Other Financial Instruments and Fair Value Measurements (Details 1) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2012		Apr. 30, 2012
Financial assets (liabilities) measured at fair value on a recurring basis
Long-term debt	$ (2,458,408)		$ (2,443,514)
Fair value measurements recurring [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Total financial instruments measured at fair value	(2,409,597)		(2,421,293)
Fair value measurements recurring [Member] | Equity mutual funds [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	19,491	[1]	14,649	[1]
Fair value measurements recurring [Member] | Municipal obligations [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	26,383	[1]	20,392	[1]
Fair value measurements recurring [Member] | Other investments [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	681	[1]	1,132	[1]
Fair value measurements recurring [Member] | Commodity contracts - net [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Derivatives	1,426	[2]	(13,406)	[2]
Fair value measurements recurring [Member] | Foreign currency exchange contracts - net [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Derivatives	830	[2]	(546)	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair value measurements recurring [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Long-term debt	(796,272)	[3]	(777,023)	[3]
Total financial instruments measured at fair value	(775,240)		(774,031)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair value measurements recurring [Member] | Equity mutual funds [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	19,491	[1]	14,649	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair value measurements recurring [Member] | Municipal obligations [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	0	[1]	0	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair value measurements recurring [Member] | Other investments [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	681	[1]	1,132	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair value measurements recurring [Member] | Commodity contracts - net [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Derivatives	847	[2]	(12,788)	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair value measurements recurring [Member] | Foreign currency exchange contracts - net [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Derivatives	13	[2]	(1)	[2]
Significant Observable Inputs (Level 2) [Member] | Fair value measurements recurring [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Long-term debt	(1,662,136)	[3]	(1,666,491)	[3]
Total financial instruments measured at fair value	(1,634,357)		(1,647,262)
Significant Observable Inputs (Level 2) [Member] | Fair value measurements recurring [Member] | Equity mutual funds [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	0	[1]	0	[1]
Significant Observable Inputs (Level 2) [Member] | Fair value measurements recurring [Member] | Municipal obligations [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	26,383	[1]	20,392	[1]
Significant Observable Inputs (Level 2) [Member] | Fair value measurements recurring [Member] | Other investments [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	0	[1]	0	[1]
Significant Observable Inputs (Level 2) [Member] | Fair value measurements recurring [Member] | Commodity contracts - net [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Derivatives	579	[2]	(618)	[2]
Significant Observable Inputs (Level 2) [Member] | Fair value measurements recurring [Member] | Foreign currency exchange contracts - net [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Derivatives	817	[2]	(545)	[2]
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements recurring [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Long-term debt	0	[3]	0	[3]
Total financial instruments measured at fair value	0		0
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements recurring [Member] | Equity mutual funds [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements recurring [Member] | Municipal obligations [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements recurring [Member] | Other investments [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Other investments	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements recurring [Member] | Commodity contracts - net [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Derivatives	0	[2]	0	[2]
Significant Unobservable Inputs (Level 3) [Member] | Fair value measurements recurring [Member] | Foreign currency exchange contracts - net [Member]
Financial assets (liabilities) measured at fair value on a recurring basis
Derivatives	$ 0	[2]	$ 0	[2]

[1] The Company's other investments consist of funds maintained for the payment of benefits associated with nonqualified retirement plans. The funds include equity securities listed in active markets and municipal obligations valued by a third party using valuation techniques which utilize inputs that are derived principally from or corroborated by observable market data. As of October 31, 2012, the Company's municipal obligations are scheduled to mature as follows: $3,587 in 2013, $707 in 2014, $2,714 in 2015, $548 in 2016, and $18,827 in 2017 and beyond.

[2] The Company's Level 1 derivatives are valued using quoted market prices for identical instruments in active markets. The Level 2 derivatives are valued using quoted prices for similar assets or liabilites in active markets and inputs other than quoted prices that are observable for the asset or liability. For additional information, see Note 13: Derivative Financial Instruments.

[3] The Company's long-term debt is comprised of public Notes classified as Level 1 and private Senior Notes classified as Level 2. The public Notes are traded in an active secondary market and valued using quoted prices. The value of the private Senior Notes is based on the net present value of each interest and principal payment calculated, utilizing an interest rate derived from a fair market yield curve. For additional information, see Note 9: Debt and Financing Arrangements.