Shareholders' Equity - Summary of Changes in Outstanding Options (Details) - USD ($)	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Number of Shares
Outstanding at May 1, 2017 (in shares)	3,275,836
Granted (in shares)	1,313,000
Exercised (in shares)	(602,176)	(984,310)	(754,811)
Forfeited (in shares)	(1,600)
Expired (in shares)	(2,000)
Outstanding at April 30, 2019 (in shares)	3,983,060	3,275,836
Exercisable at April 30, 2019	1,086,180
Weighted Average Exercise Price
Outstanding at May 1, 2017 (in shares)	$ 9.90
Granted (in usd per share)	12.41
Exercised (in usd per share)	8.89
Forfeited (in usd per share)	9.55
Expired (in usd per share)	8.11
Outstanding at April 30, 2019 (in shares)	10.88	$ 9.90
Exercisable at April 30, 2019 (in shares)	$ 9.80
Weighted Average Remaining Contractual Term
Outstanding at April 30, 2019 (in shares)	3 years 9 months 29 days
Exercisable at April 30, 2019 (in shares)	2 years 6 months 21 days
Aggregate Intrinsic Value
Outstanding at April 30, 2019 (in shares)	$ 8,662,677
Exercisable at April 30, 2019 (in shares)	$ 3,418,476