Equity-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018	Apr. 30, 2018
Other disclosures
Equity-based compensation	$ 1,140	$ 430	$ 2,638	$ 1,277
Selling, general and administrative expenses
Other disclosures
Equity-based compensation			$ 2,600	$ 1,300
Stock Options
Number of Options
Outstanding, beginning of the period (in shares)			1,952
Options granted (in shares)			374	0
Options exercised (in shares)			(103)
Options forfeited (in shares)			(41)
Outstanding, end of the period (in shares)	2,182		2,182		1,952
Exercisable at end of period (in shares)	1,724		1,724
Vested and expected to vest at end of period (in shares)	2,173		2,173
Weighted Average Exercise Price
Outstanding, beginning of period (in dollars per share)			$ 14.37
Options granted (in dollars per share)			25.58
Options exercised (in dollars per share)			12.41
Options forfeited (in dollars per share)			27.00
Outstanding, end of the period (in dollars per share)	$ 16.15		16.15		$ 14.37
Exercisable at end of period (in dollars per share)	13.51		13.51
Vested and expected to vest at end of period (in dollars per share)	$ 16.10		$ 16.10
Other disclosures
Weighted Average Remaining Contractual Life, Outstanding (in years)			6 years 4 months 6 days		6 years 6 months 7 days
Weighted Average Remaining Contractual Life, Exercisable at end of period (in years)			5 years 7 months 17 days
Weighted Average Remaining Contractual Life, Vested and expected to vest at end of period (in years)			6 years 4 months 2 days
Aggregate Intrinsic Value, Outstanding	$ 10,261		$ 10,261		$ 33,209
Aggregate Intrinsic Value, Exercisable at end of period	10,217		10,217
Aggregate Intrinsic Value, Vested and expected to vest at end of period	10,260		10,260
Intrinsic value of options exercised			800	$ 3,700
Unrecognized compensation cost	$ 3,200		$ 3,200
Weighted-average period for recognition of unrecognized compensation expense (in years)			2 years 3 months 18 days