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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - (Details)
 12 Months Ended
Dec. 31, 2018
multiple
$ / oz
$ / bbl
Dec. 31, 2017
multiple
$ / oz
$ / bbl
Gold    
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES    
Estimated price for next twelve months 1,300 1,300
Estimated price second fiscal year 1,300 1,300
Estimated long-term price 1,300 1,300
Silver    
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES    
Estimated price for next twelve months 18.00 19.00
Estimated price second fiscal year 18.00 19.00
Estimated long-term price 18.00 19.00
WTI oil    
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES    
Estimated short-term and long-term price | $ / bbl 65 55
Minimum    
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES    
Useful life of mobile and other equipment 2 years  
Projected cash flow period P7Y  
Real discount rate 4.86% 4.35%
Net asset value multiple | multiple 0.9 0.8
Maximum    
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES    
Maximum measurement period for business combinations 1 year  
Useful life of mobile and other equipment 10 years  
Projected cash flow period P25Y  
Real discount rate 7.12% 7.10%
Net asset value multiple | multiple 1.4 1.6