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ASSET RETIREMENT OBLIGATIONS (Asset Retirement Obligations Operating Costs) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
ASSET RETIREMENT OBLIGATIONS [Abstract]      
Accretion $ 10,776 $ 11,415 $ 11,059
Depreciation 6,034 6,302 6,353
Total $ 16,810 $ 17,717 $ 17,412