Held to Maturity Investments Which are Not Recorded at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2013	Apr. 30, 2013
Schedule of Held-to-maturity Securities [Line Items]
Carrying value	$ 25	$ 226
Unrealized Gain		1
Unrealized Loss
Fair value	25	227
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Unrealized Loss
Tax-exempt state and municipal bonds
Schedule of Held-to-maturity Securities [Line Items]
Carrying value	25	226
Unrealized Gain		1
Unrealized Loss
Fair value	$ 25	$ 227