Derivative Financial Instruments (Details) (USD $)	3 Months Ended		6 Months Ended								6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010	Apr. 30, 2011	Oct. 31, 2011 6.63% Senior Notes due November 1, 2018 [Member]	Apr. 30, 2011 6.63% Senior Notes due November 1, 2018 [Member]	Oct. 31, 2011 3.50% Notes due October 15, 2021 [Member]	Oct. 18, 2011 3.50% Notes due October 15, 2021 [Member]	Apr. 30, 2011 3.50% Notes due October 15, 2021 [Member]	Oct. 31, 2011 2012 [Member]	Oct. 31, 2011 2013 through 2018 [Member]	Oct. 31, 2011 2019 [Member]	Oct. 31, 2011 Commodity contracts [Member]	Oct. 31, 2010 Commodity contracts [Member]	Oct. 31, 2011 Commodity contracts [Member]	Oct. 31, 2010 Commodity contracts [Member]	Apr. 30, 2011 Commodity contracts [Member]	Oct. 31, 2011 Commodity contracts [Member] Cash Flow Hedging [Member]	Oct. 31, 2010 Commodity contracts [Member] Cash Flow Hedging [Member]	Oct. 31, 2011 Commodity contracts [Member] Cash Flow Hedging [Member]	Oct. 31, 2010 Commodity contracts [Member] Cash Flow Hedging [Member]	Oct. 31, 2011 Interest rate contract [Member]	Apr. 30, 2011 Interest rate contract [Member]	Oct. 31, 2011 Interest rate contract [Member] Cash Flow Hedging [Member]	Oct. 31, 2010 Interest rate contract [Member] Cash Flow Hedging [Member]	Oct. 31, 2011 Interest rate contract [Member] Cash Flow Hedging [Member]	Oct. 31, 2010 Interest rate contract [Member] Cash Flow Hedging [Member]	Oct. 31, 2011 Foreign currency exchange contracts [Member]	Oct. 31, 2010 Foreign currency exchange contracts [Member]	Oct. 31, 2011 Foreign currency exchange contracts [Member]	Oct. 31, 2010 Foreign currency exchange contracts [Member]	Apr. 30, 2011 Foreign currency exchange contracts [Member]	Oct. 31, 2011 Other Current Assets [Member]	Apr. 30, 2011 Other Current Assets [Member]	Oct. 31, 2011 Other Current Assets [Member] Designated as Hedging Instrument [Member]	Apr. 30, 2011 Other Current Assets [Member] Designated as Hedging Instrument [Member]	Oct. 31, 2011 Other Current Assets [Member] Not designated as hedging instrument [Member]	Apr. 30, 2011 Other Current Assets [Member] Not designated as hedging instrument [Member]	Oct. 31, 2011 Other Current Assets [Member] Commodity contracts [Member] Designated as Hedging Instrument [Member]	Apr. 30, 2011 Other Current Assets [Member] Commodity contracts [Member] Designated as Hedging Instrument [Member]	Oct. 31, 2011 Other Current Assets [Member] Commodity contracts [Member] Not designated as hedging instrument [Member]	Apr. 30, 2011 Other Current Assets [Member] Commodity contracts [Member] Not designated as hedging instrument [Member]	Oct. 31, 2011 Other Current Assets [Member] Interest rate contract [Member] Designated as Hedging Instrument [Member]	Apr. 30, 2011 Other Current Assets [Member] Interest rate contract [Member] Designated as Hedging Instrument [Member]	Oct. 31, 2011 Other Current Assets [Member] Foreign currency exchange contracts [Member] Not designated as hedging instrument [Member]	Apr. 30, 2011 Other Current Assets [Member] Foreign currency exchange contracts [Member] Not designated as hedging instrument [Member]	Oct. 31, 2011 Other Current Liabilities [Member]	Apr. 30, 2011 Other Current Liabilities [Member]	Oct. 31, 2011 Other Current Liabilities [Member] Designated as Hedging Instrument [Member]	Apr. 30, 2011 Other Current Liabilities [Member] Designated as Hedging Instrument [Member]	Oct. 31, 2011 Other Current Liabilities [Member] Not designated as hedging instrument [Member]	Apr. 30, 2011 Other Current Liabilities [Member] Not designated as hedging instrument [Member]	Oct. 31, 2011 Other Current Liabilities [Member] Commodity contracts [Member] Designated as Hedging Instrument [Member]	Apr. 30, 2011 Other Current Liabilities [Member] Commodity contracts [Member] Designated as Hedging Instrument [Member]	Oct. 31, 2011 Other Current Liabilities [Member] Commodity contracts [Member] Not designated as hedging instrument [Member]	Apr. 30, 2011 Other Current Liabilities [Member] Commodity contracts [Member] Not designated as hedging instrument [Member]	Oct. 31, 2011 Other Current Liabilities [Member] Interest rate contract [Member] Designated as Hedging Instrument [Member]	Apr. 30, 2011 Other Current Liabilities [Member] Interest rate contract [Member] Designated as Hedging Instrument [Member]	Oct. 31, 2011 Other Current Liabilities [Member] Foreign currency exchange contracts [Member] Not designated as hedging instrument [Member]	Apr. 30, 2011 Other Current Liabilities [Member] Foreign currency exchange contracts [Member] Not designated as hedging instrument [Member]	Apr. 30, 2011 Other Noncurrent Liabilities [Member]	Apr. 30, 2011 Other Noncurrent Liabilities [Member] Designated as Hedging Instrument [Member]	Apr. 30, 2011 Other Noncurrent Liabilities [Member] Not designated as hedging instrument [Member]	Apr. 30, 2011 Other Noncurrent Liabilities [Member] Commodity contracts [Member] Designated as Hedging Instrument [Member]	Apr. 30, 2011 Other Noncurrent Liabilities [Member] Commodity contracts [Member] Not designated as hedging instrument [Member]	Apr. 30, 2011 Other Noncurrent Liabilities [Member] Interest rate contract [Member] Designated as Hedging Instrument [Member]	Apr. 30, 2011 Other Noncurrent Liabilities [Member] Foreign currency exchange contracts [Member] Not designated as hedging instrument [Member]
Fair value of derivative instruments [Line Items]
Derivatives Instruments, Assets																																		$ 4,541,000	$ 19,035,000	$ 976,000	$ 8,831,000	$ 3,565,000	$ 10,204,000	$ 976,000	$ 3,408,000	$ 3,521,000	$ 9,887,000	$ 0	$ 5,423,000	$ 44,000	$ 317,000
Derivatives Instruments, Liabilities																																																7,105,000	8,636,000	537,000	0	6,568,000	8,636,000	537,000	0	6,497,000	5,432,000	0	0	71,000	3,204,000	1,384,000	1,384,000	0	0	0	1,384,000	0
Tax impact related to deferred losses and gains on cash flow hedges included in accumulated other comprehensive (loss) income														(2,372,000)		(2,372,000)		3,430,000					(2,227,000)
Deferred pretax loss/gain included in accumulated other comprehensive income (loss/gain)														6,522,000		6,522,000		(9,430,000)					6,174,000
Cash flow hedging derivative instruments gain loss
(Losses) gains recognized in other comprehensive (loss) income (effective portion)																			(4,246,000)	4,103,000	(10,260,000)	13,034,000			(6,192,000)	0	(6,192,000)	0
(Losses) gains reclassified from accumulated other comprehensive (loss) income to earnings (effective portion)																			(416,000)	6,329,000	5,692,000	6,292,000			(18,000)	0	(18,000)	0
Change in accumulated other comprehensive (loss)income	(10,004,000)	(2,226,000)	(22,126,000)	6,742,000															(3,830,000)	(2,226,000)	(15,952,000)	6,742,000			(6,174,000)	0	(6,174,000)	0
(Losses) gains recognized in earnings (ineffective portion)																			(392,000)	203,000	(513,000)	374,000			(19,000)	0	(19,000)	0
Gains and losses recognized in cost of products sold on derivatives not designated as qualified hedging instruments
Gains (losses) recognized in cost of products sold (derivatives not designated as hedging instruments)	3,677,000	247,000	17,459,000	5,117,000										2,107,000	454,000	15,804,000	4,847,000												1,570,000	(207,000)	1,655,000	270,000
Outstanding derivative contracts
Gross contract notional amount					376,000,000									944,265,000		944,265,000		869,107,000					0	376,000,000					66,015,000		66,015,000		73,158,000
Derivative Financial Instruments (Textual) [Abstract]
Interest rate on Senior Notes						6.63%	6.63%	3.50%		3.50%
Termination loss on interest rate swap																							6,200,000		6,200,000
Deferred gain recognized over the period											2,500,000	3,300,000	1,600,000
Derivative instrument maturity														1 year		1 year													1 year		1 year
Effective portion of the hedge loss reclassified to interest expense upon termination of the swap																									300,000
Senior Notes including Unamortized Discount	750,000,000		750,000,000						750,000,000
Derivative Financial Instruments (Textual)
Cash margin accounts related to derivative instruments recognized	13,309,000		13,309,000		12,292,000
Maximum expected recognized period of deferred gain/loss in earnings			P1Y
Gain on early termination agreement	$ 23,900,000