XML 156 R111.htm IDEA: XBRL DOCUMENT v3.8.0.1
ASSET RETIREMENT OBLIGATIONS (Asset Retirement Obligations Operating Costs) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
ASSET RETIREMENT OBLIGATIONS [Abstract]      
Accretion $ 11,415 $ 11,059 $ 11,474
Depreciation 6,302 6,353 6,515
Total $ 17,717 $ 17,412 $ 17,989