Retirement Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Retirement Plan
Employee contributions matched by employer (as a percent)	50.00%
Employee compensation eligible for employer match of employee contributions (as a percent)	4.00%
Employer contributions to defined contribution retirement plan	$ 3,665	$ 1,743	$ 1,120