Goodwill and Intangible Assets - Amortization (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Intangible assets
Amortization expense	$ 10,690	$ 10,820	$ 21,045	$ 20,233
Depreciation and amortization expense
Intangible assets
Amortization expense	$ 10,700	$ 10,800	$ 21,000	$ 20,200