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Decommissioning Liabilities (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Asset Retirement Obligation Disclosure [Line Items]    
Estimated reclamation discount rate 3.00% 2.90%
Closure cost obligations discount rate 7.40% 10.50%
Decommissioning liabilities $ 165.2 $ 134.0
Bottom of range    
Asset Retirement Obligation Disclosure [Line Items]    
Inflation rate 1.70% 1.90%
Top of range    
Asset Retirement Obligation Disclosure [Line Items]    
Inflation rate 3.60% 9.50%