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		6 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Earnings Per Share [Abstract]
Earnings from continuing operations attributable to CMC	$ 9,781	$ 22,992	$ 41,652	$ 28,678
Basic earnings per share:
Shares outstanding for basic earnings per share (shares)	116,808,838	115,736,369	116,524,630	115,415,662
Basic earnings per share attributable to CMC: (in USD per share)	$ 0.08	$ 0.20	$ 0.36	$ 0.25
Diluted earnings per share:
Shares outstanding for basic earnings per share (shares)	116,808,838	115,736,369	116,524,630	115,415,662
Effect of dilutive securities:
Stock-based incentive/purchase plans (shares)	1,460,883	1,383,839	1,625,185	1,592,296
Shares outstanding for diluted earnings per share (shares)	118,269,721	117,120,208	118,149,815	117,007,958
Diluted earnings per share attributable to CMC: (in USD per share)	$ 0.08	$ 0.20	$ 0.35	$ 0.25