Goodwill and Intangible Assets (Schedule of Goodwill) (Details) - USD ($) $ in Thousands	6 Months Ended
	Oct. 31, 2019	Oct. 31, 2018
Goodwill [Roll Forward]
Goodwill before impairment losses, beginning balance	$ 552,234	$ 540,168
Accumulated impairment losses, beginning balance	(32,297)	(32,297)
Goodwill, beginning balance	519,937	507,871
Acquisitions	8,491	624
Disposals and foreign currency changes, net	(2,589)	(1,304)
Impairments	0	0
Goodwill before impairment losses, ending balance	847,628	539,488
Accumulated impairment losses, ending balance	(32,297)	(32,297)
Goodwill, ending balance	815,331	$ 507,191
Wave
Goodwill [Roll Forward]
Acquisitions	$ 289,492