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ASSET RETIREMENT OBLIGATIONS (Asset Retirement Obligations Operating Costs) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
ASSET RETIREMENT OBLIGATIONS [Abstract]        
Accretion $ 3,259 $ 3,247 $ 6,455 $ 6,155
Depreciation 2,664 2,063 5,325 3,899
Total $ 5,923 $ 5,310 $ 11,780 $ 10,054