CONDENSED CONSOLIDATED STATEMENTS OF EARNINGS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2017	May 31, 2016
Income Statement [Abstract]
Net sales	$ 1,382,616	$ 1,227,390	$ 3,607,300	$ 3,401,946
Costs and expenses:
Cost of goods sold	1,209,195	1,051,910	3,142,697	2,934,028
Selling, general and administrative expenses	108,803	114,841	324,789	310,667
Interest expense	12,368	14,737	38,108	49,666
Loss on debt extinguishment	0	115	0	11,480
Total costs and expenses	1,330,366	1,181,603	3,505,594	3,305,841
Earnings from continuing operations before income taxes	52,250	45,787	101,706	96,105
Income taxes	12,641	10,676	25,284	24,512
Earnings from continuing operations	39,609	35,111	76,422	71,593
Loss from discontinued operations before income taxes (benefit)	(351)	(15,785)	(542)	(16,803)
Income taxes (benefit)	(8)	(2)	7	(103)
Loss from discontinued operations	(343)	(15,783)	(549)	(16,700)
Net earnings	39,266	19,328	75,873	54,893
Less net earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to CMC	$ 39,266	$ 19,328	$ 75,873	$ 54,893
Basic earnings (loss) per share attributable to CMC:
Earnings from continuing operations (in USD per share)	$ 0.34	$ 0.31	$ 0.66	$ 0.62
Earnings (loss) from discontinued operations (in USD per share)	0.00	(0.14)	0.00	(0.14)
Net earnings (in USD per share)	0.34	0.17	0.66	0.48
Diluted earnings (loss) per share attributable to CMC:
Earnings from continuing operations (in USD per share)	0.34	0.30	0.65	0.61
Earnings (loss) from discontinued operations (in USD per share)	0.00	(0.13)	0.00	(0.14)
Net earnings (in USD per share)	0.34	0.17	0.65	0.47
Cash dividends per share (in USD per share)	$ 0.12	$ 0.12	$ 0.36	$ 0.36
Average basic shares outstanding	115,886,372	114,677,109	115,574,289	115,373,736
Average diluted shares outstanding	117,205,369	115,995,515	117,087,341	116,758,716