Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended			6 Months Ended
		Oct. 31, 2016		Oct. 31, 2015	Oct. 31, 2016		Oct. 31, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total	[1]	$ 0.01		$ 0.08	$ 0.07		$ 0.16
Basic weighted average common shares outstanding		29,135		28,660	29,037		28,637
Class A Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings		$ 0.11		$ 0.10	$ 0.21		$ 0.20
Undistributed earnings		(0.10)		(0.02)	(0.14)		(0.04)
Total		$ 0.01	[2]	$ 0.08	$ 0.07	[2]	$ 0.16
Distributed earnings		$ 2,943		$ 2,610	$ 5,609		$ 5,215
Undistributed earnings		(2,565)		(651)	(3,680)		(916)
Total		$ 378		$ 1,959	$ 1,929		$ 4,299
Basic weighted average common shares outstanding		26,703		26,073	26,580		26,050
Class B Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings		$ 0.11		$ 0.10	$ 0.21		$ 0.20
Undistributed earnings		(0.10)		(0.02)	(0.14)		(0.04)
Total		$ 0.01	[2]	$ 0.08	$ 0.07	[2]	$ 0.16
Distributed earnings		$ 268		$ 259	$ 511		$ 517
Undistributed earnings		(234)		(65)	(340)		(91)
Total		$ 34		$ 194	$ 171		$ 426
Basic weighted average common shares outstanding		2,432		2,587	2,457		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 $0.01 and $0.08 for the three months ended October 31, 2016 and 2015, and $0.07 and $0.16 for the six months ended October 31, 2016 and 2015, respectively. See Note D to the Condensed Consolidated Financial Statements.

[2] Amounts adjusted for rounding