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MINERAL, ROYALTY AND OTHER INTERESTS (Narrative) (Details)
$ in Thousands
 3 Months Ended 12 Months Ended
Jan. 26, 2017
USD ($)
Dec. 31, 2017
USD ($)
$ / item
Dec. 31, 2017
USD ($)
yr
$ / item
Dec. 31, 2016
USD ($)
$ / item
Sep. 29, 2017
USD ($)
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Proceeds from disposal of mineral, royalty and other interests     $ 3,600 $ 5,617  
Acquisition of mineral, royalty and other interests     4,409 10,806  
Impairment of mineral, royalty and other interests     $ 9,104 $ 2,507  
Chapada Mine [member] | Copper Commodity Type [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Percentage of life of mine gold or relevant commodity   4.20% 4.20%    
Bombore [Member] | Gold Commodity Type [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Proceeds from disposal of mineral, royalty and other interests $ 3,600        
Proceeds from sale of royalty interest percentage premium on original upfront payment 20.00%        
Bachelor Lake [Member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Agreement election payment amount to reduce net smelter return percentage   $ 2,000      
Other income     $ 3,000    
Bachelor Lake [Member] | Gold Commodity Type [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Percentage of life of mine gold or relevant commodity   20.00% 20.00%    
Threshold, maximum measurement weight commodity, purchased   12,000 12,000    
Net smelter return royalty percentage     1.00%    
Net smelter return royalty percentage if agreement option exercised   1.80%      
Metanor's Barry Project [member] | Gold Commodity Type [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Net smelter return royalty percentage   3.90%      
Coringa Project [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Fair value assumption used for life of mine, years | yr     5    
Description of key assumptions on which management has based determination of fair value less costs of disposal     The recoverable amount of $3.4 million was determined using a discounted cash flow model in estimating the fair value less costs of disposal. Key assumptions used in the cash flow forecast were: a 5 year mine life, a long term gold price of $1,300 and a 6% discount rate.    
Fair value assumption commodity price used | $ / item   1,300 1,300    
Discount rate used in current measurement of fair value less costs of disposal   6.00% 6.00%    
Impairment of mineral, royalty and other interests     $ 4,500    
Recoverable amount of asset or cash-generating unit   $ 3,400 3,400    
Other Royalties [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Discount rate used in current measurement of fair value less costs of disposal       4.00%  
Impairment of mineral, royalty and other interests     $ 9,104 $ 2,507  
Other Royalties [member] | Gold Commodity Type [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Fair value assumption commodity price used | $ / item       1,300  
Other Royalties Lacking Significant Progress [Member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Impairment of mineral, royalty and other interests       $ 1,400  
Other Royalties within Royalty Portfolio [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Impairment of mineral, royalty and other interests       $ 1,100  
Emigrant Springs [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Description of key assumptions on which management has based determination of fair value less costs of disposal     The recoverable amount of $0.5 million was determined using a discounted cash flow model in estimating the fair value less costs of disposal. Key assumptions used in the cash flow forecast were: a 1 - 3 year mine life, a long term gold price of $1,300 and a 4% discount rate.    
Fair value assumption commodity price used | $ / item   1,300 1,300    
Discount rate used in current measurement of fair value less costs of disposal   4.00% 4.00%    
Impairment of mineral, royalty and other interests     $ 4,600    
Recoverable amount of asset or cash-generating unit   $ 500 $ 500    
Metanor Resources Incorporated [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Fair value of shares received         $ 2,000
Bottom of range [member] | Emigrant Springs [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Fair value assumption used for life of mine, years | yr     1    
Top of range [member] | Emigrant Springs [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Fair value assumption used for life of mine, years | yr     3    
After 12,000 Ounces [member] | Bachelor Lake [Member] | Gold Commodity Type [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Net smelter return royalty percentage   3.90%      
Before 12,000 Ounces [member] | Bachelor Lake [Member] | Gold Commodity Type [member]          
Disclosure Of Property Plant And Equipment And Exploration And Evaluation [line items]          
Commodity purchase quantity per quarter   1,500