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OTHER ASSETS - Narrative (Details)
oz in Millions
 8 Months Ended 12 Months Ended
May 02, 2017
USD ($)
shares
Nov. 01, 2016
USD ($)
Oct. 31, 2016
USD ($)
oz
shares
Dec. 31, 2017
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Other Assets1 [Abstract]            
Cash and security deposits from close down and restoration provisions       $ 1,895,000 $ 1,895,000 $ 1,877,000
Parral properties            
Disposal Groups, Including Discontinued Operations 1 [Line Items]            
Sale of assets, shares received as consideration | shares     1,198,083      
Sale of assets, value of equity received as consideration     $ 5,272,000      
Sale of assets, proceeds from right to receive equity     $ 200,000      
Sale of assets, silver from right to receive (in ounces) | oz     1      
Initial value of proceeds from right to receive equity     $ 1,091,000      
Net smelter royalty, percentage     1.00%      
Diablillos and M-18 properties            
Disposal Groups, Including Discontinued Operations 1 [Line Items]            
Sale of assets, value of equity received as consideration   $ 2,887,000        
Proceeds from sale of assets   $ 1,100,000     $ 250,000  
Net smelter royalty, percentage   1.00%        
Sale of assets, ownership percentage acquired as consideration   19.90%        
Sale of assets, financing value   $ 5,000,000        
Sale of assets, financing completed value   3,992,000        
Sale of assets, expected future proceeds from sale of assets   $ 13,000,000        
Sale of assets, expected future period of proceeds from sale of assets   4 years        
Sale of assets, expected future proceeds from sale of assets, initial value   $ 7,452,000        
Discount rate used in current measurement of expected future proceeds from sale of assets   20.00%        
Berenguela project            
Disposal Groups, Including Discontinued Operations 1 [Line Items]            
Sale of assets, shares received as consideration | shares 145,881,177          
Sale of assets, value of equity received as consideration $ 1,098,000          
Initial value of proceeds from right to receive equity $ 520,000          
Proceeds from sale of assets       $ 150,000    
Net smelter royalty, percentage 1.00%          
Sale of assets, expected future proceeds from sale of assets $ 12,000,000          
Sale of assets, expected future period of proceeds from sale of assets 5 years          
Sale of assets, expected future proceeds from sale of assets, initial value $ 6,726,000          
Discount rate used in current measurement of expected future proceeds from sale of assets 15.00%