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Financial Instruments and Risk Management (Available for Sale Financial Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Disclosure of fair value measurement of assets [line items]    
Financial assets $ 43.7 $ 22.8
Metella Royalty [Member]    
Disclosure of fair value measurement of assets [line items]    
Financial assets 13.5  
Monarch Gold [Member]    
Disclosure of fair value measurement of assets [line items]    
Financial assets 19.4  
Other Investments [Member]    
Disclosure of fair value measurement of assets [line items]    
Financial assets $ 10.8