Amortized Cost and Fair Values of Marketable Securities Classified as Available-For-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2014		Apr. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			$ 43,835
Gross Unrealized Gains			94
Gross Unrealized Losses			(14)	[1]
Estimated Fair Value	18,352	[2]	43,915	[2]
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,325		42,033
Gross Unrealized Gains	31		92
Gross Unrealized Losses	(4)	[1]	(14)	[1]
Estimated Fair Value	18,352	[2]	42,111	[2]
U.S. Treasury And Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			1,802
Gross Unrealized Gains			2
Estimated Fair Value			$ 1,804	[2]

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

[2] 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 April 30, 2014 and 2013, the Company had no investments classified as Level 3.