Income Taxes (Schedule of Valuation Allowance) (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2018
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Charged to costs and expenses	$ 2,200
Deductions	(4,100)
Valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of the year	47,070	$ 49,215	$ 22,844
Charged to costs and expenses	2,151	2,302	26,371
Charged to other accounts	0	0	0
Deductions	(4,097)	(4,447)	0
Balance, end of the year	$ 45,124	$ 47,070	$ 49,215