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, 2018	May 31, 2017	May 31, 2018	May 31, 2017
Earnings Per Share [Abstract]
Earnings from continuing operations	$ 42,325	$ 31,567	$ 83,977	$ 60,245
Basic earnings per share:
Shares outstanding for basic earnings per share (shares)	117,111,799	115,886,372	116,722,504	115,574,289
Basic earnings per share attributable to CMC: (in USD per share)	$ 0.36	$ 0.27	$ 0.72	$ 0.52
Diluted earnings per share:
Shares outstanding for basic earnings per share (shares)	117,111,799	115,886,372	116,722,504	115,574,289
Effect of dilutive securities:
Stock-based incentive/purchase plans (shares)	1,142,992	1,318,997	1,328,360	1,513,052
Shares outstanding for diluted earnings per share (shares)	118,254,791	117,205,369	118,050,864	117,087,341
Diluted earnings per share attributable to CMC: (in USD per share)	$ 0.36	$ 0.27	$ 0.71	$ 0.51