Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended			9 Months Ended
		Jan. 31, 2017		Jan. 31, 2016	Jan. 31, 2017		Jan. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total	[1]	$ 0.08		$ 0.07	$ 0.15		$ 0.24
Basic weighted average common shares outstanding		29,333		28,778	29,136		28,684
Class A Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings		$ 0.11		$ 0.10	$ 0.32		$ 0.30
Undistributed earnings		(0.03)		(0.03)	(0.17)		(0.06)
Total		$ 0.08	[2]	$ 0.07	$ 0.15	[2]	$ 0.24
Distributed earnings		$ 2,943		$ 2,626	$ 8,583		$ 7,841
Undistributed earnings		(887)		(704)	(4,596)		(1,620)
Total		$ 2,056		$ 1,922	$ 3,987		$ 6,221
Basic weighted average common shares outstanding		26,901		26,191	26,687		26,097
Class B Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings		$ 0.11		$ 0.10	$ 0.32		$ 0.30
Undistributed earnings		(0.03)		(0.03)	(0.17)		(0.06)
Total		$ 0.08	[2]	$ 0.07	$ 0.15	[2]	$ 0.24
Distributed earnings		$ 267		$ 259	$ 778		$ 776
Undistributed earnings		(80)		(70)	(422)		(161)
Total		$ 187		$ 189	$ 356		$ 615
Basic weighted average common shares outstanding		2,432		2,587	2,448		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 earnings per share for Class B shares under the two-class method are $0.08 and $0.07 for the three months ended January 31, 2017 and 2016, and $0.15 and $0.24 for the nine months ended January 31, 2017 and 2016, respectively. See Note D to the Condensed Consolidated Financial Statements.

[2] Amounts adjusted for rounding