Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 148	$ 171	$ 173
Additions (Reductions) Charged to Cost and Expenses	169	200	108
Other	78	0	0
Deductions	(136)	(223)	(110)
Balance at End of Year	259	148	171
Reserve for Cash Discounts [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	979	827	746
Additions (Reductions) Charged to Cost and Expenses	11,999	10,027	9,570
Other	584	0	0
Deductions	(11,935)	(9,875)	(9,489)
Balance at End of Year	1,627	979	827
Reserve for Sales Returns and Allowances [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	2,131	1,782	1,594
Additions (Reductions) Charged to Cost and Expenses	11,318	7,962	7,833
Other	1,829	0	0
Deductions	(10,897)	(7,613)	(7,645)
Balance at End of Year	$ 4,381	$ 2,131	$ 1,782