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FAIR VALUE MEASUREMENTS - Non-recurring Basis (Details) - USD ($)
$ in Thousands
Apr. 30, 2019
Jul. 31, 2018
Jul. 31, 2017
Convertible Debt      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Unamortized discount $ (117,070) $ (137,719)  
Unamortized debt issuance cost $ (6,531) (7,683)  
Reported Value Measurement | Fair Value, Measurements, Nonrecurring      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Convertible senior notes, net   451,399 $ 429,598
Estimate of Fair Value Measurement | Fair Value, Measurements, Nonrecurring      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Convertible senior notes, net   $ 657,921 $ 685,527