Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - 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 deficit	Treasury stock
Beginning balance (in shares) at Apr. 30, 2020					35,000,649		1,821,587
Beginning balance at Apr. 30, 2020		$ 119,422			$ 3,500		$ 182	$ 150,312	$ (9,013)	$ (25,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)		277,197			277,197
Proceeds from stock options exercised		$ 2,853			$ 28			2,825
Stock-based compensation		1,198						1,198
Net earnings		2,726							2,726
Dividends declared*	[1]	(7,146)							(7,146)
Ending balance (in shares) at Oct. 31, 2020					35,277,846		1,821,587
Ending balance at Oct. 31, 2020		119,053			$ 3,528		$ 182	154,335	(13,433)	(25,559)
Beginning balance (in shares) at Jul. 31, 2020					35,231,396		1,821,587
Beginning balance at Jul. 31, 2020		120,814			$ 3,523		$ 182	153,218	(10,550)	(25,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)					46,450
Proceeds from stock options exercised		471			$ 5			466
Stock-based compensation		651						651
Net earnings		692							692
Dividends declared*	[1]	(3,575)							(3,575)
Ending balance (in shares) at Oct. 31, 2020					35,277,846		1,821,587
Ending balance at Oct. 31, 2020		119,053			$ 3,528		$ 182	154,335	(13,433)	(25,559)
Beginning balance (in shares) at Apr. 30, 2021			35,629,566	1,821,587	35,629,566		1,821,587
Beginning balance at Apr. 30, 2021		$ 122,391			$ 3,563		$ 182	159,492	(15,287)	(25,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)		545,242			545,242	[1]
Proceeds from stock options exercised	[1]	$ 5,714			$ 54			5,660
Stock-based compensation		1,817						1,817
Net earnings		6,261							6,261
Dividends declared*	[1]	(7,336)							(7,336)
Ending balance (in shares) at Oct. 31, 2021			36,174,808	1,821,587	36,174,808		1,821,587
Ending balance at Oct. 31, 2021		128,847			$ 3,617		$ 182	166,969	(16,362)	(25,559)
Beginning balance (in shares) at Jul. 31, 2021					36,028,566		1,821,587
Beginning balance at Jul. 31, 2021		126,534			$ 3,603		$ 182	164,299	(15,991)	(25,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)	[1]				146,242
Proceeds from stock options exercised	[1]	1,642			$ 14			1,628
Stock-based compensation		1,042						1,042
Net earnings		3,314							3,314
Dividends declared*	[1]	(3,685)							(3,685)
Ending balance (in shares) at Oct. 31, 2021			36,174,808	1,821,587	36,174,808		1,821,587
Ending balance at Oct. 31, 2021		$ 128,847			$ 3,617		$ 182	$ 166,969	$ (16,362)	$ (25,559)

[1] Amounts adjusted for rounding