Condensed 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 deficit	Treasury stock
Beginning balance (in shares) at Apr. 30, 2019					33,979,739	1,821,587
Beginning 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)		650,943			650,943
Proceeds from stock options exercised		$ 6,358			$ 65		6,293
Stock-based compensation		946					946
Net earnings		2,911						2,911
Dividends declared*	[1]	(6,956)						(6,956)
Ending balance (in shares) at Oct. 31, 2019					34,630,682	1,821,587
Ending balance at Oct. 31, 2019		117,866			$ 3,463	$ 182	145,554	(5,774)	(25,559)
Beginning balance (in shares) at Jul. 31, 2019					34,131,239	1,821,587
Beginning balance at Jul. 31, 2019		114,203			$ 3,413	$ 182	140,195	(4,028)	(25,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)					499,443
Proceeds from stock options exercised		4,906			$ 50		4,856
Stock-based compensation		503					503
Net earnings		1,759						1,759
Dividends declared*	[1]	(3,505)						(3,505)
Ending balance (in shares) at Oct. 31, 2019					34,630,682	1,821,587
Ending balance at Oct. 31, 2019		117,866			$ 3,463	$ 182	145,554	(5,774)	(25,559)
Beginning balance (in shares) at Apr. 30, 2020			35,000,649	1,821,587	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	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	[1]	692						692
Dividends declared*	[1]	(3,575)						(3,575)
Ending balance (in shares) at Oct. 31, 2020			35,277,846	1,821,587	35,277,846	1,821,587
Ending balance at Oct. 31, 2020		$ 119,053			$ 3,528	$ 182	$ 154,335	$ (13,433)	$ (25,559)

[1] Amounts adjusted for rounding