Components of Investments (Detail) - USD ($) $ in Thousands	Apr. 30, 2015	Apr. 30, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total debt securities	$ 22,269	$ 16,355
Marketable equity securities	8,471	7,416
Trading Securities, Total	30,740	23,771
Tax-exempt state and municipal bonds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total debt securities	21,555	15,167
Corporate bonds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total debt securities	$ 714	$ 1,188