Equity-Based Compensation - Stock Option Activity (Details) - Stock Options - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended		12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Apr. 30, 2017
Number of Options
Outstanding, beginning of the period (in shares)	2,088
Options granted (in shares)	63
Options exercised (in shares)	(171)	0
Outstanding, end of the period (in shares)	1,980		2,088
Exercisable at end of period (in shares)	1,559
Vested and expected to vest at end of period (in shares)	1,980
Weighted Average Exercise Price
Outstanding, beginning of period (in dollars per share)	$ 13.49
Options granted (in dollars per share)	37.49
Options exercised (in dollars per share)	12.56
Outstanding, end of the period (in dollars per share)	14.34		$ 13.49
Exercisable at end of period (in dollars per share)	12.89
Vested and expected to vest at end of period (in dollars per share)	$ 14.34
Other disclosures
Weighted Average Remaining Contractual Life, Outstanding (in years)	6 years 6 months 29 days		7 years 2 months 23 days
Weighted Average Remaining Contractual Life, Exercisable at end of period (in years)	6 years 3 months 29 days
Weighted Average Remaining Contractual Life, Vested and expected to vest at end of period (in years)	7 years 6 months 7 days
Aggregate Intrinsic Value, Outstanding	$ 39,493		$ 47,336
Aggregate Intrinsic Value, Exercisable at end of period	33,339
Aggregate Intrinsic Value, Vested and expected to vest at end of period	39,493
Intrinsic value of options exercised	3,700
Unrecognized compensation cost	$ 1,300
Weighted-average period for recognition of unrecognized compensation expense (in years)	2 years 2 months 12 days