Convertible Senior Notes - Allocation of Notes (Details) - USD ($) $ in Thousands	Apr. 30, 2018	Jul. 31, 2018
Liability:
Less: debt issuance costs, net of amortization	$ (12,900)
Stockholders' equity:
Less: debt issuance costs	(12,900)
Convertible Senior Notes
Liability:
Principal		$ 575,000
Less: debt discount, net of amortization		(128,976)
Less: debt issuance costs, net of amortization	(9,800)	(9,337)
Net carrying amount of the Notes		436,687
Stockholders' equity:
Less: debt issuance costs	(9,800)	(9,337)
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