Long-Term Debt (Narrative) (Details) (USD $)	12 Months Ended				0 Months Ended	12 Months Ended			0 Months Ended	12 Months Ended			1 Months Ended			1 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011	Aug. 31, 2012	Oct. 25, 2012 Senior Notes, 5.500%, Due November 2022	Apr. 30, 2013 Senior Notes, 5.500%, Due November 2022	Apr. 30, 2013 Fiscal Quarter Ending April Thirty, July Thirty One, and October Thirty One [Member]	Apr. 30, 2013 Fiscal Quarter Ending January Thirty One [Member]	Nov. 26, 2012 Senior Notes, 7.875%, Due January 2013	Apr. 30, 2013 Senior Notes, 7.875%, Due January 2013	Apr. 30, 2013 Senior Notes, 5.125%, Due October 2014	Apr. 30, 2013 Senior Notes 6 3/4% Due In November 2004	Aug. 31, 2012 Maximum	Aug. 31, 2012 Maximum LIBOR	Aug. 31, 2012 Maximum PRIME	Aug. 31, 2012 Minimum	Aug. 31, 2012 Minimum LIBOR	Aug. 31, 2012 Minimum PRIME	Apr. 30, 2013 FHLB
Debt Instrument [Line Items]
Long-term Debt	$ 906,680,000	$ 1,040,549,000			$ 500,000,000				$ 600,000,000
Interest rate					5.50%
Proceeds from Issuance of Long-term Debt	497,185,000	0	0		497,200,000
Senior Notes, maturity date	Jun. 01, 2012					Nov. 01, 2022				Jan. 15, 2013	Oct. 30, 2014
Debt Instrument Call And Repayment Price									623,000,000
Debt Instrument, Make Whole Premium									5,800,000
Debt Instrument, Increase, Accrued Interest									17,200,000
Maximum funding by facility				1,500,000,000
Annual interest rate of facility														1.45%	0.45%		0.75%	0.00%
Senior Notes, issued											400,000,000
Senior Notes, interest rate						5.50%				7.875%	5.125%
Credit facility repayment, interest rate												6.75%
Capital lease obligations	9,702,000	10,393,000
Capital lease obligation (in years)	10 years
Percentage of annual facility fee													0.30%			0.125%
Threshold of Debt to EBITDA Ratio							3.50	3.75
Interest Coverage Ratio	2.50
Payments to retire debt in 2013	700,000
Payments to retire debt in 2014	400,400,000
Payments to retire debt in 2015	800,000
Payments to retire debt in 2016	800,000
Payments to retire debt in 2017	1,000,000
Payments to retire debt beyond 2017	503,000,000
Amount of advanced capacity																			436,200,000
Mortgage loans held for investment eligible to serve as collateral	252,500,000
Available-for-sale securities eligible to serve as collateral	$ 264,000,000