REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Nov. 30, 2019	Nov. 30, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 1,384,708	$ 1,277,342
Steel Products
Disaggregation of Revenue [Line Items]
Net sales	1,098,949	940,781
Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	65,262	121,071
Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	118,566	134,196
Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	67,466	57,171
Other
Disaggregation of Revenue [Line Items]
Net sales	34,465	24,123
Americas Recycling
Disaggregation of Revenue [Line Items]
Net sales	172,151	240,181
Americas Recycling | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	115	239
Americas Recycling | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	58,302	111,654
Americas Recycling | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	113,218	128,075
Americas Recycling | Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	0	0
Americas Recycling | Other
Disaggregation of Revenue [Line Items]
Net sales	516	213
Americas Mills
Disaggregation of Revenue [Line Items]
Net sales	474,192	373,671
Americas Mills | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	441,163	347,965
Americas Mills | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	6,748	9,142
Americas Mills | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	3,355	3,180
Americas Mills | Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	0	0
Americas Mills | Other
Disaggregation of Revenue [Line Items]
Net sales	22,926	13,384
Americas Fabrication
Disaggregation of Revenue [Line Items]
Net sales	570,377	434,558
Americas Fabrication | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	499,727	374,807
Americas Fabrication | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	0	0
Americas Fabrication | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	0	0
Americas Fabrication | Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	67,466	57,171
Americas Fabrication | Other
Disaggregation of Revenue [Line Items]
Net sales	3,184	2,580
International Mill
Disaggregation of Revenue [Line Items]
Net sales	165,040	226,673
International Mill | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	157,944	217,770
International Mill | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	212	275
International Mill | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	1,993	2,941
International Mill | Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	0	0
International Mill | Other
Disaggregation of Revenue [Line Items]
Net sales	4,891	5,687
Corporate
Disaggregation of Revenue [Line Items]
Net sales	2,948	2,259
Corporate | Steel Products
Disaggregation of Revenue [Line Items]
Net sales	0	0
Corporate | Ferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	0	0
Corporate | Nonferrous Scrap
Disaggregation of Revenue [Line Items]
Net sales	0	0
Corporate | Construction Materials
Disaggregation of Revenue [Line Items]
Net sales	0	0
Corporate | Other
Disaggregation of Revenue [Line Items]
Net sales	$ 2,948	$ 2,259