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
	Nov. 30, 2013	Nov. 30, 2012
Earnings Per Share [Abstract]
Net earnings attributable to CMC	$ 45,919	$ 49,717
Basic earnings per share:
Shares outstanding for basic earnings per share	117,070,499	116,336,504
Basic earnings per share attributable to CMC:	$ 0.39	$ 0.43
Diluted earnings per share:
Shares outstanding for basic earnings per share	117,070,499	116,336,504
Effect of dilutive securities:
Share-based incentive/purchase plans	1,086,112	757,123
Shares outstanding for diluted earnings per share	118,156,611	117,093,627
Diluted earnings per share attributable to CMC:	$ 0.39	$ 0.42
Anti-dilutive shares not included above	1,364,036	2,945,188