Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total per share	[1]	$ 0.50	$ 0.36	$ 0.29
Basic weighted average common shares		29,232	28,727	28,283
Class A Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings per share		$ 0.44	$ 0.40	$ 0.40
Undistributed earnings/(loss) per share		0.06	(0.04)	(0.11)
Total per share	[2]	$ 0.50	$ 0.36	$ 0.29
Distributed earnings		$ 11,845	$ 10,479	$ 10,301
Undistributed earnings/(loss)		1,568	(1,148)	(2,914)
Total		$ 13,413	$ 9,331	$ 7,387
Basic weighted average common shares		26,793	26,143	25,696
Class B Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings per share		$ 0.44	$ 0.40	$ 0.40
Undistributed earnings/(loss) per share		0.06	(0.04)	(0.11)
Total per share	[2]	$ 0.50	$ 0.35	$ 0.29
Distributed earnings		$ 1,066	$ 1,025	$ 1,035
Undistributed earnings/(loss)		142	(114)	(294)
Total		$ 1,208	$ 911	$ 741
Basic weighted average common shares		2,439	2,584	2,587

[1] Basic per share amounts are the same for Class A and Class B shares. Diluted per share amounts for Class A shares are shown above. Diluted per share for Class B shares under the two-class method are $0.49, $0.35 and $0.29 for the years ended April 30, 2017, 2016 and 2015, respectively. See Note 1 to the Consolidated Financial Statements.

[2] Amounts adjusted for rounding