Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Apr. 30, 2018	Jan. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of shares, Options outstanding, Beginning Balance	16,024,146
Number of shares, Options granted	175,000
Number of shares, Options exercised	(788,378)
Number of shares, Options forfeited/cancelled	(153,551)
Number of shares, Options outstanding, Ending Balance	15,257,217	16,024,146
Number of shares, Options vested and exercisable	6,342,353
Number of shares, Options vested and exercisable and expected to vest thereafter	15,257,217
Weighted average exercise price, Options outstanding, Beginning Balance	$ 16.76
Weighted average exercise price, Options granted	77.88
Weighted average exercise price, Options exercised	9.30
Weighted average exercise price, Options forfeited/cancelled	4.00
Weighted average exercise price, Options outstanding, Ending Balance	17.98	$ 16.76
Weighted average exercise price, Options vested and exercisable	5.47
Weighted average exercise price, Options vested and exercisable and expected to vest thereafter	$ 17.98
Weighted average remaining contractual term (in years), Options outstanding	6 years	6 years 1 month 6 days
Weighted average remaining contractual term (in years), Options vested and exercisable	4 years 8 months 12 days
Weighted average remaining contractual term (in years), Options vested and exercisable and expected to vest thereafter	6 years
Aggregate intrinsic value, Options outstanding	$ 797,016,507	$ 738,648,507
Aggregate intrinsic value, Options vested and exercisable	410,121,313
Aggregate intrinsic value, Options vested and exercisable and expected to vest thereafter	$ 797,016,507