Borrowings (Narrative) (Details) (USD $)	6 Months Ended				6 Months Ended						6 Months Ended				0 Months Ended	6 Months Ended	3 Months Ended
	Oct. 31, 2012	Aug. 31, 2012	Apr. 30, 2012	Oct. 31, 2011	Oct. 31, 2012 Minimum [Member]	Oct. 31, 2012 Maximum [Member]	Oct. 31, 2012 LIBOR [Member] Minimum [Member]	Oct. 31, 2012 LIBOR [Member] Maximum [Member]	Oct. 31, 2012 PRIME [Member] Minimum [Member]	Oct. 31, 2012 PRIME [Member] Maximum [Member]	Oct. 31, 2012 Fiscal Quarters Ending April 30, October 31, And October 31 [Member]	Oct. 31, 2012 Fiscal Quarter Ending On January 31 [Member]	Oct. 31, 2012 Senior Notes, 5.500%, Due November 2022 [Member]	Oct. 25, 2012 Senior Notes, 5.500%, Due November 2022 [Member]	Nov. 26, 2012 Senior Notes, 7.875% Due January 2013 [Member]	Oct. 31, 2012 Senior Notes, 7.875% Due January 2013 [Member]	Jan. 31, 2013 Forecast [Member]
Line of Credit Facility [Line Items]
Long-term debt	$ 906,125,000		$ 409,115,000	$ 1,009,196,000										$ 500,000,000
Long-term note, interest rate													5.50%			7.875%
Senior notes, maturity date													Nov. 01, 2022			Jan. 01, 2013
Call and repayment price															623,000,000
Make-whole premium															5,800,000
Senior notes, accrued interest															17,200,000
Gain (loss) on extinguishment of debt																	(6,000,000)
Line of credit agreement period	5 years
Committed line of credit amount		$ 1,500,000,000
Annual interest rate of facility							0.75%	1.45%	0.00%	0.45%
Line of Credit Facility, Commitment Fee Percentage					0.125%	0.30%
Threshold of debt to EBITDA ratio											3.50%	3.75%
Interest coverage ratio	2.50%