Annual report pursuant to Section 13 and 15(d)

Note 6 - Asset Retirement Obligations - Changes to Asset Retirement Obligation (Details)

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Note 6 - Asset Retirement Obligations - Changes to Asset Retirement Obligation (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Asset retirement obligations, beginning of period $ 355,594 $ 310,137  
Liabilities settled (3,339) (11,443)  
Asset retirement obligations accretion 22,521 19,460 $ 18,431
Liabilities incurred and assumed through acquisition 4,860 29,887  
Revisions of estimated liabilities (1) [1] 13,068 7,553  
Asset retirement obligations, end of period 392,704 355,594 $ 310,137
Less current portion 17,188 21,991  
Long-term $ 375,516 $ 333,603  
[1] Revisions in 2020 and 2019 were due to changes in scope, weather impact, revisions to actual expenses versus estimates and revisions related to non-operated properties.