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ASSET RETIREMENT OBLIGATIONS (Asset Retirement Obligations Operating Costs) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
ASSET RETIREMENT OBLIGATIONS [Abstract]    
Accretion $ 2,684 $ 2,882
Depreciation 1,337 1,632
Total $ 4,021 $ 4,514