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GOODWILL IMPAIRMENT (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2020
Mar. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
GOODWILL IMPAIRMENT        
Goodwill $ 4,400 $ 4,373 $ 4,373 $ 136,400
Impairments of goodwill 132,026      
Hamilton mining complex        
GOODWILL IMPAIRMENT        
Goodwill       $ 132,000
Impairments of goodwill $ 132,000