Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 171	$ 173	$ 102
Additions (Reductions) Charged to Cost and Expenses	200	108	184
Other	0	0	0
Deductions	(223)	(110)	(113)
Balance at End of Year	148	171	173
Reserve for Cash Discounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	827	746	727
Additions (Reductions) Charged to Cost and Expenses	10,027	9,570	8,859
Other	0	0	0
Deductions	(9,875)	(9,489)	(8,840)
Balance at End of Year	979	827	746
Reserve for Sales Returns and Allowances [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	1,782	1,594	1,639
Additions (Reductions) Charged to Cost and Expenses	7,962	7,833	7,326
Other	0	0	0
Deductions	(7,613)	(7,645)	(7,371)
Balance at End of Year	$ 2,131	$ 1,782	$ 1,594