Earnings Per Share Attributable To CMC (Calculations of the Basic and Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2014	Feb. 28, 2013
Earnings Per Share [Abstract]
Net earnings attributable to CMC	$ 11,143	$ 4,577	$ 57,062	$ 54,294
Basic earnings per share:
Shares outstanding for basic earnings per share	117,424,962	116,586,100	117,247,731	116,461,302
Basic earnings per share attributable to CMC:	$ 0.09	$ 0.04	$ 0.49	$ 0.47
Diluted earnings per share:
Shares outstanding for basic earnings per share	117,424,962	116,586,100	117,247,731	116,461,302
Effect of dilutive securities:
Share-based incentive/purchase plans	1,214,199	986,952	1,150,155	872,037
Shares outstanding for diluted earnings per share	118,639,161	117,573,052	118,397,886	117,333,339
Diluted earnings per share attributable to CMC:	$ 0.09	$ 0.04	$ 0.48	$ 0.46
Anti-dilutive shares not included above	1,175,090	2,042,017	1,175,090	2,042,017