Credit Arrangement (Details Textual) (USD $)	12 Months Ended
	Aug. 31, 2011	Aug. 31, 2010	Aug. 31, 2009	Aug. 31, 2011 5.625% notes due November 2013 [Member]	Aug. 31, 2011 6.50% notes due July 2017 [Member]	Aug. 31, 2011 7.35% notes due August 2018 [Member]	Nov. 24, 2012 Revolving credit facility [Member]	Aug. 31, 2011 CMCZ term note [Member]
Credit Arrangements [Abstract]
Remaining borrowing capacity under revolving credit agreement	$ 400,000,000
Minimum interest coverage ratio for rolling twelve month cumulative period	250.00%
Actual interest coverage ratio	335.00%
Maximum Debt to capitalization ratio	60.00%
Actual Debt to capitalization ratio	54.00%
Interest capitalized in the cost of property, plant and equipment	800,000	4,500,000	12,600,000
Interest paid	71,400,000	80,000,000	91,200,000
Amount outstanding of commercial paper program	0	10,000,000
Amounts outstanding on revolving credit facility	0	0						43,000,000
Debt Instrument [Line Items]
Interest rate of notes due				5.625%	6.50%	7.35%
Termination date of interest rate swap				Nov. 15, 2013	Jul. 15, 2017	Aug. 15, 2018
Basis of interest rate swap transaction cost				3.03%	3.74%	3.67%
Revolving credit facility, maximum borrowing capacity							400,000,000
Notional amount of interest rate swap transactions					300,000,000	300,000,000
Uncommitted lines of commercial credit	$ 0	$ 0						$ 43,000,000