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, 2015	May. 31, 2014	May. 31, 2015	May. 31, 2014
Earnings Per Share [Abstract]
Earnings from continuing operations attributable to CMC	$ 67,128	$ 24,468	$ 167,181	$ 71,422
Basic earnings per share:
Shares outstanding for basic earnings per share (shares)	115,742,534	117,705,133	116,807,469	117,400,198
Basic earnings per share attributable to CMC: (in USD per share)	$ 0.58	$ 0.21	$ 1.43	$ 0.61
Diluted earnings per share:
Shares outstanding for basic earnings per share (shares)	115,742,534	117,705,133	116,807,469	117,400,198
Effect of dilutive securities:
Stock-based incentive/purchase plans (shares)	1,016,681	1,064,542	1,063,759	1,121,618
Shares outstanding for diluted earnings per share (shares)	116,759,215	118,769,675	117,871,228	118,521,816
Diluted earnings per share attributable to CMC: (in USD per share)	$ 0.58	$ 0.21	$ 1.42	$ 0.60
Anti-dilutive shares not included above (shares)	378,006	1,248,330	245,542	1,248,330