v3.26.1
Property, plant and equipment - Sensitivity to changes in assumptions (Details) - USD ($)
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]    
Potential Reduction In Recoverable Amount Of Alloy CGU $ 27,974,000  
Dunkirk    
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]    
Carrying Value   $ 18,141,000
Excess of recoverable value over carrying value   1,896,000
Dunkirk | Discount rate    
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]    
Increase (decrease) in CGU valuation due to decrease in assumption.   11,676,000
Increase (Decrease) in CGU valuation due to increase in assumption   $ (8,911,000)
Percentage decrease   10.00%
Percentage increase   10.00%
Dunkirk | Long-term growth rate    
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]    
Increase (decrease) in CGU valuation due to decrease in assumption.   $ 1,574,000
Increase (Decrease) in CGU valuation due to increase in assumption   $ (1,661,000)
Percentage decrease   10.00%
Percentage increase   10.00%
Dunkirk | EBITDA    
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]    
Increase (decrease) in CGU valuation due to decrease in assumption.   $ (23,174,000)
Increase (Decrease) in CGU valuation due to increase in assumption   $ 23,174,000
Percentage decrease   10.00%
Percentage increase   10.00%
Alloy    
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]    
Carrying Value 53,704,000 $ 70,574,000
Amount Of Shortfall Of Recoverable Value Versus Carrying Value. 9,512,000  
Amount by which recoverable amount is lower than carrying amount.   (2,479,000)
Alloy | Discount rate    
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]    
Increase (decrease) in CGU valuation due to decrease in assumption. 11,072,000 16,334,000
Increase (Decrease) in CGU valuation due to increase in assumption $ (8,850,000) $ (12,761,000)
Percentage decrease 10.00% 10.00%
Percentage increase 10.00% 10.00%
Alloy | Long-term growth rate    
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]    
Increase (decrease) in CGU valuation due to decrease in assumption. $ 1,947,000 $ 760,000
Increase (Decrease) in CGU valuation due to increase in assumption $ (1,712,000) $ (806,000)
Percentage decrease 10.00% 10.00%
Percentage increase 10.00% 10.00%
Alloy | EBITDA    
Disclosure of information for impairment loss recognised or reversed for individual asset or cash-generating unit [line items]    
Increase (decrease) in CGU valuation due to decrease in assumption. $ (31,459,000) $ (28,191,000)
Increase (Decrease) in CGU valuation due to increase in assumption $ 31,333,000 $ 28,191,000
Percentage decrease 15.00% 10.00%
Percentage increase 15.00% 10.00%