Marketable Securities (Narrative) (Detail) (USD $)	12 Months Ended
	Apr. 30, 2012		Apr. 30, 2011		Apr. 30, 2010
Schedule Of Marketable Securities [Line Items]
Obligations for which assets are held in trust	$ 82,600,000		$ 72,100,000
Gross unrealized gains	1,013,000		7,599,000		11,137,000
Cash equivalents, including restricted cash	70,600,000		120,800,000
Available for sale marketable securities, maturities period, minimum, in months	One
Available for sale marketable securities, maturities period, maximum, in years	2.8
Trading securities	82,176,000	[1],[2]	71,363,000	[1],[2]
Marketable Securities [Member]
Schedule Of Marketable Securities [Line Items]
Gross unrealized gains	3,500,000		6,800,000
Gross unrealized losses	$ 400,000		$ 100,000

[1] These investments are held in trust for settlement of the Company's obligations of $82.6 million and $72.1 million as of April 30, 2012 and 2011, respectively, under the Executive Capital Accumulation Plan (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 $1.1 million and $7.6 million during fiscal 2012 and fiscal 2011, respectively, recorded in other (loss) income, net on the consolidated statements of income.

[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, 2012 and 2011, the Company had cash equivalents, including restricted cash of $70.6 million and $120.8 million, respectively, also classified as Level 1.