EARNINGS PER SHARE (Calculations of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Aug. 31, 2020	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2020		Aug. 31, 2019		Aug. 31, 2018
Earnings Per Share [Abstract]
Earnings from continuing operations	$ 67,782	$ 64,169	$ 63,596	$ 82,755	$ 85,880	$ 78,551	$ 14,928	$ 19,420	$ 278,302		$ 198,779		$ 135,237
Basic earnings per share:
Shares outstanding for basic earnings per share									118,921,854		117,834,558		116,822,583
Basic earnings per share from continuing operations attributable to CMC (USD per share)	$ 0.57	$ 0.54	$ 0.53	$ 0.70	$ 0.73	$ 0.67	$ 0.13	$ 0.17	$ 2.34	[1]	$ 1.69	[1]	$ 1.16	[1]
Diluted earnings per share:
Shares outstanding for basic earnings per share									118,921,854		117,834,558		116,822,583
Effect of dilutive securities:
Stock-based incentive/purchase plans									1,387,767		1,290,070		1,323,265
Shares outstanding for diluted earnings per share									120,309,621		119,124,628		118,145,848
Diluted earnings per share from continuing operations attributable to CMC (USD per share)	$ 0.56	$ 0.53	$ 0.53	$ 0.69	$ 0.72	$ 0.66	$ 0.13	$ 0.16	$ 2.31	[1]	$ 1.67	[1]	$ 1.14	[1]

[1] Earnings Per Share ("EPS") is calculated independently for each component and may not sum to Net EPS due to rounding