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Fair Value of financial instruments (Narrative) (Details)
$ in Millions, $ in Millions
12 Months Ended
Dec. 31, 2019
CAD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
CAD ($)
$ / ounce
Disclosure of fair value measurement of assets [line items]      
Foreign exchange contracts aggregate amount   $ 12.0  
Level 3 [Member]      
Disclosure of fair value measurement of assets [line items]      
Sensitivity analysis, variance, percentage     10.00%
Effect of variance on fair value $ 0.3   $ 0.4
Increase (decrease) in the fair value of investments     $ 6.7
Level 3 [Member] | Discounted cash flow [member]      
Disclosure of fair value measurement of assets [line items]      
Percentage of increase (decrease) on gold price 10.00% 10.00%  
Basis points increase (decrease) on discount rate     100
Base price used in the discounted cash flow model | $ / ounce     1,300
Discount rate     5.10%