Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Aug. 31, 2013		May 31, 2013		Feb. 28, 2013		Nov. 30, 2012		Aug. 31, 2012		May 31, 2012		Feb. 29, 2012		Nov. 30, 2011		Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Quarterly Financial Data [Abstract]
Net sales	$ 1,698,861		$ 1,752,534	[1]	$ 1,688,665	[1]	$ 1,749,515	[1]	$ 1,833,026	[1]	$ 1,957,827	[1]	$ 1,918,049	[1]	$ 1,947,473	[1]	$ 6,889,575	$ 7,656,375	$ 7,666,773
Gross profit	160,788	[1]	175,519	[1]	139,365	[1]	186,665	[1]	179,438	[1]	186,490	[1]	179,058	[1]	171,641	[1]
Net earnings attributable to CMC	$ 4,057		$ 18,964		$ 4,577		$ 49,717		$ 30,215		$ 40,682		$ 28,853		$ 107,734		$ 77,315	$ 207,484	$ (129,617)
Basic EPS attributable to CMC	$ 0.03		$ 0.16		$ 0.04		$ 0.43		$ 0.26		$ 0.35		$ 0.25		$ 0.93		$ 0.66	$ 1.79	$ (1.13)
Diluted EPS attributable to CMC	$ 0.03		$ 0.16		$ 0.04		$ 0.42		$ 0.26		$ 0.35		$ 0.25		$ 0.93		$ 0.66	$ 1.78	$ (1.12)

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