Asset Retirement Obligations (Tables)

6 Months Ended

Jun. 30, 2020

Asset Retirement Obligation Disclosure [Abstract]

Change in asset retirement obligations

The following schedule shows the change in our asset retirement obligations for the six months ended June 30, 2020 (dollars in thousands): 

	2020
Asset retirement obligations at January 1, 2020	$	657,218
Changes attributable to:
Accretion expense	20,410
Settlements	(4,324		)
Estimated cash flow revisions	(5,352		)
Asset retirement obligations at June 30, 2020	$	667,952