Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Allowance for Doubtful Accounts
Allowance Rollforward
Balance at beginning of period	$ (8,607)	$ (8,633)	$ (2,752)
Provision / Additions charged to costs and expenses	(1,792)	(908)	(5,828)
Charged to other accounts	(819)	77	(1,158)
Deductions	1,367	857	1,105
Balance at end of period	(9,851)	(8,607)	(8,633)
Valuation Allowance on Deferred Tax Assets
Allowance Rollforward
Balance at beginning of period	(83)	(143)	(1,276)
Provision / Additions charged to costs and expenses	(255)	(38)	(67)
Deductions	41	98	1,200
Balance at end of period	$ (297)	$ (83)	$ (143)