v3.26.1
Description of the Business and Significant Accounting Policies - Description of the Business (Details)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 19, 2026
Jun. 30, 2026
USD ($)
segment
item
Dec. 31, 2025
USD ($)
Segment Reporting Information      
Number of reportable segments | segment   4  
Redeemable noncontrolling interests | $   $ 143,259 $ 141,226
SDI Biocarbon Solutions | Steel Operations      
Segment Reporting Information      
Ownership percentage 100.00%    
United Steel Supply, LLC      
Segment Reporting Information      
Ownership percentage   95.00% 95.00%
Redeemable noncontrolling interests | $   $ 32,000 $ 30,000
Mesabi Nugget      
Segment Reporting Information      
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   2  
Ownership percentage   94.40%  
Unity Aluminum, Inc | Aluminum Operations | Mexico      
Segment Reporting Information      
Number of Satellite Recycled Aluminum Slab Centers   1  
Unity Aluminum, Inc | Aluminum Operations | Mississippi      
Segment Reporting Information      
Number of Satellite Recycled Aluminum Slab Centers   1  
Unity Aluminum, Inc | Aluminum Operations | Mississippi | Construction in Progress      
Segment Reporting Information      
Number of Satellite Recycled Aluminum Slab Centers   1