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Decommissioning Liabilities (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Asset Retirement Obligation Disclosure [Line Items]    
Estimated reclamation discount rate 1.80% 1.20%
Closure cost obligations discount rate 10.50% 10.50%
Provision for decommissioning, restoration and rehabilitation costs $ 114.9  
Reclamation expenses $ 1.2 $ 3.5
Bottom of range [member]    
Asset Retirement Obligation Disclosure [Line Items]    
Inflation rate 1.90% 1.50%
Top of range [member]    
Asset Retirement Obligation Disclosure [Line Items]    
Inflation rate 9.50% 9.50%
Provision for decommissioning, restoration and rehabilitation costs [member]    
Asset Retirement Obligation Disclosure [Line Items]    
Asset retirement obligation, undiscounted value   $ 76.6
Reclamation expenses $ 1.2