,000)