Derivative Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2012	Apr. 30, 2012
Commodity contracts [Member]
Outstanding derivative contracts
Gross contract notional amount	$ 926,765	$ 983,381
Foreign currency exchange contracts [Member]
Outstanding derivative contracts
Gross contract notional amount	$ 121,398	$ 94,424

Aggregate notional amount of all derivatives. The notional amount relates to a number of currency units, shares, bushels, pounds, or other units specified in a derivative instrument.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

Name:	us-gaap_NotionalAmountOfDerivatives
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant