Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Total	Class A Common Shares	Class B Common Shares	Common Stock Class A Common Shares	Common Stock Class B Common Shares	Additional Paid-in Capital	Retained Earnings	Treasury Stock
Beginning balance (in shares) at Apr. 30, 2018				33,141,764	2,057,390
Beginning balance at Apr. 30, 2018	$ 112,584			$ 3,314	$ 205	$ 131,258	$ 3,366	$ (25,559)
Proceeds from stock options exercised (in shares)	295,813			295,809
Proceeds from stock options exercised	$ 2,666			$ 30		2,636
Conversion of Class B shares into Class A shares (in shares)				235,803	(235,803)
Conversion of Class B shares into Class A shares				$ 23	$ (23)
Stock-based compensation	398					398
Net earnings	1,385						1,385
Dividends declared	(3,399)						(3,399)
Ending balance (in shares) at Jul. 31, 2018				33,673,376	1,821,587
Ending balance at Jul. 31, 2018	115,387			$ 3,367	$ 182	134,292	3,105	(25,559)
Beginning balance (in shares) at Apr. 30, 2019		33,979,739	1,821,587	33,979,739	1,821,587
Beginning balance at Apr. 30, 2019	$ 114,607			$ 3,398	$ 182	138,315	(1,729)	(25,559)
Proceeds from stock options exercised (in shares)	151,500			151,500
Proceeds from stock options exercised	$ 1,452			$ 15		1,437
Stock-based compensation	443					443
Net earnings	1,152						1,152
Dividends declared	(3,451)						(3,451)
Ending balance (in shares) at Jul. 31, 2019		34,131,239	1,821,587	34,131,239	1,821,587
Ending balance at Jul. 31, 2019	$ 114,203			$ 3,413	$ 182	$ 140,195	$ (4,028)	$ (25,559)