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Royalty, Stream and Working Interests, Net - Impairments of Royalties, Streams and Working Interests (Details) - USD ($)
 1 Months Ended 12 Months Ended
Oct. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Impairments        
Impairment   $ 0 $ 67,500,000  
Carrying value   $ 3,939,200,000 3,668,300,000 $ 3,257,500,000
Net smelter royalty interest percent sold (as a percent) 1.00%      
Net smelter royalty interest held 2.50%      
Net proceeds from sale of smelter royalty interest $ 30,300,000      
Gross proceeds from sale of smelter royalty interest 36,000,000      
Carrying value of smelter royalty interest subject to buyback provision 16,200,000      
Gain on sale of royalty interest $ 14,100,000   14,100,000  
Cooke 4        
Impairments        
Impairment     67,400,000  
Recoverable amount of cash generating unit     2,100,000  
Long term gold price (in dollars per ounce)     $ 1,321  
Discount rate (as a percent)     8.00%  
Change in gold price assumption for impairment analysis (as a percent)     10.00%  
Change in discount rate assumption for impairment analysis (as a percent)     3.00%  
Change in expected cash flow timing for impairment analysis     5 years  
Exploration Assets        
Impairments        
Impairment     $ 100,000