Summary of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2013		Apr. 30, 2012
Schedule Of Marketable Securities [Line Items]
Trading	$ 95,807	[1],[2]	$ 82,176	[1],[2]
Less: current portion of marketable securities	(4,255)	[1],[2]	(7,613)	[1],[2]
Non-current marketable securities	91,552	[1],[2]	74,563	[1],[2]
Available-for-Sale	41,304	[2],[3]	53,558	[2],[3]
Less: current portion of marketable securities	(19,063)	[2],[3]	(33,323)	[2],[3]
Non-current marketable securities, Available-for-Sale	22,241	[2],[3]	20,235	[2],[3]
Total	137,111		135,734
Less: current portion of marketable securities	(23,318)		(40,936)
Non-current marketable securities	113,793		94,798
Mutual Funds
Schedule Of Marketable Securities [Line Items]
Trading	95,807	[1],[2]	82,176	[1],[2]
Total	95,807		82,176
Corporate Bonds
Schedule Of Marketable Securities [Line Items]
Available-for-Sale	41,304	[2],[3]	44,563	[2],[3]
Total	41,304		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			3,006	[2],[3]
Total			$ 3,006

[1] (1) These investments are held in trust for settlement of the Company's obligations of $96.5 million and $82.6 million as of January 31, 2013 and April 30, 2012, respectively, under the Executive Capital Accumulation Plan ("ECAP") (see Note 6 - Deferred Compensation and Retirement Plans). The fair value of marketable securities classified as trading (held in trust to satisfy obligations under the ECAP) increased by $4.6 million and decreased by $2.3 million during the nine months ended January 31, 2013 and 2012, respectively, recorded in other income (loss), net on the consolidated statements of income. The remaining activity is comprised primarily of Company and employee contributions made of $20.0 million and $1.9 million, respectively, offset by distributions of $12.9 million for the nine months ended January 31, 2013.

[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 January 31, 2013 and April 30, 2012, the Company had cash equivalents of $58.5 million and $60.5 million and restricted cash of $2.9 million and $10.0 million, respectively, classified as Level 1.

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