Basic Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Oct. 31, 2014		Oct. 31, 2013		Oct. 31, 2014		Oct. 31, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total	$ 0.04	[1]	$ 0.13	[1]	$ 0.10	[1]	$ 0.19	[1]
Basic weighted average common shares outstanding	28,270		27,448		28,252		27,406
Class A Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings	$ 0.10		$ 0.10		$ 0.20		$ 0.10
Undistributed earnings	$ (0.06)		$ 0.03		$ (0.10)		$ 0.09
Total	$ 0.04		$ 0.13		$ 0.10		$ 0.19
Distributed earnings	$ 2,566		$ 2,492		$ 5,133		$ 2,492
Undistributed earnings	(1,499)		853		(2,672)		2,296
Total	1,067		3,345		2,461		4,788
Basic weighted average common shares outstanding	25,683		24,861		25,665		24,819
Class B Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings	$ 0.10		$ 0.10		$ 0.20		$ 0.10
Undistributed earnings	$ (0.06)		$ 0.03		$ (0.10)		$ 0.09
Total	$ 0.04		$ 0.13		$ 0.10		$ 0.19
Distributed earnings	259		259		517		259
Undistributed earnings	(151)		89		(269)		239
Total	$ 108		$ 348		$ 248		$ 498
Basic weighted average common shares outstanding	2,587		2,587		2,587		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 $0.04 and $0.13 for the three months ended October 31, 2014 and 2013 and $0.10 and $0.19 for the six months ended October 31, 2014 and 2013, respectively. See Note D to the Condensed Consolidated Financial Statements.