QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Aug. 31, 2015		May. 31, 2015		Feb. 28, 2015		Nov. 30, 2014		Aug. 31, 2014		May. 31, 2014		Feb. 28, 2014		Nov. 30, 2013		Aug. 31, 2015	Aug. 31, 2014	Aug. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Net sales		$ 1,411,496	[1]	$ 1,506,002	[1]	$ 1,391,117	[1]	$ 1,679,990	[1]	$ 1,837,309	[1]	$ 1,738,593	[1]	$ 1,597,461	[1]	$ 1,617,075	[1]	$ 5,988,605	$ 6,790,438	$ 6,601,070
Gross profit	[1]	131,809		235,958		221,414		186,221		183,452		178,419		142,356		176,873
Net earnings attributable to CMC		$ (5,751)		$ 56,681		$ 54,451		$ 36,253		$ 34,926		$ 23,563		$ 11,143		$ 45,919		$ 141,634	$ 115,551	$ 77,315
Basic EPS attributable to CMC		$ (0.05)		$ 0.49		$ 0.47		$ 0.31		$ 0.29		$ 0.20		$ 0.09		$ 0.39		$ 1.22	$ 0.98	$ 0.66
Diluted EPS attributable to CMC		$ (0.05)		$ 0.49		$ 0.46		$ 0.30		$ 0.29		$ 0.20		$ 0.09		$ 0.39		$ 1.20	$ 0.97	$ 0.66
Pre-tax LIFO income (expense)		$ (36,500)		$ 37,100		$ 72,500		$ 6,200										$ 79,300

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