Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Jan. 31, 2017
Outstanding Stock Options
Balance, January 31, 2017 (in shares)	27,420,108
Options granted (in shares)	799,250
Options exercised (in shares)	(2,727,513)
Options forfeited (in shares)	(161,909)
Balance, April 30, 2017 (in shares)	25,329,936		27,420,108
Vested and expected to vest at April 30, 2017 (in shares)	24,276,268
Exercisable at April 30, 2017 (in shares)	13,624,390
Weighted-Average Exercise Price (in dollars per share):
Balance, January 31, 2017 (in dollars per share)	$ 4.24
Options granted (in dollars per share)	8.64
Options exercised (in dollars per share)	0.78
Options forfeited (in dollars per share)	6.36
Balance, April 30, 2017 (in dollars per share)	4.74		$ 4.24
Vested and expected to vest at April 30, 2017 (in dollars per share)	4.66
Exercisable at April 30, 2017 (in dollars per share)	$ 3.43
Balance, Weighted-Average Remaining Contractual Life (in years)	7 years 2 months 1 day		6 years 10 months 13 days
Vested and expected to vest at April 30, 2017, Weighted-Average Contractual Life (in years)	7 years 1 month 2 days
Exercisable at April 30, 2017, Weighted-Average Contractual Life (in years)	5 years 6 months 18 days
Balance, Aggregate Intrinsic Value	$ 256,380		$ 122,803
Vested and expected to vest at April 30, 2017, Aggregate Intrinsic Value	247,712
Exercisable at April 30, 2017, Aggregate Intrinsic Value	156,003
Options exercised, intrinsic value	$ 22,500	$ 800
Options granted, weighted-average grant date fair value (in dollars per share)	$ 5.01	$ 3.24