Debt and Financing Arrangements - Schedule of Liability and Equity Component of 2023 Notes (Details) - Senior Notes - Convertible Senior Notes Due 2023 $ in Thousands	Apr. 30, 2018 USD ($)
Liability component:
Principal	$ 345,000
Less: unamortized debt issuance costs and debt discount	(85,080)
Net carrying amount	259,920
Additional Paid-in Capital
Equity component:
2023 Notes	79,962
Less: issuance costs	(2,320)
Carrying amount of the equity component	$ 77,642