Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2020

Asset Retirement Obligation Disclosure [Abstract]

Change in asset retirement obligations

The following table shows the change in our asset retirement obligations for 2020 and 2019 (dollars in thousands):

	2020		2019
Asset retirement obligations at the beginning of year	$	657,218	$	726,545
Changes attributable to:
Accretion expense	38,652		39,726
Settlements	(9,710)		(12,591)
Estimated cash flow revisions	18,923		(96,462)
Asset retirement obligations at the end of year	$	705,083	$	657,218