Income Taxes (Schedule of Valuation Allowance) (Details) - Valuation allowance - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of the year	$ 49,215	$ 22,844	$ 21,515
Charged to costs and expenses	2,302	26,371	3,281
Charged to other accounts	0	0	0
Deductions	(4,447)	0	(1,952)
Balance, end of the year	$ 47,070	$ 49,215	$ 22,844