Amortized Cost and Fair Values of Marketable Securities Classified as Available-For-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2014		Apr. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	$ 16,296	[1]	$ 18,352	[1]
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,278		18,325
Gross Unrealized Gains	23		31
Gross Unrealized Losses	(5)	[2]	(4)	[2]
Estimated Fair Value	$ 16,296	[1]	$ 18,352	[1]

[1] The Company's financial assets measured at fair value on a recurring basis include trading securities classified as Level 1 and available-for-sale securities classified as Level 2. As of July 31, 2014 and April 30, 2014, the Company had no investments classified as Level 3.

[2] There are no marketable securities that have been in a continuous unrealized loss position for 12 months or more.