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ASSET RETIREMENT OBLIGATIONS (Asset Retirement Obligations Operating Costs) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
ASSET RETIREMENT OBLIGATIONS [Abstract]      
Accretion $ 11,474 $ 11,601 $ 10,685
Depreciation 6,515 4,462 3,527
Total $ 17,989 $ 16,063 $ 14,212