Stockholders' Equity - Summary of Stock Option Activity (Detail)	12 Months Ended
	Jan. 31, 2018 USD ($) $ / shares shares	Jan. 31, 2017 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of shares, Options outstanding, Beginning Balance | shares	16,282,343
Number of shares, Options granted | shares	2,879,635
Number of shares, Options exercised | shares	(2,935,962)
Number of shares, Options forfeited/cancelled | shares	(201,870)
Number of shares, Options outstanding, Ending Balance | shares	16,024,146	16,282,343
Number of shares, Options vested and exercisable | shares	6,319,293
Number of shares, Options vested and exercisable and expected to vest thereafter | shares	16,024,146
Weighted average exercise price, Options outstanding, Beginning Balance | $ / shares	$ 7.48
Weighted average exercise price, Options granted | $ / shares	59.97
Weighted average exercise price, Options exercised | $ / shares	7.22
Weighted average exercise price, Options forfeited/cancelled | $ / shares	22.84
Weighted average exercise price, Options outstanding, Ending Balance | $ / shares	16.76	$ 7.48
Weighted average exercise price, Options vested and exercisable | $ / shares	5.47
Weighted average exercise price, Options vested and exercisable and expected to vest thereafter | $ / shares	$ 16.76
Weighted average remaining contractual term (in years), Options outstanding	6 years 1 month 6 days	6 years 3 months 18 days
Weighted average remaining contractual term (in years), Options vested and exercisable	4 years 10 months 24 days
Weighted average remaining contractual term (in years), Options vested and exercisable and expected to vest thereafter	6 years 1 month 6 days
Aggregate intrinsic value, Options outstanding | $	$ 738,648,507	$ 567,491,532
Aggregate intrinsic value, Options vested and exercisable | $	362,644,996
Aggregate intrinsic value, Options vested and exercisable and expected to vest thereafter | $	$ 738,648,507