Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($)	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019
Number of shares
Options outstanding, Beginning Balance	12,961,397
Options granted	2,502,908
Options exercised	(1,665,778)
Options forfeited/cancelled	(350,501)
Options outstanding, Ending Balance	13,448,026	12,961,397
Options vested and exercisable	6,697,955
Options vested and exercisable and expected to vest thereafter	13,448,026
Weighted average exercise price
Options outstanding, Beginning Balance	$ 19.43
Options granted	129.79
Options exercised	6.54
Options forfeited/cancelled	55.16
Options outstanding, Ending Balance	40.64	$ 19.43
Options vested and exercisable	6.19
Options vested and exercisable and expected to vest thereafter	$ 40.64
Weighted average remaining contractual term (in years), options outstanding	5 years 4 months 24 days	5 years 4 months 24 days
Weighted average remaining contractual term (in years), options vested and exercisable	3 years 2 months 12 days
Weighted average remaining contractual term (in years), options vested and exercisable and expected to vest thereafter	5 years 4 months 24 days
Aggregate intrinsic value
Options outstanding	$ 1,426,502,005	$ 1,161,695,032
Options vested and exercisable	940,544,986
Options vested and exercisable and expected to vest thereafter	$ 1,426,502,005