Equity Incentive Plans - Equity Incentive Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jul. 31, 2019	Jan. 31, 2019	Apr. 04, 2018
Options Outstanding, Number of Shares
Beginning balance (in shares)	35,465,543
Options exercised (in shares)	(3,862,965)
Options forfeited/cancelled (in shares)	(343,662)
Ending balance (in shares)	31,258,916	35,465,543
Vested and exercisable (in shares)	25,407,263
Options Outstanding, Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 8.34
Options exercised (in dollars per share)	4.99
Options forfeited/cancelled (in dollars per share)	15.49
Ending balance (in dollars per share)	8.67	$ 8.34
Weighted Average Exercise Price, Vested and exercisable (in dollars per share)	$ 7.54
Weighted- Average Remaining Contractual Life
Weighted Average Remaining Contractual Life (in years)	3 years 10 months 24 days	5 years 4 months 24 days
Weighted Average Remaining Contractual Life, Vested and exercisable (in years)	4 years 9 months 18 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 218,450	$ 339,591
Aggregate Intrinsic Value, Vested and exercisable	$ 203,215
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Closing price of stock (in dollars per share)	$ 15.14
Unrecognized compensation cost, stock options	$ 20,600
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost (in years)	1 year 7 months 6 days
Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Closing price of stock (in dollars per share)	$ 15.14		$ 19.83
2015 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost (in years)	1 year 6 months