Fair Value Of Financial Instruments And Long-Term Debt (Long-Term Debt At Carrying Amount) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2012	Apr. 30, 2011
Long-Term Debt At Carrying Amount [Line Items]
Long-term debt	$ 678,667	$ 679,847
Less current maturities	10,737	1,167
Long-term debt, excluding current maturities, total	667,930	678,680
Capital Lease Obligations [Member]
Long-Term Debt At Carrying Amount [Line Items]
Capital lease obligations	9,645	10,344
Number of installments	various monthly installments through 2048
Mortgage Notes Payable [Member]
Long-Term Debt At Carrying Amount [Line Items]
Long-term debt	22	503
Stated interest rate	6.00%
Number of installments	various installments through January 2013
5.72% Senior Notes [Member]
Long-Term Debt At Carrying Amount [Line Items]
Senior notes	100,000	100,000
Stated interest rate	5.72%
Number of installments	14
Debt instrument, maturity date range, start	Sep. 30, 2012
Debt instrument, maturity date range, end	Mar. 30, 2020
5.22% Senior Notes [Member]
Long-Term Debt At Carrying Amount [Line Items]
Senior notes	$ 569,000	$ 569,000
Stated interest rate	5.22%
Debt instrument, maturity date	Aug. 09, 2020
Minimum [Member] | Capital Lease Obligations [Member]
Long-Term Debt At Carrying Amount [Line Items]
Discount rate of capitalized lease obligations	5.22%
Maximum [Member] | Capital Lease Obligations [Member]
Long-Term Debt At Carrying Amount [Line Items]
Discount rate of capitalized lease obligations	7.09%