Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2021

Asset Retirement Obligation Disclosure [Abstract]

Change in asset retirement obligations

The following table shows the change in our AROs (dollars in thousands):

	2021		2020
Asset retirement obligations at the beginning of year	$	705,083	$	657,218
Changes attributable to:
Accretion expense	38,437		38,652
Settlements	(4,111)		(9,710)
Estimated cash flow revisions	27,973		18,923
Asset retirement obligations at the end of year	$	767,382	$	705,083