REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 29, 2020	Feb. 28, 2019	Feb. 29, 2020	Feb. 28, 2019
Disaggregation of Revenue [Line Items]
Net sales	$ 1,340,963	$ 1,402,783	$ 2,725,671	$ 2,680,125
Steel Products
Disaggregation of Revenue [Line Items]
Net sales	1,050,836	1,075,026	2,149,785	2,015,807
Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	77,074	114,252	142,336	235,323
Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	118,646	125,836	237,212	260,032
Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	66,122	60,190	133,588	117,361
Other
Disaggregation of Revenue [Line Items]
Net sales	28,285	27,479	62,750	51,602
Americas Recycling
Disaggregation of Revenue [Line Items]
Net sales	179,535	225,888	351,686	466,069
Americas Recycling | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	140	202	255	441
Americas Recycling | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	66,040	105,253	124,342	216,907
Americas Recycling | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	112,862	120,004	226,080	248,079
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	493	429	1,009	642
Americas Mills
Disaggregation of Revenue [Line Items]
Net sales	471,367	472,795	945,559	846,466
Americas Mills | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	437,648	444,327	878,811	792,292
Americas Mills | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	10,874	8,744	17,622	17,886
Americas Mills | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	3,535	3,308	6,890	6,488
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	19,310	16,416	42,236	29,800
Americas Fabrication
Disaggregation of Revenue [Line Items]
Net sales	510,381	526,678	1,080,758	961,236
Americas Fabrication | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	441,765	462,963	941,492	837,770
Americas Fabrication | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	1	0	1	0
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	66,122	60,190	133,588	117,361
Americas Fabrication | Other
Disaggregation of Revenue [Line Items]
Net sales	2,493	3,525	5,677	6,105
International Mill
Disaggregation of Revenue [Line Items]
Net sales	179,656	174,945	344,696	401,618
International Mill | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	171,283	167,534	329,227	385,304
International Mill | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	159	255	371	530
International Mill | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	2,249	2,524	4,242	5,465
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	5,965	4,632	10,856	10,319
Corporate
Disaggregation of Revenue [Line Items]
Net sales	24	2,477	2,972	4,736
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	$ 24	$ 2,477	$ 2,972	$ 4,736