Long-Term Debt (Narrative) (Details) (USD $)	12 Months Ended				12 Months Ended		12 Months Ended					1 Months Ended			1 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012	Aug. 31, 2012	Apr. 30, 2014 Senior Notes, 5.500%, Due November 2022	Oct. 25, 2012 Senior Notes, 5.500%, Due November 2022	Apr. 30, 2014 Fiscal Quarter Ending April Thirty, July Thirty One, and October Thirty One [Member]	Apr. 30, 2014 Fiscal Quarter Ending January Thirty One [Member]	Apr. 30, 2014 Senior Notes, 7.875%, Due January 2013	Apr. 30, 2014 Senior Notes, 5.125%, Due October 2014	Apr. 30, 2014 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, 2014 FHLB
Debt Instrument [Line Items]
Long-term Debt	$ 906,474,000	$ 906,680,000				$ 500,000,000
Interest rate						5.50%							1.45%	0.45%		0.75%	0.00%
Proceeds from Issuance of Long-term Debt	0	497,185,000	0
Senior Notes, maturity date	Jun. 01, 2012								Jan. 15, 2013	Oct. 30, 2014
Maximum funding by facility				1,500,000,000
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 obligation, due over the next 9 years	8,980,000	9,702,000
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	400,600,000
Payments to retire debt in 2014	800,000
Payments to retire debt in 2015	800,000
Payments to retire debt in 2016	1,000,000
Payments to retire debt in 2017	1,000,000
Payments to retire debt beyond 2017	502,300,000
Amount of advanced capacity																		190,600,000
Available-for-sale securities eligible to serve as collateral	$ 203,900,000