Credit Arrangements (Long-term Debt, Including the Deferred Gain from the Termination of the Interest Rate Swaps) (Details) (USD $)	6 Months Ended	12 Months Ended
	Feb. 28, 2013	Aug. 31, 2012
Debt Instrument [Line Items]
Total long-term debt including current maturities	$ 1,154,479,000	$ 1,161,325,000
Current maturities of long-term debt	204,072,000	4,252,000
Long-term debt	950,407,000	1,157,073,000
$200 million notes at 5.625% due November 2013 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	200,000,000	200,000,000
Debt instrument, interest rate, stated percentage	5.625%	5.625%
Debt instrument, maturity date	November 2013	November 2013
Weighted average interest rate	3.50%
Total long-term debt including current maturities	202,857,000	204,873,000
$400 million notes at 6.50% due July 2017 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	400,000,000	400,000,000
Debt instrument, interest rate, stated percentage	6.50%	6.50%
Debt instrument, maturity date	July 2017	July 2017
Weighted average interest rate	5.70%
Total long-term debt including current maturities	413,005,000	414,491,000
$500 million notes at 7.35% due August 2018 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	500,000,000	500,000,000
Debt instrument, interest rate, stated percentage	7.35%	7.35%
Debt instrument, maturity date	August 2018	August 2018
Weighted average interest rate	6.40%
Total long-term debt including current maturities	525,241,000	527,554,000
Other, including equipment notes [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities	$ 13,376,000	$ 14,407,000