Stockholders' Equity - Summary of Stock Option Activity (Detail)	6 Months Ended	12 Months Ended
	Jul. 31, 2017 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	13,000
Number of shares, Options exercised | shares	(1,918,647)
Number of shares, Options forfeited/cancelled | shares	(108,201)
Number of shares, Options outstanding, Ending Balance | shares	14,268,495	16,282,343
Number of shares, Options vested and exercisable | shares	5,648,977
Number of shares, Options vested and exercisable and expected to vest thereafter | shares	14,268,495
Weighted average exercise price, Options outstanding, Beginning Balance | $ / shares	$ 7.48
Weighted average exercise price, Options granted | $ / shares	57.37
Weighted average exercise price, Options exercised | $ / shares	7.06
Weighted average exercise price, Options forfeited/cancelled | $ / shares	21.87
Weighted average exercise price, Options outstanding, Ending Balance | $ / shares	7.47	$ 7.48
Weighted average exercise price, Options vested and exercisable | $ / shares	5.19
Weighted average exercise price, Options vested and exercisable and expected to vest thereafter | $ / shares	$ 7.47
Weighted average remaining contractual term (in years), Options outstanding	5 years 9 months 18 days	6 years 3 months 19 days
Weighted average remaining contractual term (in years), Options vested and exercisable	5 years 3 months 19 days
Weighted average remaining contractual term (in years), Options vested and exercisable and expected to vest thereafter	5 years 9 months 18 days
Aggregate intrinsic value, Options outstanding | $	$ 803,181,095	$ 567,491,532
Aggregate intrinsic value, Options vested and exercisable | $	330,863,470
Aggregate intrinsic value, Options vested and exercisable and expected to vest thereafter | $	$ 803,181,095