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Decommissioning and Other Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2017
Dec. 31, 2016
Decommissioning and Other Asset Retirement Obligations Detail [Table]      
Beginning balance for the period, as reported $ 55,482 $ 55,478  
Activity in the period:      
Accretion of liability 551 1,031  
Retirement obligations incurred 0 0  
Revisions in estimated cash flows (2) (14)  
Settlement of retirement obligations (32) (496)  
Ending balance as of June 30 55,999 55,999  
Value of asset retirement obligations associated with non-operated properties $ 9,800 $ 9,800 $ 9,400