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CHANGES IN BUSINESS (Details) $ in Millions		1 Months Ended	3 Months Ended	12 Months Ended
	Nov. 05, 2018 USD ($) fabrication_facility mini_mill	Oct. 31, 2019 USD ($)	May 31, 2018 USD ($)	Aug. 31, 2020 USD ($) location mini_mill	Aug. 31, 2018 USD ($)
Business Combinations [Abstract]
Number of rebar fabrication facilities acquired | fabrication_facility	33
Number of electric arc furnace mini mills | mini_mill	4			7
Cash purchase price	$ 701.2
Net sales of acquired business				$ 1,400.0
Net earnings of acquired business				132.7
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Facility closure costs		$ 9.8		$ 6.2
Number of facilities idled | location				6
Severance costs					$ 6.7
Structural Steel Fabrication Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of business			$ 20.3
Nonrecurring impairment charge			$ 13.7
Australian Steel Trading Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Currency translation gain (loss)					2.1
Pre-tax gain (loss)					$ 5.3

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