EARNINGS PER SHARE (Calculations of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Aug. 31, 2021	Aug. 31, 2020	Aug. 31, 2019
Earnings Per Share [Abstract]
Earnings from continuing operations	$ 412,865	$ 278,302	$ 198,779
Basic earnings per share:
Shares outstanding for basic earnings per share	120,338,357	118,921,854	117,834,558
Basic earnings per share from continuing operations attributable to CMC (USD per share)	$ 3.43	$ 2.34	$ 1.69
Diluted earnings per share:
Shares outstanding for basic earnings per share	120,338,357	118,921,854	117,834,558
Effect of dilutive securities:
Stock-based incentive/purchase plans	1,645,140	1,387,767	1,290,070
Shares outstanding for diluted earnings per share	121,983,497	120,309,621	119,124,628
Diluted earnings per share from continuing operations attributable to CMC (USD per share)	$ 3.38	$ 2.31	$ 1.67