Credit Arrangements (Long-term Debt, Including the Deferred Gain from the Termination of the Interest Rate Swaps) (Details) (USD $)	9 Months Ended			1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended
	May 31, 2013	May 31, 2012	Aug. 31, 2012	May 31, 2013 $200 million notes at 5.625% due November 2013 [Member]	May 31, 2013 $200 million notes at 5.625% due November 2013 [Member]	May 31, 2013 $200 million notes at 5.625% due November 2013 [Member]	Aug. 31, 2012 $200 million notes at 5.625% due November 2013 [Member]	May 31, 2013 $400 million notes at 6.50% due July 2017 [Member]	Aug. 31, 2012 $400 million notes at 6.50% due July 2017 [Member]	May 31, 2013 $500 million notes at 7.35% due August 2018 [Member]	Aug. 31, 2012 $500 million notes at 7.35% due August 2018 [Member]	May 31, 2013 $330 million notes at 4.875% due May 2023 [Member]	Aug. 31, 2012 $330 million notes at 4.875% due May 2023 [Member]	May 31, 2013 Other, including equipment notes [Member]	Aug. 31, 2012 Other, including equipment notes [Member]
Debt Instrument [Line Items]
Loss on debt extinguishment	$ 1,502,000	$ 0		$ 1,500,000	$ 1,502,000
Debt instrument, face amount				200,000,000	200,000,000	200,000,000	200,000,000	400,000,000	400,000,000	500,000,000	500,000,000	330,000,000
Debt instrument, interest rate, stated percentage				5.625%	5.625%	5.625%	5.625%	6.50%	6.50%	7.35%	7.35%	4.875%
Debt instrument, maturity date						November 2013	November 2013	July 2017	July 2017	August 2018	August 2018
Weighted average interest rate				2.80%	2.80%	2.80%		5.70%		6.40%		4.90%
Total long-term debt including current maturities	1,421,743,000		1,161,325,000	141,886,000	141,886,000	141,886,000	204,873,000	412,261,000	414,491,000	524,086,000	527,554,000	330,000,000	0	13,510,000	14,407,000
Current maturities of long-term debt	144,162,000		4,252,000
Long-term debt	$ 1,277,581,000		$ 1,157,073,000