Summary of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013		Apr. 30, 2012
Schedule Of Marketable Securities [Line Items]
Trading	$ 98,001	[1],[2]	$ 82,176	[1],[2]
Less: current portion of marketable securities	(4,537)	[1],[2]	(7,613)	[1],[2]
Non-current marketable securities	93,464	[1],[2]	74,563	[1],[2]
Available-for-Sale	43,915	[2],[3]	53,558	[2],[3]
Less: current portion of marketable securities	(15,810)	[2],[3]	(33,323)	[2],[3]
Non-current marketable securities	28,105	[2],[3]	20,235	[2],[3]
Total	141,916		135,734
Less: current portion of marketable securities	(20,347)		(40,936)
Non-current marketable securities	121,569		94,798
Mutual Funds
Schedule Of Marketable Securities [Line Items]
Trading	98,001	[1],[2]	82,176	[1],[2]
Total	98,001		82,176
Corporate Bonds
Schedule Of Marketable Securities [Line Items]
Available-for-Sale	42,111	[2],[3]	44,563	[2],[3]
Total	42,111		44,563
Commercial Paper
Schedule Of Marketable Securities [Line Items]
Available-for-Sale			5,989	[2],[3]
Total			5,989
U.S. Treasury And Agency Securities
Schedule Of Marketable Securities [Line Items]
Available-for-Sale	1,804	[2],[3]	3,006	[2],[3]
Total	$ 1,804		$ 3,006

[1] These investments are held in trust for settlement of the Company's obligations of $99.2 million and $82.6 million as of April 30, 2013 and 2012, respectively, under the Executive Capital Accumulation Plan (see Note 6 - Deferred Compensation and Retirement Plans).

[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, 2013 and 2012, the Company had cash equivalents of $93.6 million and $60.5 million, and restricted cash of $2.9 million and $10.0 million, respectively, classified as Level 1. As of April 30, 2013 and 2012, the Company had no investments classified as Level 3.

[3] These securities represent excess cash available for general corporate purposes invested, under our investment policy, with a professional money manager.