Equity Incentive Plans - Narrative (Details)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 28, 2019 USD ($)	Oct. 31, 2019 USD ($) period shares	Oct. 31, 2018 USD ($)	Oct. 31, 2019 USD ($) plan period shares	Oct. 31, 2018 USD ($)	Dec. 31, 2015 USD ($)
Share-based Payment Arrangement [Abstract]
Number of equity incentive plans | plan				2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense		$ 54,229,000	$ 58,329,000	$ 174,790,000	$ 155,938,000
2015 Equity Incentive Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price as percentage of fair market value of common stock				100.00%
2015 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase plan offering period				24 months
Number of purchase periods | period		4		4
Purchase period, term				6 months
Total stock-based compensation expense		$ 4,300,000	$ 11,600,000	$ 20,000,000.0	$ 26,200,000
Unrecognized stock-based compensation expense		$ 33,100,000		$ 33,100,000
Compensation cost (in years)				1 year 10 months 24 days
2015 Employee Stock Purchase Plan | Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price as percentage of fair market value of common stock				85.00%
Payroll deductions percentage		30.00%		30.00%
Share cap for ESPP at purchase date (in shares) | shares		3,000		3,000
Calendar year gap for ESPP contribution amount						$ 25,000
Dollar cap per purchase period	$ 7,500
Modification charges				$ 11,400,000