Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Apr. 30, 2020	Jan. 31, 2020
Number of shares
Options outstanding, Beginning balance (in shares)	13,448,026
Options granted (in shares)	1,264,192
Options exercised (in shares)	(645,515)
Options forfeited/cancelled (in shares)	(44,252)
Options outstanding, Ending balance (in shares)	14,022,451	13,448,026
Options vested and exercisable (in shares)	6,759,113
Options vested and exercisable and expected to vest thereafter (in shares)	14,022,451
Weighted average exercise price
Options outstanding, Beginning balance (in usd per share)	$ 40.64
Options granted (in usd per share)	172.55
Options exercised (in usd per share)	15.92
Options forfeited/cancelled (in usd per share)	84.44
Options outstanding, Ending balance (in usd per share)	53.40	$ 40.64
Options vested and exercisable (in usd per share)	11.99
Options vested and exercisable and expected to vest thereafter (in usd per share)	$ 53.40
Weighted average remaining contractual term (in years), Options outstanding	5 years 7 months 6 days	5 years 4 months 24 days
Weighted average remaining contractual term (in years), Options vested and exercisable	3 years 3 months 18 days
Weighted average remaining contractual term (in years), Options vested and exercisable and expected to vest thereafter	5 years 7 months 6 days
Aggregate intrinsic value
Options outstanding	$ 1,926,725,769	$ 1,426,502,005
Options vested and exercisable	1,208,620,921
Options vested and exercisable and expected to vest thereafter	$ 1,926,725,769