REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2020	May 31, 2019
Disaggregation of Revenue [Line Items]
Net sales	$ 1,341,683	$ 1,605,872	$ 4,067,354	$ 4,285,997
Steel Products
Disaggregation of Revenue [Line Items]
Net sales	1,080,518	1,256,266	3,230,303	3,272,073
Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	72,494	115,847	214,830	351,170
Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	89,179	128,873	326,391	388,905
Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	72,637	71,228	206,225	188,589
Other
Disaggregation of Revenue [Line Items]
Net sales	26,855	33,658	89,605	85,260
Americas Recycling
Disaggregation of Revenue [Line Items]
Net sales	148,021	228,786	499,707	694,855
Americas Recycling | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	204	238	459	679
Americas Recycling | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	63,735	106,404	188,077	323,311
Americas Recycling | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	83,650	121,581	309,730	369,660
Americas Recycling | Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Americas Recycling | Other
Disaggregation of Revenue [Line Items]
Net sales	432	563	1,441	1,205
Americas Mills
Disaggregation of Revenue [Line Items]
Net sales	451,278	536,035	1,396,837	1,382,501
Americas Mills | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	420,169	501,925	1,298,980	1,294,217
Americas Mills | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	8,698	8,916	26,320	26,802
Americas Mills | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	3,091	4,080	9,981	10,568
Americas Mills | Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Americas Mills | Other
Disaggregation of Revenue [Line Items]
Net sales	19,320	21,114	61,556	50,914
Americas Fabrication
Disaggregation of Revenue [Line Items]
Net sales	567,782	629,510	1,648,540	1,590,746
Americas Fabrication | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	494,519	554,672	1,436,011	1,392,442
Americas Fabrication | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	0	2	1	2
Americas Fabrication | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Americas Fabrication | Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	72,637	71,228	206,225	188,589
Americas Fabrication | Other
Disaggregation of Revenue [Line Items]
Net sales	626	3,608	6,303	9,713
International Mill
Disaggregation of Revenue [Line Items]
Net sales	173,465	209,022	518,161	610,640
International Mill | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	165,626	199,431	494,853	584,735
International Mill | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	61	525	432	1,055
International Mill | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	2,438	3,212	6,680	8,677
International Mill | Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
International Mill | Other
Disaggregation of Revenue [Line Items]
Net sales	5,340	5,854	16,196	16,173
Corporate
Disaggregation of Revenue [Line Items]
Net sales	1,137	2,519	4,109	7,255
Corporate | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Corporate | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Corporate | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Corporate | Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Corporate | Other
Disaggregation of Revenue [Line Items]
Net sales	$ 1,137	$ 2,519	$ 4,109	$ 7,255