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Convertible Senior Notes - Additional Information (Details)	2 Months Ended	9 Months Ended
	Jul. 31, 2018 USD ($) day $ / shares	Oct. 31, 2018 USD ($) $ / shares	Oct. 31, 2017 USD ($)	Jun. 30, 2018 USD ($)
Debt Instrument [Line Items]
Proceeds from borrowings on convertible senior notes, net of issuance costs	$ 291,100,000	$ 291,145,000	$ 0
Convertible debt, conversion ratio	14.6738
Convertible debt, conversion ratio denominator	$ 1,000
Initial conversion price (in dollars per share) | $ / shares	$ 68.15	$ 68.15
Consecutive threshold trading days | day	30
Threshold percentage of stock price trigger	130.00%
Carrying amount of convertible debt equity component	$ 84,200,000
Fair value of convertible debt		$ 403,200,000
Minimum
Debt Instrument [Line Items]
Threshold trading days | day	20
Redemption Period 1
Debt Instrument [Line Items]
Consecutive threshold trading days | day	30
Threshold percentage of stock price trigger	130.00%
Redemption Period 1 | Minimum
Debt Instrument [Line Items]
Threshold trading days | day	20
Redemption Period 2
Debt Instrument [Line Items]
Convertible debt, conversion ratio denominator	$ 1,000
Threshold trading days | day	5
Consecutive threshold trading days | day	5
Redemption Period 2 | Maximum
Debt Instrument [Line Items]
Trading price as a percentage of stock price and debt conversion rate	98.00%
Convertible Debt
Debt Instrument [Line Items]
Face amount of debt	$ 50,000,000			$ 250,000,000
Interest rate	0.75%			0.75%
Convertible debt, conversion ratio denominator		100
Percentage of principal amount redeemed	100.00%
Debt issuance costs	$ 8,800,000
Effective interest rate	7.03%
Convertible Debt | Convertible Senior Notes, Liability Component
Debt Instrument [Line Items]
Debt issuance costs	$ 6,300,000	6,111,000
Convertible Debt | Convertible Senior Notes, Equity Component
Debt Instrument [Line Items]
Carrying amount of convertible debt equity component		84,168,000
Debt issuance costs	$ 2,500,000	$ 2,485,000

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