Consolidated Statements 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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)		456,113			456,109	[1]
Proceeds from stock options exercised	[1]	$ 4,003			$ 46			3,957
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	[1]	1,307						1,307
Net earnings		4,929							4,929
Dividends declared	[1]	(10,220)							(10,220)
Ending balance (in shares) at Jan. 31, 2019					33,833,676		1,821,587
Ending balance at Jan. 31, 2019		114,356			$ 3,383		$ 182	136,522	(172)	(25,559)
Beginning balance (in shares) at Oct. 31, 2018					33,721,076		1,821,587
Beginning balance at Oct. 31, 2018		114,088			$ 3,372		$ 182	135,150	943	(25,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)					112,600
Proceeds from stock options exercised		917			$ 11			906
Stock-based compensation		466						466
Net earnings		2,301							2,301
Dividends declared	[1]	(3,416)							(3,416)
Ending balance (in shares) at Jan. 31, 2019					33,833,676		1,821,587
Ending balance at Jan. 31, 2019		114,356			$ 3,383		$ 182	136,522	(172)	(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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)		802,444			802,444
Proceeds from stock options exercised		$ 7,837			$ 80			7,757
Stock-based compensation		1,510						1,510
Net earnings		6,197							6,197
Dividends declared	[1]	(10,479)							(10,479)
Ending balance (in shares) at Jan. 31, 2020			34,782,183	1,821,587	34,782,183		1,821,587
Ending balance at Jan. 31, 2020		119,672			$ 3,478		$ 182	147,582	(6,011)	(25,559)
Beginning balance (in shares) at Oct. 31, 2019					34,630,682		1,821,587
Beginning balance at Oct. 31, 2019		117,866			$ 3,463		$ 182	145,554	(5,774)	(25,559)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised (in shares)					151,501
Proceeds from stock options exercised		1,480			$ 15			1,465
Stock-based compensation	[1]	563						563
Net earnings		3,286							3,286
Dividends declared	[1]	(3,523)							(3,523)
Ending balance (in shares) at Jan. 31, 2020			34,782,183	1,821,587	34,782,183		1,821,587
Ending balance at Jan. 31, 2020		$ 119,672			$ 3,478		$ 182	$ 147,582	$ (6,011)	$ (25,559)

[1] Amounts adjusted for rounding