Components of Investments (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2014	Apr. 30, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total debt securities	$ 16,355	$ 15,035
Marketable equity securities	7,416	9,999
Trading Securities, Total	23,771	25,034
Tax-exempt state and municipal bonds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total debt securities	15,167	13,031
Corporate bonds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total debt securities	1,188	1,486
Certificates of deposit
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total debt securities		240
Other government bonds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total debt securities		$ 278