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ORGANIZATION AND ACCOUNTING POLICIES - Asset Retirement Obligations & Capitalized Interest (Details 6) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Asset Retirement Obligations    
Fair market value of cash held in escrow that is legally restricted for potential plugging and abandonment liability $ 2,900  
Reconciliation of asset retirement obligations    
Balance at beginning of year 29,771 $ 26,785
Liabilities incurred in current year 9 1,768
Obligations on properties acquired   320
Liabilities settled in current year (1,232) (1,623)
Accretion expense 2,857 2,521
Carrying amount 31,405 29,771
Interest costs capitalized $ 9,000 $ 5,000