v3.26.1
Property, plant and equipment - Impairment, disposals and pledged as security (Details) - USD ($)
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Recoverable amount of asset or cash-generating unit $ 26,858,000    
Impairment charges 27,902,000 $ 24,940,000 $ 25,768,000
Reversal of impairment (12,161,000)    
Percentage Reduction Of Recoverable Amount of Pierrefitte Emalahleni   10.00%  
Selma      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Impairment charges     21,008,000
Alloy      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Carrying value 53,704,000    
Recoverable amount of asset or cash-generating unit 44,192,000    
Impairment charges $ 9,512,000 $ 2,479,000  
Post Tax Discount Rate 10.27%    
Long-Term Growth rate 2.21% 2.30%  
Pre-tax discount rate   13.60%  
Boo      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Impairment charges $ 5,541,000   1,570,000
Cee-Dumbria      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Impairment charges 1,808,000 $ 3,646,000 3,619,000
Polokwane      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Impairment charges 372,000 12,953,000  
Puertollano      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Carrying value 22,538,000 26,870,000  
Recoverable amount of asset or cash-generating unit   21,058,000  
Impairment charges   5,862,000  
Impairment Loss Adjustments.   $ 5,812,000  
Dunkirk      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Long-Term Growth rate   2.30%  
Pre-tax discount rate   15.60%  
Monzon [member]      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Impairment charges 2,130,000    
Pierrefite [member]      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Impairment charges $ 8,539,000    
Others      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Reversal of impairment     $ (429,000)
Minimum | Alloy      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
EBITDA Margin (10.80%) (3.20%)  
Minimum | Dunkirk      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
EBITDA Margin   0.70%  
Maximum | Alloy      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
EBITDA Margin 31.90% 23.00%  
Maximum | Dunkirk      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
EBITDA Margin   19.20%  
Other financial liabilities      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Property, plant and equipment pledged as security   $ 42,277,000  
Industrial equipment | Minimum | Puertollano      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Estimate cost to dispose based on asset category 15.00%    
Industrial equipment | Maximum | Puertollano      
Disclosure of impairment loss and reversal of impairment loss [abstract]      
Estimate cost to dispose based on asset category 100.00%