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Asset retirement obligation - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Long-Lived Assets Held-for-sale [Line Items]          
Change in estimates $ 1,100 $ 2,700 $ 6,871 $ 2,700 $ 2,675
Estimated undiscounted cash flows 358,600   358,600    
Estimated cash flows expected to be incurred, year one $ 5,300   $ 5,300    
Inflation Rate          
Long-Lived Assets Held-for-sale [Line Items]          
Asset retirement obligation, measurement input 3.41%   3.41%    
Risk free rate          
Long-Lived Assets Held-for-sale [Line Items]          
Asset retirement obligation, measurement input 10.81%   10.81%