Equity Incentive Plans - Summary of Activity Under the Equity Incentive Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Options Outstanding, Number of Shares
Balance as of January 31, 2017 (in shares)	56,840,189
Options granted (in shares)	1,000,000
Options exercised (in shares)	(8,814,019)
Options cancelled/forfeited (in shares)	(2,666,221)
Balance as of January 31, 2018 (in shares)	46,359,949	56,840,189
Vested and exercisable as of January 31, 2018 (in shares)	28,990,955
Options Outstanding, Weighted- Average Exercise Price
Balance as of January 31, 2017 (in dollars per share)	$ 7.15
Options granted (in dollars per share)	14.92
Options exercised (in dollars per share)	2.79
Options cancelled/forfeited (in dollars per share)	13.91
Balance as of January 31, 2018 (in dollars per share)	7.75	$ 7.15
Vested and exercisable as of January 31, 2018 (in dollars per share)	$ 5.30
Weighted- Average Remaining Contractual Life (Years)
Weighted Average Remaining Contractual Life (Years)	6 years 3 months 18 days	7 years
Weighted Average Remaining Contractual Life (Years), Vested and exercisable	5 years 8 months 12 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 574,224	$ 315,502
Aggregate Intrinsic Value, Vested and exercisable	$ 430,325