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Financial Instruments and Risk Management (Gold Option Contracts) (Details)
$ in Millions
12 Months Ended
Jan. 07, 2019
USD ($)
Dec. 31, 2019
USD ($)
$ / oz
oz
Dec. 31, 2018
USD ($)
Disclosure of detailed information about hedged items [line items]      
Gains (losses) on change in fair value of derivatives $ 3.9    
Unrealized gains   $ 0.6 $ 0.4
Gold Options [Member] | Commodity price risk [member]      
Disclosure of detailed information about hedged items [line items]      
Financial assets, at fair value   0.7 0.1
Gains (losses) on change in fair value of derivatives   (5.9) (3.9)
Unrealized gains   $ 6.5 $ 0.6
Gold Options [Member] | 2018 [member] | Commodity price risk [member]      
Disclosure of detailed information about hedged items [line items]      
Ounces subject to contract | oz   70,050  
Purchase Put Options [Member] | Gold Options [Member] | 2018 [member] | Commodity price risk [member]      
Disclosure of detailed information about hedged items [line items]      
Average realized price per ounce | $ / oz   1,420  
Sold Call Option [Member] | Gold Options [Member] | 2018 [member] | Commodity price risk [member]      
Disclosure of detailed information about hedged items [line items]      
Average realized price per ounce | $ / oz   1,658