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Consolidated Statements of Shareholders' 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/deficit	Treasury stock
Beginning Balance (in shares) at Apr. 30, 2017				31,821,508	2,393,336
Beginning Balance at Apr. 30, 2017	$ 103,750			$ 3,182	$ 239	$ 121,280	$ 4,608	$ (25,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)	984,310			984,310
Proceeds from stock options exercised	$ 8,609			$ 98		8,511
Conversion of Class B shares into Class A shares (in shares)				335,946	(335,946)
Conversion of Class B shares into Class A shares				$ 34	$ (34)
Stock-based compensation	1,467					1,467
Net earnings	12,053						12,053
Dividends declared	(13,295)						(13,295)
Ending Balance (in shares) at Apr. 30, 2018				33,141,764	2,057,390
Ending Balance at Apr. 30, 2018	$ 112,584			$ 3,314	$ 205	131,258	3,366	(25,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)	602,176			602,176
Proceeds from stock options exercised	$ 5,367			$ 61		5,306
Conversion of Class B shares into Class A shares (in shares)				235,799	(235,803)
Conversion of Class B shares into Class A shares				$ 23	$ (23)
Stock-based compensation	1,751					1,751
Net earnings	6,803						6,803
Dividends declared	(13,651)						(13,651)
Ending Balance (in shares) at Apr. 30, 2019		33,979,739	1,821,587	33,979,739	1,821,587
Ending Balance at Apr. 30, 2019	$ 114,607			$ 3,398	$ 182	138,315	(1,729)	(25,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)	1,020,910			1,020,910
Proceeds from stock options exercised	$ 10,072			$ 102		9,970
Stock-based compensation	2,027					2,027
Net earnings	6,742						6,742
Dividends declared	(14,026)						(14,026)
Ending Balance (in shares) at Apr. 30, 2020		35,000,649	1,821,587	35,000,649	1,821,587
Ending Balance at Apr. 30, 2020	$ 119,422			$ 3,500	$ 182	$ 150,312	$ (9,013)	$ (25,559)