Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Class A Common Shares	Class B Common Shares	Additional Paid-in Capital	Retained Earnings	Treasury Stock
Beginning Balance at Apr. 30, 2014	$ 92,560	$ 3,008	$ 259	$ 106,203	$ 7,368	$ (24,278)
Beginning Balance (in shares) at Apr. 30, 2014		30,075,187	2,587,086
Proceeds from stock options exercised, shares	490,912	490,912
Proceeds from stock options exercised	$ 2,725	$ 49		2,676
Stock-based compensation	1,530			1,530
Net earnings	8,128				8,128
Dividends declared	(11,337)				(11,337)
Repurchase of common shares	(1,100)					(1,100)
Tax benefit of stock option exercises	420			420
Ending Balance at Apr. 30, 2015	$ 92,926	$ 3,057	$ 259	110,829	4,159	(25,378)
Ending Balance (in shares) at Apr. 30, 2015		30,566,099	2,587,086
Proceeds from stock options exercised, shares	306,848	306,848
Proceeds from stock options exercised	$ 1,818	$ 30		1,788
Conversion of Class B shares into Class A shares (in shares)		100,000	(100,000)
Conversion of Class B shares into Class A shares		$ 10	$ (10)
Stock-based compensation	1,593			1,593
Net earnings	10,242				10,242
Dividends declared	(11,504)				(11,504)
Repurchase of common shares	(181)					(181)
Ending Balance at Apr. 30, 2016	$ 94,894	$ 3,097	$ 249	114,210	2,897	(25,559)
Ending Balance (in shares) at Apr. 30, 2016		30,972,947	2,487,086
Proceeds from stock options exercised, shares	754,811	754,811
Proceeds from stock options exercised	$ 5,717	$ 75		5,642
Conversion of Class B shares into Class A shares (in shares)		93,750	(93,750)
Conversion of Class B shares into Class A shares		$ 10	$ (10)
Stock-based compensation	1,428			1,428
Net earnings	14,621				14,621
Dividends declared	(12,910)				(12,910)
Ending Balance at Apr. 30, 2017	$ 103,750	$ 3,182	$ 239	$ 121,280	$ 4,608	$ (25,559)
Ending Balance (in shares) at Apr. 30, 2017		31,821,508	2,393,336