Equity-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Other disclosures
Share-based compensation expense	$ 1,695	$ 2,534	$ 2,699
Selling, general and administrative expenses
Other disclosures
Share-based compensation expense	$ 1,700	$ 2,400	$ 2,700
Stock Options
Number of Options
Outstanding, beginning of the period (in shares)	2,088,000
Options granted (in shares)	63,000		0
Options exercised (in shares)	(199,000)
Outstanding, end of the period (in shares)	1,952,000	2,088,000
Exercisable at end of period (in shares)	1,682,000
Vested and expected to vest at end of period (in shares)	1,946,000
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)	12.53
Outstanding, end of the period (in dollars per share)	14.37	$ 13.49
Exercisable at end of period (in dollars per share)	12.97
Vested and expected to vest at end of period (in dollars per share)	$ 14.33
Other disclosures
Weighted Average Remaining Contractual Life, Outstanding (in years)	6 years 6 months 7 days	7 years 2 months 23 days
Weighted Average Remaining Contractual Life, Exercisable at end of period (in years)	6 years 3 months 22 days
Weighted Average Remaining Contractual Life, Vested and expected to vest at end of period (in years)	6 years 6 months 7 days
Aggregate Intrinsic Value, Outstanding	$ 33,209	$ 47,336
Aggregate Intrinsic Value, Exercisable at end of period	30,599
Aggregate Intrinsic Value, Vested and expected to vest at end of period	33,173
Intrinsic value of options exercised	4,300	$ 600	$ 8,900
Unrecognized compensation cost	$ 1,100
Weighted-average period for recognition of unrecognized compensation expense (in years)	2 years 1 month 6 days
Stock Options | Selling, general and administrative expenses
Other disclosures
Share-based compensation expense	$ 1,700