Convertible Debt (Details) - USD ($) $ in Thousands		3 Months Ended
	Oct. 31, 2018	Apr. 30, 2018	Apr. 30, 2019
Liability:
Less: debt issuance costs, net of amortization		$ (12,900)
Stockholders' equity:
Allocated value of the conversion feature		133,265
Less: debt issuance costs		(12,900)
Convertible Senior Notes
Liability:
Principal			$ 575,000
Less: debt discount, net of amortization			(110,670)
Less: debt issuance costs, net of amortization		(9,800)	(8,012)
Net carrying amount of the Notes			456,318
Stockholders' equity:
Less: debt issuance costs		(9,800)	(8,012)
Additional Paid-In Capital
Liability:
Less: debt issuance costs, net of amortization		(3,100)	(3,068)
Stockholders' equity:
Allocated value of the conversion feature	$ 136,333
Less: debt issuance costs		$ (3,100)	$ (3,068)
Additional paid-in capital	$ 133,265