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Asset Retirement Obligations - Asset Retirement Obligations (Detail) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2020
Dec. 31, 2019
Asset Retirement Obligation [Abstract]    
Beginning of period $ 251,076 $ 312,754
Liabilities incurred 1,618 4,063
Acquisitions 123 0
Liabilities settled (1,416) (5,953)
Disposition of wells [1] (126,268) (82,576)
Accretion expense 4,729 15,658
Change in estimate 2,507 7,130
End of period 132,369 251,076
Less current portion (2,393) (2,393)
Long-term asset retirement obligations $ 129,976 $ 248,683
[1] The six months ended June 30, 2020 primarily represents the completion of the sale of our shallow legacy assets in Northwest Pennsylvania.