Consolidated Statements Of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Income Statement [Abstract]
Net sales	$ 7,828,440	$ 7,863,345	$ 6,276,928
Costs and expenses:
Cost of goods sold	7,108,938	7,213,674	5,851,373
Selling, general and administrative expenses	486,606	516,778	508,997
Impairment of assets	607	24,466	3,766
Interest expense	69,496	69,821	74,181
Total costs and expenses	7,665,647	7,824,739	6,438,317
Earnings (loss) from continuing operations before taxes	162,793	38,606	(161,389)
Income taxes (benefit)	(46,190)	19,328	(61,942)
Earnings (loss) from continuing operations	208,983	19,278	(99,447)
Loss from discontinued operations before taxes	(9,912)	(151,670)	(102,979)
Income taxes (benefit)	(8,419)	(2,988)	2,682
Loss from discontinued operations	(1,493)	(148,682)	(105,661)
Net earnings (loss)	207,490	(129,404)	(205,108)
Less net earnings attributable to noncontrolling interests	6	213	236
Net earnings (loss) attributable to CMC	$ 207,484	$ (129,617)	$ (205,344)
Basic earnings (loss) per share attributable to CMC:
Earnings (loss) from continuing operations	$ 1.80	$ 0.16	$ (0.88)
Loss from discontinued operations	$ (0.01)	$ (1.29)	$ (0.93)
Net earnings (loss)	$ 1.79	$ (1.13)	$ (1.81)
Diluted earnings (loss) per share attributable to CMC:
Earnings (loss) from continuing operations	$ 1.79	$ 0.16	$ (0.88)
Loss from discontinued operations	$ (0.01)	$ (1.28)	$ (0.93)
Net earnings (loss)	$ 1.78	$ (1.12)	$ (1.81)