Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Apr. 30, 2017	Jan. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of shares, Options outstanding, Beginning Balance	16,282,343
Number of shares, Options granted	6,500
Number of shares, Options exercised	(1,159,780)
Number of shares, Options forfeited/cancelled	(29,685)
Number of shares, Options outstanding, Ending Balance	15,099,378	16,282,343
Number of shares, Options vested and exercisable	5,533,574
Number of shares, Options vested and exercisable and expected to vest thereafter	15,099,378
Weighted average exercise price, Options outstanding, Beginning Balance	$ 7.48
Weighted average exercise price, Options granted	49.88
Weighted average exercise price, Options exercised	6.46
Weighted average exercise price, Options forfeited/cancelled	4.25
Weighted average exercise price, Options outstanding, Ending Balance	7.58	$ 7.48
Weighted average exercise price, Options vested and exercisable	5.29
Weighted average exercise price, Options vested and exercisable and expected to vest thereafter	$ 7.58
Weighted average remaining contractual term (in years), Options outstanding	6 years 1 month 6 days	6 years 3 months 19 days
Weighted average remaining contractual term (in years), Options vested and exercisable	5 years 6 months
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	$ 695,167,853	$ 567,491,532
Aggregate intrinsic value, Options vested and exercisable	267,439,117
Aggregate intrinsic value, Options vested and exercisable and expected to vest thereafter	$ 695,167,853