Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Nov. 30, 2012		Aug. 31, 2012
Assets:
Nonqualified savings plan investments	$ 6,771		$ 6,667
Fair Value, Measurements, Recurring
Assets:
Derivative financial instruments	4,082		2,844
Nonqualified savings plan investments	6,771		6,667
Cash equivalents	1,002		1,002
Assets, Fair Value Disclosure, Total	11,855		10,513
Liabilities:
Derivative financial instruments	2,470		3,145
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Assets:
Nonqualified savings plan investments	6,771		6,667
Cash equivalents	1,002		1,002
Assets, Fair Value Disclosure, Total	7,773		7,669
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Assets:
Derivative financial instruments	4,082	[1]	2,844
Assets, Fair Value Disclosure, Total	4,082	[1]	2,844
Liabilities:
Derivative financial instruments	2,470	[1]	3,145
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Assets:
Derivative financial instruments
Nonqualified savings plan investments
Cash equivalents
Assets, Fair Value Disclosure, Total
Liabilities:
Derivative financial instruments

[1] Level 2 assets and liabilities include derivative financial instruments which are valued based on significant observable inputs. See note 10 Derivative Instruments for further discussion.