ACCOUNTING POLICIES - Changes to Accounting Method (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 29, 2016	Feb. 28, 2015	Feb. 29, 2016	Feb. 28, 2015	Aug. 31, 2015
Condensed Consolidated Statement of Earnings for the quarter and YTD period:
Cost of goods sold	$ 884,876	$ 1,244,042	$ 1,882,118	$ 2,744,109
Income taxes	2,064	4,756	13,836	17,974
Earnings from continuing operations	$ 10,849	13,465	36,482	47,730
Net earnings attributable to CMC		$ 6,197	$ 35,565	$ 38,381
Basic earnings per share attributable to CMC:
Earnings from continuing operations (in USD per share)	$ 0.09	$ 0.12	$ 0.32	$ 0.41
Net earnings (in USD per share)	0.09	0.06	0.31	0.33
Earnings Per Share, Diluted, Other Disclosures [Abstract]
Earnings from continuing operations (in USD per share)	0.09	0.11	0.31	0.40
Net earnings (in USD per share)	$ 0.09	$ 0.05	$ 0.30	$ 0.32
Condensed Consolidated Balance Sheet as of August 31, 2015:
Inventories, net	$ 753,695		$ 753,695		$ 880,484
Current deferred tax assets	0		0		3,310
Accrued expenses and other payables	210,670		210,670		290,677
Retained earnings	1,381,294		1,381,294		1,373,568
Condensed Consolidated Statement of Cash Flows for the six months ended February 28, 2015:
Net earnings	10,502	$ 6,197	35,565	$ 38,381
Deferred income taxes			(4,614)	(8,946)
Inventories working capital change			111,544	(174,990)
Accounts payable, accrued expenses and other payables working capital change			(115,002)	(159,978)
As Originally Reported
Condensed Consolidated Statement of Earnings for the quarter and YTD period:
Cost of goods sold		1,169,703		2,663,472
Income taxes		30,841		46,288
Earnings from continuing operations	$ 27,625	61,719	$ 65,721	100,053
Net earnings attributable to CMC		$ 54,451		$ 90,704
Basic earnings per share attributable to CMC:
Earnings from continuing operations (in USD per share)	$ 0.24	$ 0.53	$ 0.57	$ 0.85
Net earnings (in USD per share)	0.24	0.47	0.56	0.77
Earnings Per Share, Diluted, Other Disclosures [Abstract]
Earnings from continuing operations (in USD per share)	0.23	0.52	0.56	0.85
Net earnings (in USD per share)	$ 0.23	$ 0.46	$ 0.55	$ 0.77
Condensed Consolidated Balance Sheet as of August 31, 2015:
Inventories, net					781,371
Current deferred tax assets					29,137
Accrued expenses and other payables					279,415
Retained earnings					1,311,544
Condensed Consolidated Statement of Cash Flows for the six months ended February 28, 2015:
Net earnings				$ 90,704
Deferred income taxes				20,401
Inventories working capital change				(252,430)
Accounts payable, accrued expenses and other payables working capital change				(160,628)
Effect of Change
Condensed Consolidated Statement of Earnings for the quarter and YTD period:
Cost of goods sold		$ 74,339		80,637
Income taxes		(26,085)		(28,314)
Earnings from continuing operations	$ (16,776)	(48,254)	$ (29,239)	(52,323)
Net earnings attributable to CMC		$ (48,254)		$ (52,323)
Basic earnings per share attributable to CMC:
Earnings from continuing operations (in USD per share)	$ (0.15)	$ (0.41)	$ (0.25)	$ (0.44)
Net earnings (in USD per share)	(0.15)	(0.41)	(0.25)	(0.44)
Earnings Per Share, Diluted, Other Disclosures [Abstract]
Earnings from continuing operations (in USD per share)	(0.14)	(0.41)	(0.25)	(0.45)
Net earnings (in USD per share)	$ (0.14)	$ (0.41)	$ (0.25)	$ (0.45)
Condensed Consolidated Balance Sheet as of August 31, 2015:
Inventories, net					99,113
Current deferred tax assets					(25,827)
Accrued expenses and other payables					11,262
Retained earnings					$ 62,024
Condensed Consolidated Statement of Cash Flows for the six months ended February 28, 2015:
Net earnings				$ (52,323)
Deferred income taxes				(29,347)
Inventories working capital change				77,440
Accounts payable, accrued expenses and other payables working capital change				$ 650