Diluted Earnings Per Share for Class A Common Shares Using If-Converted Method (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Apr. 30, 2014		Jan. 31, 2014		Oct. 31, 2013		Jul. 31, 2013		Apr. 30, 2013		Jan. 31, 2013		Oct. 31, 2012		Jul. 31, 2012		Apr. 30, 2014		Apr. 30, 2013		Apr. 30, 2012
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings, Per Basic	$ 2,568		$ 2,477		$ 3,693		$ 1,593		$ 3,078		$ 2,140		$ 2,771		$ 2,422		$ 10,331		$ 10,411		$ 11,343
Basic weighted average common shares outstanding																	27,636		27,173		26,455
Diluted, Class A Common Shares																	28,111		27,629		27,098
Basic, EPS																	$ 0.37	[1]	$ 0.38	[1]	$ 0.43	[1]
Diluted, EPS	$ 0.09	[2]	$ 0.09	[2]	$ 0.13	[2]	$ 0.06	[2]	$ 0.11	[2]	$ 0.08	[2]	$ 0.10	[2]	$ 0.09	[2]	$ 0.37	[1],[2]	$ 0.38	[1],[2]	$ 0.42	[1]
Class A Common Shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Undistributed & distributed earnings, Per Basic																	9,370		9,419		10,237
Undistributed & distributed earnings, Class B Conversion																	961		992		1,106
Net Income (Loss) Available to Common Stockholders, Diluted, Total																	$ 10,331		$ 10,411		$ 11,343
Basic weighted average common shares outstanding																	25,049		24,586		23,840
Common Stock Equivalents																	475		456		643
Weighted Average Number of Shares Including Common Stock Equivalents, Diluted																	25,524		25,042		24,483
Class B Conversion																	2,587		2,587		2,615
Diluted, Class A Common Shares																	28,111		27,629		27,098
Basic, EPS																	$ 0.37	[3]	$ 0.38	[3]	$ 0.43	[3]
Diluted, EPS																	$ 0.37	[3]	$ 0.38	[3]	$ 0.42	[3]

[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 $0.37, $0.38 and $0.43 for the years ended April 30, 2014, 2013 and 2012, respectively. See Note 1 to the Consolidated Financial Statements.

[2] Quarterly amounts may not sum to full year total due to rounding.

[3] Amounts adjusted for rounding