Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2020

Asset Retirement Obligation Disclosure [Abstract]

Schedule of change in asset retirement obligation

During 2020 and 2019, our overall asset retirement obligation changed as follows (in thousands): 

	2020		2019
Beginning balance	$	459,209	$	394,323
Accretion	23,142		21,806
New obligations	1,154		103
Changes in estimates of existing obligations (1)	(21,889)		49,070
Property dispositions/obligations settled	(11,115)		(6,093)
Ending balance	$	450,501	$	459,209

(1)    Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rate, current estimates for removal costs, discount rates, and the estimated remaining life of assets. The decrease in 2020 is primarily due to a decrease in the inflation rate. The increase in 2019 is primarily due to an increase in the inflation rate and a decrease in the discount rate.