Diluted Earnings Per Share for Class B Common Shares Using Two-Class Method (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended								12 Months Ended
		Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2017		Apr. 30, 2016		Apr. 30, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings		$ 10,278	$ 2,243	$ 412	$ 1,688	$ 3,406	$ 2,111	$ 2,153	$ 2,572	$ 14,621		$ 10,242		$ 8,128
Basic weighted average common shares outstanding										29,232		28,727		28,283
Weighted Average Number of Shares Outstanding, Diluted										29,567		29,005		28,614
Basic, EPS	[1]									$ 0.50		$ 0.36		$ 0.29
Diluted, EPS		$ 0.34	$ 0.08	$ 0.01	$ 0.06	$ 0.12	$ 0.07	$ 0.07	$ 0.09	$ 0.49	[1]	$ 0.35	[1]	$ 0.28	[1]
Class B Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed and Distributed Earnings, Class B conversion										$ 1,208		$ 911		$ 741
Reallocation of Undistributed Earnings										(2)		2		4
Net earnings										$ 1,206		$ 913		$ 745
Basic weighted average common shares outstanding										2,439		2,584		2,587
Weighted Average Number of Shares Outstanding, Diluted										2,439		2,584		2,587
Basic, EPS	[2]									$ 0.50		$ 0.35		$ 0.29
Diluted, EPS	[2]									$ 0.49		$ 0.35		$ 0.29

[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