Consolidated Statements Of Operations (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2012	May 31, 2011
Income Statement [Abstract]
Net sales	$ 2,006,729	$ 2,062,683	$ 5,950,293	$ 5,619,425
Costs and expenses:
Cost of goods sold	1,822,520	1,844,120	5,410,770	5,152,042
Selling, general and administrative expenses	118,050	141,561	368,462	379,944
Interest expense	19,605	17,797	51,945	53,530
Total costs and expenses	1,960,175	2,003,478	5,831,177	5,585,516
Earnings from continuing operations before taxes	46,554	59,205	119,116	33,909
Income taxes (benefit)	7,488	14,493	(72,824)	8,688
Earnings from continuing operations	39,066	44,712	191,940	25,221
Earnings (loss) from discontinued operations before taxes	2,429	(9,046)	(22,780)	(34,707)
Income taxes (benefit)	812	(554)	(8,112)	(303)
Earnings (loss) from discontinued operations	1,617	(8,492)	(14,668)	(34,404)
Net earnings (loss)	40,683	36,220	177,272	(9,183)
Less net earnings attributable to noncontrolling interests	1	55	3	163
Net earnings (loss) attributable to CMC	$ 40,682	$ 36,165	$ 177,269	$ (9,346)
Basic earnings (loss) per share attributable to CMC:
Earnings from continuing operations	$ 0.34	$ 0.38	$ 1.65	$ 0.22
Earnings (loss) from discontinued operations	$ 0.01	$ (0.07)	$ (0.12)	$ (0.30)
Net earnings (loss)	$ 0.35	$ 0.31	$ 1.53	$ (0.08)
Diluted earnings (loss) per share attributable to CMC:
Earnings from continuing operations	$ 0.34	$ 0.38	$ 1.64	$ 0.22
Earnings (loss) from discontinued operations	$ 0.01	$ (0.07)	$ (0.12)	$ (0.30)
Net earnings (loss)	$ 0.35	$ 0.31	$ 1.52	$ (0.08)
Cash dividends per share	$ 0.12	$ 0.12	$ 0.36	$ 0.36
Average basic shares outstanding	115,946,691	115,403,374	115,726,793	114,819,792
Average diluted shares outstanding	116,934,840	116,360,755	116,742,593	116,037,430