QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Aug. 31, 2016		May 31, 2016		Feb. 29, 2016		Nov. 30, 2015		Aug. 31, 2015		May 31, 2015		Feb. 28, 2015		Nov. 30, 2014		Aug. 31, 2016	Aug. 31, 2015	Aug. 31, 2014
Net sales		$ 1,208,580	[1]	$ 1,227,390	[1]	$ 1,019,697	[1]	$ 1,154,859	[1]	$ 1,411,496	[1]	$ 1,506,002	[1]	$ 1,391,117	[1]	$ 1,679,990	[1]	$ 4,610,526	$ 5,988,605	$ 6,790,438
Gross profit	[1]	168,095		175,480		134,821		157,617		157,703		192,148		147,075		179,923
Net earnings attributable to CMC		$ (131)		$ 19,328		$ 10,502		$ 25,063		$ 12,353		$ 28,709		$ 6,197		$ 32,184		$ 54,762	$ 79,443	$ 113,243
Basic EPS attributable to CMC		$ 0		$ 0.17		$ 0.09		$ 0.22		$ 0.11		$ 0.25		$ 0.05		$ 0.27		$ 0.48	$ 0.68	$ 0.96
Diluted EPS attributable to CMC		$ 0.00		$ 0.17		$ 0.09		$ 0.21		0.11		0.25		0.05		0.27		$ 0.47	$ 0.67	$ 0.95
Effect of change in accounting principle on EPS attributable to CMC
Net earnings attributable to CMC																		$ (17,857)	$ (62,191)	$ (2,308)
Basic EPS attributable to CMC										0.16		(0.24)		(0.41)		(0.04)		$ (0.15)	$ (0.54)	$ (0.02)
Diluted EPS attributable to CMC										$ 0.16		$ (0.24)		$ (0.41)		$ (0.03)		$ (0.15)	$ (0.53)	$ (0.02)

[1] Excludes divisions classified as discontinued operations. See Note 10, Businesses Held for Sale, Discontinued Operations and Dispositions.