Equity Incentive Plans - Summary of Activity Under the Equity Incentive Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018
Options Outstanding, Number of Shares
Balance at start of year (in shares)	46,359,949
Options exercised (in shares)	(9,397,220)
Options cancelled/forfeited (in shares)	(1,497,186)
Balance at end of year (in shares)	35,465,543	46,359,949
Vested and exercisable (in shares)	26,592,658
Options Outstanding, Weighted- Average Exercise Price
Balance at start of year (in dollars per share)	$ 7.75
Options exercised (in dollars per share)	5.08
Options cancelled/forfeited (in dollars per share)	10.55
Balance at end of year (in dollars per share)	8.34	$ 7.75
Vested and exercisable (in dollars per share)	$ 6.76
Weighted- Average Remaining Contractual Life (Years)
Weighted Average Remaining Contractual Life (Years)	5 years 4 months 24 days	6 years 3 months 18 days
Weighted Average Remaining Contractual Life (Years), Vested and exercisable	5 years 1 month 6 days
Aggregate Intrinsic Value (in thousands)
Aggregate Intrinsic Value	$ 339,591	$ 574,224
Aggregate Intrinsic Value, Vested and exercisable	$ 296,710