BUSINESS SEGMENTS (Summary of Certain Financial Information from Continuing Operations by Reportable Segment and Major Product) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	May 31, 2021	Aug. 31, 2020	May 31, 2020	May 31, 2021	May 31, 2020	Aug. 31, 2020
Segment Reporting Information [Line Items]
Net sales	$ 1,845,041		$ 1,341,683	$ 4,699,114	$ 4,067,354
Adjusted EBITDA	221,121		146,782	506,487	444,308
Total assets	4,391,075	$ 4,081,728		4,391,075		$ 4,081,728
Segments \| Continuing Operations
Segment Reporting Information [Line Items]
Net sales	1,845,041		1,341,683	4,699,114	4,067,354
Adjusted EBITDA	221,121	146,782		506,487		444,308
Total assets	4,391,075	4,081,728		4,391,075		4,081,728
Segments \| North America
Segment Reporting Information [Line Items]
Net sales	1,558,068		1,167,081	4,010,567	3,545,084
Adjusted EBITDA	207,330	159,394		534,576		486,957
Total assets	3,089,579	2,862,805		3,089,579		2,862,805
Segments \| Europe
Segment Reporting Information [Line Items]
Net sales	284,107		173,817	680,769	519,285
Adjusted EBITDA	50,005	14,270		80,582		39,080
Total assets	675,880	532,850		675,880		532,850
Segments \| Unaffiliated Customers
Segment Reporting Information [Line Items]
Net sales	1,845,041		1,341,683	4,699,114	4,067,354
Segments \| Unaffiliated Customers \| North America
Segment Reporting Information [Line Items]
Net sales	1,558,068		1,167,081	4,010,567	3,545,084
Segments \| Unaffiliated Customers \| Europe
Segment Reporting Information [Line Items]
Net sales	283,713		173,465	679,457	518,161
Segments \| Raw materials
Segment Reporting Information [Line Items]
Net sales	352,518		161,673	825,372	541,221
Segments \| Raw materials \| North America
Segment Reporting Information [Line Items]
Net sales	346,614		159,174	811,863	534,109
Segments \| Raw materials \| Europe
Segment Reporting Information [Line Items]
Net sales	5,904		2,499	13,509	7,112
Segments \| Steel Products
Segment Reporting Information [Line Items]
Net sales	841,172		552,910	2,121,967	1,708,990
Segments \| Steel Products \| North America
Segment Reporting Information [Line Items]
Net sales	626,084		420,169	1,597,942	1,298,980
Segments \| Steel Products \| Europe
Segment Reporting Information [Line Items]
Net sales	215,088		132,741	524,025	410,010
Segments \| Downstream products
Segment Reporting Information [Line Items]
Net sales	532,158		527,404	1,437,819	1,520,854
Segments \| Downstream products \| North America
Segment Reporting Information [Line Items]
Net sales	475,714		494,519	1,313,140	1,436,011
Segments \| Downstream products \| Europe
Segment Reporting Information [Line Items]
Net sales	56,444		32,885	124,679	84,843
Segments \| Other
Segment Reporting Information [Line Items]
Net sales	119,193		99,696	313,956	296,289
Segments \| Other \| North America
Segment Reporting Information [Line Items]
Net sales	109,656		93,219	287,622	275,984
Segments \| Other \| Europe
Segment Reporting Information [Line Items]
Net sales	6,277		5,340	17,244	16,196
Segments \| Corporate
Segment Reporting Information [Line Items]
Net sales	2,866			7,778
Adjusted EBITDA	(36,214)
Total assets	625,616	686,073		625,616		686,073
Segments \| Corporate \| Unaffiliated Customers
Segment Reporting Information [Line Items]
Net sales	3,260		1,137	9,090	4,109
Segments \| Corporate \| Raw materials
Segment Reporting Information [Line Items]
Net sales	0		0	0	0
Segments \| Corporate \| Steel Products
Segment Reporting Information [Line Items]
Net sales	0		0	0	0
Segments \| Corporate \| Downstream products
Segment Reporting Information [Line Items]
Net sales	0		0	0	0
Segments \| Corporate \| Other
Segment Reporting Information [Line Items]
Net sales	3,260		1,137	9,090	4,109
Segments \| Corporate and Other
Segment Reporting Information [Line Items]
Net sales			785		2,985
Adjusted EBITDA		$ (26,882)		(108,671)		$ (81,729)
Intersegment
Segment Reporting Information [Line Items]
Net sales	0		0	0	0
Intersegment \| North America
Segment Reporting Information [Line Items]
Net sales	0		0	0	0
Intersegment \| Europe
Segment Reporting Information [Line Items]
Net sales	394		352	1,312	1,124
Intersegment \| Corporate
Segment Reporting Information [Line Items]
Net sales	$ (394)		$ (352)	$ (1,312)	$ (1,124)