Fair Value Measurements - Schedule of Carrying Amounts and Estimated Fair Values of Convertible Note (Details) - Senior Notes - Convertible Senior Notes Due 2023 $ in Thousands	Apr. 30, 2018 USD ($)
Reported Value Measurement
Debt Instrument [Line Items]
Estimated Fair Value	$ 267,418
Estimate of Fair Value Measurement
Debt Instrument [Line Items]
Estimated Fair Value	$ 394,680

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant