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ASSET RETIREMENT OBLIGATIONS - Changes in Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Asset retirement obligations as of the beginning of the year, including current portion $ 225,866 $ 316,409 $ 502,513
Liabilities incurred 2,338 15,933 28,606
Liabilities settled (19,630) (72,713) (55,839)
Divestment of properties 0 (248) (137,801)
Accretion expense 40,229 25,988 28,411
Revision of estimates (6,784) (59,503) (49,481)
Asset retirement obligations as of the end of the year, including current portion $ 242,019 $ 225,866 $ 316,409