Overview and Basis of Presentation - Narrative (Details) - USD ($)				9 Months Ended
	Feb. 23, 2018	Apr. 07, 2017	Apr. 06, 2017	Oct. 31, 2018	Oct. 31, 2017	[1]
Class of Stock [Line Items]
Initial public offering costs				$ 0	$ 4,038,000
Class A Common Stock
Class of Stock [Line Items]
Price per share in initial public offering (in dollars per share)		$ 17.00
Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Redeemable convertible preferred stock converted to common class B stock (in shares)			59,491,640
Class B Common Stock
Class of Stock [Line Items]
Common class B stock after conversion of redeemable convertible stock (in shares)			59,491,640
Initial Public Offering
Class of Stock [Line Items]
Proceeds from initial public offering, net of underwriters' discounts and commissions		$ 200,000,000
Initial public offering costs		$ 5,600,000
Initial Public Offering | Class A Common Stock
Class of Stock [Line Items]
Shares issued in initial public offering (in shares)		12,650,000
Convertible Senior Notes Due 2023 | Senior Notes
Class of Stock [Line Items]
Aggregate principal amount	$ 345,000,000.0
Fixed interest rate	0.25%
Gross proceeds from issuance of debt	$ 345,000,000
Issuance costs	$ 10,000,000			$ 10,000,000

[1] See Note 2 for a summary of adjustments.