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ASSET RETIREMENT OBLIGATIONS (Asset Retirement Obligations Operating Costs) (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
ASSET RETIREMENT OBLIGATIONS [Abstract]        
Accretion $ 2,857 $ 2,692 $ 8,620 $ 8,163
Depreciation 1,494 1,469 4,741 4,783
Total $ 4,351 $ 4,161 $ 13,361 $ 12,946