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ASSET RETIREMENT OBLIGATIONS (Asset Retirement Obligations Operating Costs) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
ASSET RETIREMENT OBLIGATIONS [Abstract]        
Accretion $ 2,881 $ 2,716 $ 5,763 $ 5,472
Depreciation 1,615 1,621 3,247 3,314
Total $ 4,496 $ 4,337 $ 9,010 $ 8,786