Asset Retirement Obligations (Tables)

9 Months Ended

Sep. 30, 2021

Asset Retirement Obligation Disclosure [Abstract]

Change in asset retirement obligations

The following schedule shows the change in our asset retirement obligations for the nine months ended September 30, 2021 (dollars in thousands): 

	2021
Asset retirement obligations at January 1, 2021	$	705,083
Changes attributable to:
Accretion expense	28,541
Settlements	(3,225)
Estimated cash flow revisions	27,678
Asset retirement obligations at September 30, 2021	$	758,077