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CHANGES IN BUSINESS - Additional Information (Details) t in Millions, $ in Millions |  | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Dec. 29, 2017 USD ($) fabrication_facility t | May 31, 2018 USD ($) | May 31, 2018 USD ($) | Aug. 31, 2017 USD ($)
Business Acquisition [Line Items] |  |  |  |
Annual melt capacity | t | 7.2 |  |  |
U.S. Rebar Steel Mill and Fabrication Assets |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Cash purchase price of acquisition | $ 600.0 |  |  |
Number of rebar fabrication facilities acquired | fabrication_facility | 33 |  |  |
Annual melt capacity | t | 2.7 |  |  |
Structural Steel Fabrication Operations |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Non-recurring impairment charge |  | $ 0.9 | $ 13.0 |
Australian Steel Trading Business |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Loss on disposal of certain assets and liabilities |  |  | $ 5.3 |
Impairment charges related to accumulated foreign currency translation |  |  |  | $ 4.2

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