SCHEDULE II-VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2015
Allowance for doubtful accounts
Movement in valuation and qualifying accounts and reserves
Balance at Beginning of Period	$ 104	$ 56
Charged to Cost and Expenses	976	56	$ 158
Deductions		(8)	(326)
Balance at End of Period	1,080	104	224
Warranty reserve
Movement in valuation and qualifying accounts and reserves
Balance at Beginning of Period	1,947	3,094
Charged to Cost and Expenses	1,884	1,838	3,589
Charged to Other Accounts			(424)
Deductions	(1,741)	(2,985)	(1,758)
Balance at End of Period	2,090	1,947	1,687
Reserve for inventory excess and obsolescence
Movement in valuation and qualifying accounts and reserves
Balance at Beginning of Period	2,756	2,542
Charged to Cost and Expenses	2,758	1,115	2,762
Deductions	(1,561)	(901)	(2,046)
Balance at End of Period	3,953	2,756	1,826
Reserve for self-insured medical claims
Movement in valuation and qualifying accounts and reserves
Balance at Beginning of Period	1,133	979
Charged to Cost and Expenses	9,100	7,037	7,668
Deductions	(9,230)	(6,883)	(7,742)
Balance at End of Period	$ 1,003	$ 1,133	$ 1,053