STOCKHOLDERS’ EQUITY AND EARNINGS PER SHARE ATTRIBUTABLE TO CMC (Calculations of the Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2017	May 31, 2016
Earnings Per Share [Abstract]
Earnings from continuing operations attributable to CMC	$ 39,609	$ 35,111	$ 76,422	$ 71,593
Basic earnings per share:
Shares outstanding for basic earnings per share (shares)	115,886,372	114,677,109	115,574,289	115,373,736
Basic earnings per share attributable to CMC: (in USD per share)	$ 0.34	$ 0.31	$ 0.66	$ 0.62
Diluted earnings per share:
Shares outstanding for basic earnings per share (shares)	115,886,372	114,677,109	115,574,289	115,373,736
Effect of dilutive securities:
Stock-based incentive/purchase plans (shares)	1,318,997	1,318,406	1,513,052	1,384,980
Shares outstanding for diluted earnings per share (shares)	117,205,369	115,995,515	117,087,341	116,758,716
Diluted earnings per share attributable to CMC: (in USD per share)	$ 0.34	$ 0.30	$ 0.65	$ 0.61
Anti-dilutive shares not included above (shares)	0	295,107	0	295,107