Convertible Senior Notes - Allocation of Notes (Details) $ in Thousands	Apr. 30, 2018 USD ($)
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	(134,976)
Less: debt issuance costs, net of amortization	(9,772)
Net carrying amount of the Notes	430,252
Stockholders' equity:
Less: debt issuance costs	(9,772)
Additional Paid-in Capital
Liability:
Less: debt issuance costs, net of amortization	(3,068)
Stockholders' equity:
Allocated value of the conversion feature	136,333
Less: debt issuance costs	(3,068)
Additional paid-in capital	$ 133,265