Fair Value (Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2013		Aug. 31, 2012
Money market investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	$ 82,885	[1]	$ 172,462	[1]
Commodity derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	1,923	[2]	407	[2]
Liabilities, Fair Value Disclosure, Recurring	1,060	[2]	995	[2]
Foreign exchange derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	1,104	[2]	1,468	[2]
Liabilities, Fair Value Disclosure, Recurring	429	[2]	2,520	[2]
Other derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, Fair Value Disclosure, Recurring	4	[2]	32	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	82,885	[1]	172,462	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Commodity derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	1,923	[2]	407	[2]
Liabilities, Fair Value Disclosure, Recurring	1,052	[2]	993	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign exchange derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0	[2]	0	[2]
Liabilities, Fair Value Disclosure, Recurring	0	[2]	0	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, Fair Value Disclosure, Recurring	0	[2]	0	[2]
Significant Other Observable Inputs (Level 2) [Member] | Money market investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0	[1]	0	[1]
Significant Other Observable Inputs (Level 2) [Member] | Commodity derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0	[2]	0	[2]
Liabilities, Fair Value Disclosure, Recurring	8	[2]	2	[2]
Significant Other Observable Inputs (Level 2) [Member] | Foreign exchange derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	1,104	[2]	1,468	[2]
Liabilities, Fair Value Disclosure, Recurring	429	[2]	2,520	[2]
Significant Other Observable Inputs (Level 2) [Member] | Other derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, Fair Value Disclosure, Recurring	4	[2]	32	[2]
Significant Unobservable Inputs (Level 3) [Member] | Money market investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Commodity derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0	[2]	0	[2]
Liabilities, Fair Value Disclosure, Recurring	0	[2]	0	[2]
Significant Unobservable Inputs (Level 3) [Member] | Foreign exchange derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring		[2]	0	[2]
Liabilities, Fair Value Disclosure, Recurring	0	[2]	0	[2]
Significant Unobservable Inputs (Level 3) [Member] | Other derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, Fair Value Disclosure, Recurring	$ 0	[2]	$ 0	[2]

[1] Money market investments are short-term in nature, and the value is determined by broker quoted prices in active markets. The investment portfolio mix can change each period based on the Company's assessment of investment options.

[2] Derivative assets and liabilities classified as Level 1 are commodity futures contracts valued based on quoted market prices in the London Metal Exchange or the New York Mercantile Exchange. Amounts in Level 2 are based on broker quotes in the over-the-counter market. Further discussion regarding the Company's use of derivatives and the classification of the assets and liabilities is included in Note 9. Derivatives and Risk Management.