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Description of the Business and Significant Accounting Policies - Description of the Business (Details) $ in Thousands |  | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Apr. 01, 2025 | Jun. 30, 2025 USD ($) item segment | Dec. 31, 2024 USD ($)
Segment Reporting Information |  |  |
Number of reportable segments | segment |  | 4 |
Redeemable noncontrolling interests |  | $ 141,226 | $ 171,212
United Steel Supply, LLC |  |  |
Segment Reporting Information |  |  |
Acquisition of interest (as a percent) | 5.00% |  |
Percentage of remaining voting interest to be acquired | 5.00% |  |
United Steel Supply, LLC |  |  |
Segment Reporting Information |  |  |
Noncontrolling interest, ownership percentage | 95.00% | 95.00% | 90.00%
Redeemable noncontrolling interests |  | $ 30,000 | $ 60,000
SDI Biocarbon Solutions | Steel Operations |  |  |
Segment Reporting Information |  |  |
Noncontrolling interest, ownership percentage |  | 75.00% |
Mesabi Nugget |  |  |
Segment Reporting Information |  |  |
Noncontrolling interest, ownership percentage |  | 86.00% | 86.00%
Redeemable noncontrolling interests |  | $ 111,200 | $ 111,200
Unity Aluminum, Inc | Aluminum Operations |  |  |
Segment Reporting Information |  |  |
Number Of Satellite Recycled Aluminum Slab Centers | item |  | 2 |
Noncontrolling interest, ownership percentage |  | 94.40% |

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