Quarterly Financial Data (Unaudited) Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Aug. 31, 2012		May 31, 2012		Feb. 29, 2012		Nov. 30, 2011		Aug. 31, 2011		May 31, 2011		Feb. 28, 2011		Nov. 30, 2010		Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Quarterly Financial Data [Abstract]
Net sales	$ 1,878,147	[1]	$ 2,006,729	[1]	$ 1,956,744	[1]	$ 1,986,820	[1]	$ 2,243,920	[1]	$ 2,062,683	[1]	$ 1,781,650	[1]	$ 1,775,092	[1]	$ 7,828,440	$ 7,863,345	$ 6,276,928
Gross profit	179,979	[1]	184,209	[1]	182,778	[1]	172,536	[1]	182,288	[1]	218,563	[1]	88,603	[1]	160,217	[1]
Net earnings (loss) attributable to CMC	$ 30,215		$ 40,682		$ 28,853		$ 107,734		$ (120,271)		$ 36,165		$ (46,162)		$ 651		$ 207,484	$ (129,617)	$ (205,344)
Basic EPS (loss) attributable to CMC	$ 0.26		$ 0.35		$ 0.25		$ 0.93		$ (1.04)		$ 0.31		$ (0.40)		$ 0.01		$ 1.79	$ (1.13)	$ (1.81)
Diluted EPS (loss) attributable to CMC	$ 0.26		$ 0.35		$ 0.25		$ 0.93		$ (1.04)		$ 0.31		$ (0.40)		$ 0.01		$ 1.78	$ (1.12)	$ (1.81)

[1] *Excludes divisions classified as discontinued operations. See Note 9, Discontinued Operations.