Stockholders' Equity - Summary of Stock Option Activity (Detail)	9 Months Ended	12 Months Ended
	Oct. 31, 2019 USD ($) $ / shares shares	Jan. 31, 2019 USD ($) $ / shares shares
Number of shares
Options outstanding, Beginning balance (in shares) | shares	12,961,397
Options granted (in shares) | shares	1,475,355
Options exercised (in shares) | shares	(1,225,746)
Options forfeited/cancelled (in shares) | shares	(318,028)
Options outstanding, Ending balance (in shares) | shares	12,892,978	12,961,397
Options vested and exercisable (in shares) | shares	6,704,980
Options vested and exercisable and expected to vest thereafter (in shares) | shares	12,892,978
Weighted average exercise price
Options outstanding, Beginning balance (in usd per share) | $ / shares	$ 19.43
Options granted (in usd per share) | $ / shares
Options exercised (in usd per share) | $ / shares
Options forfeited/cancelled (in usd per share) | $ / shares
Options outstanding, Ending balance (in usd per share) | $ / shares	33.25	$ 19.43
Options vested and exercisable (in usd per share) | $ / shares	5.96
Options vested and exercisable and expected to vest thereafter (in usd per share) | $ / shares	$ 33.25
Weighted average remaining contractual term (in years), Options outstanding	5 years 2 months 12 days	5 years 4 months 24 days
Weighted average remaining contractual term (in years), Options vested and exercisable	3 years 4 months 24 days
Weighted average remaining contractual term (in years), Options vested and exercisable and expected to vest thereafter	5 years 2 months 12 days
Aggregate intrinsic value
Options outstanding | $	$ 1,401,940,929	$ 1,161,695,032
Options vested and exercisable | $	911,013,694
Options vested and exercisable and expected to vest thereafter | $	$ 1,401,940,929