Income Taxes - Net Operating Loss Carryforwards and Valuation Allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
Operating loss carryforwards
Net operating loss carry forwards		$ 700	$ 2,300
Valuation allowance
Valuation allowance	$ 10,183	1,112
Valuation allowance increase (decrease)	$ 7,600
State
Operating loss carryforwards
Net operating loss carry forwards		$ 27,400	$ 23,100