Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Apr. 30, 2017	Apr. 30, 2016
Allowance for doubtful accounts receivable	$ 171	$ 178
Class A treasury stock, shares	4,588,632	4,588,632
Class A Common Shares
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	31,821,508	30,972,947
Common stock, shares outstanding	31,821,508	30,972,947
Class B Common Shares
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares issued	2,393,336	2,487,086
Common stock, shares outstanding	2,393,336	2,487,086