Basic Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Oct. 31, 2013		Oct. 31, 2012		Oct. 31, 2013		Oct. 31, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total	$ 0.13	[1]	$ 0.10	[1]	$ 0.19	[1]	$ 0.19	[1]
Basic weighted average common shares outstanding	27,448		27,151		27,406		27,112
Class A Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings	$ 0.10		$ 0.09		$ 0.10		$ 0.18
Undistributed earnings	$ 0.03		$ 0.01		$ 0.09		$ 0.01
Total	$ 0.13		$ 0.10		$ 0.19		$ 0.19
Distributed earnings	$ 2,492		$ 2,211		$ 2,492		$ 4,420
Undistributed earnings	853		296		2,296		278
Total	3,345		2,507		4,788		4,698
Basic weighted average common shares outstanding	24,861		24,564		24,818		24,525
Class B Common Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributed earnings	$ 0.10		$ 0.09		$ 0.10		$ 0.18
Undistributed earnings	$ 0.03		$ 0.01		$ 0.09		$ 0.01
Total	$ 0.13		$ 0.10		$ 0.19		$ 0.19
Distributed earnings	259		233		259		466
Undistributed earnings	89		31		239		29
Total	$ 348		$ 264		$ 498		$ 495
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 $0.13 and $0.10 for the three months ended October 31, 2013 and 2012 and $0.19 for the six months ended October 31, 2013 and 2012, respectively. See Note D to the Condensed Consolidated Financial Statements.