Consolidated Statements of Shareholders' Equity (USD $) In Thousands, except Share data	Total	Class A Common Shares	Class B Common Shares	Additional Paid-in Capital	Retained Earnings	Treasury Stock
Beginning Balance at Apr. 30, 2011	$ 74,056	$ 2,765	$ 275	$ 88,278	$ 6,257	$ (23,519)
Beginning Balance (in shares) at Apr. 30, 2011		27,651,615	2,747,086
Proceeds from stock options exercised (in shares)	986,875	986,875
Proceeds from stock options exercised	5,039	99		4,940
Stock-based compensation	1,287			1,287
Conversion of Class B shares into Class A shares (in shares)		160,000	(160,000)
Conversion of Class B shares into Class A shares		16	(16)
Net earnings	11,343				11,343
Dividends declared	(9,576)				(9,576)
Tax benefit of stock option exercises	881			881
Ending Balance at Apr. 30, 2012	83,030	2,880	259	95,386	8,024	(23,519)
Ending Balance (in shares) at Apr. 30, 2012		28,798,490	2,587,086
Proceeds from stock options exercised (in shares)	386,356	386,356
Proceeds from stock options exercised	1,990	38		1,952
Stock-based compensation	1,476			1,476
Net earnings	10,411				10,411
Dividends declared	(13,037)				(13,037)
Repurchase of common shares	(759)					(759)
Tax benefit of stock option exercises	133			133
Ending Balance at Apr. 30, 2013	83,244	2,918	259	98,947	5,398	(24,278)
Ending Balance (in shares) at Apr. 30, 2013		29,184,846	2,587,086
Proceeds from stock options exercised (in shares)	890,341	890,341
Proceeds from stock options exercised	5,476	90		5,386
Stock-based compensation	1,509			1,509
Net earnings	10,331				10,331
Dividends declared	(8,361)				(8,361)
Tax benefit of stock option exercises	361			361
Ending Balance at Apr. 30, 2014	$ 92,560	$ 3,008	$ 259	$ 106,203	$ 7,368	$ (24,278)
Ending Balance (in shares) at Apr. 30, 2014		30,075,187	2,587,086
Ending Balance (in shares) at Apr. 30, 2014		30,075,187	2,587,086