Income Taxes (Schedule of Valuation Allowance) (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Additions charged to costs and expenses	$ 3,200
Deductions	(13,500)
Valuation allowance, decrease in deferred tax asset	10,300
Valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of the year	45,124	$ 47,070	$ 49,215
Additions charged to costs and expenses	13,492	2,151	2,302
Deductions	(3,215)	(4,097)	(4,447)
Balance, end of the year	$ 55,401	$ 45,124	$ 47,070