Convertible Senior Notes (Details)	1 Months Ended	6 Months Ended
	Apr. 30, 2018 USD ($) day shares $ / shares	Jul. 31, 2018 USD ($) $ / shares	Jul. 31, 2017 USD ($)	[1]	Apr. 04, 2018 $ / shares
Debt Instrument [Line Items]
Proceeds from issuance of convertible senior notes, net of issuance costs		$ 562,062,000	$ 0
Debt issuance costs, net of amortization	$ 12,900,000
Closing price of stock (in dollars per share) | $ / shares		$ 21.66
Payment to enter into agreement		$ 64,630,000	$ 0
Capped Call
Debt Instrument [Line Items]
Payment to enter into agreement	64,600,000
Convertible Senior Notes
Debt Instrument [Line Items]
Debt issuance costs, net of amortization	9,800,000	9,337,000
Additional Paid-in Capital
Debt Instrument [Line Items]
Debt issuance costs, net of amortization	$ 3,100,000	$ 3,068,000
Class A
Debt Instrument [Line Items]
Closing price of stock (in dollars per share) | $ / shares		$ 21.66			$ 19.83
Class A | Capped Call
Debt Instrument [Line Items]
Exercise price (in dollars per share) | $ / shares	$ 39.66
Exercise price premium percentage over last reported sales price					100.00%
Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount	$ 575,000,000.0
Interest rate	0.125%
Proceeds from issuance of convertible senior notes, net of issuance costs	$ 562,100,000
Conversion percentage of principal amount plus accrued and unpaid contingent interest	100.00%
Convertible debt, fair value based on the closing trading price per $100 of the Notes		$ 607,200,000
If-converted value		$ 474,000,000
Convertible Senior Notes | Class A
Debt Instrument [Line Items]
Number of convertible shares at initial conversion rate (in shares) | shares	21,884,155
Conversion ratio (in shares per $1,000 principal amount)	38.0594
Conversion price (in dollars per share) | $ / shares	$ 26.27
Redemption percentage of principal amount of Notes to be redeemed	100.00%
Convertible Senior Notes | Class A | Any Fiscal Quarter Commencing After The Fiscal Quarter Ending On July 31, 2018
Debt Instrument [Line Items]
Threshold trading days | day	20
Threshold consecutive trading days | day	30
Threshold percentage of stock price trigger	130.00%
Convertible Senior Notes | Class A | Five Business Day Period After Any Five Consecutive Trading Day Period
Debt Instrument [Line Items]
Threshold consecutive trading days | day	5
Threshold percentage of stock price trigger	98.00%
Threshold business days | day	5
Convertible Senior Notes | Class A | Immediately Preceding The Date On Which We Provide Notice Of Redemption
Debt Instrument [Line Items]
Threshold trading days | day	2

[1] * Prior period information has been adjusted to reflect the adoption impact of ASC 606 and ASU 2016-18, which we adopted on February 1, 2018