Convertible Senior Notes - Schedule of Carrying Amount of the Liability and Equity (Details) - Convertible Senior Notes - USD ($) $ in Thousands	Apr. 30, 2020	Sep. 21, 2018
2023 Notes
Liability component:
Principal amount	$ 1,265,000	$ 1,270,000
Unamortized discount	(188,675)
Unamortized issuance costs	(7,363)
Net carrying amount	1,068,962
Equity component, net of purchase discounts and issuance costs	264,129
2025 Notes
Liability component:
Principal amount	862,500	$ 862,500
Unamortized discount	(191,156)
Unamortized issuance costs	(5,260)
Net carrying amount	666,084
Equity component, net of purchase discounts and issuance costs	$ 234,712