Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2018

Asset Retirement Obligation Disclosure [Abstract]

Schedule of change in asset retirement obligation

During 2018 and 2017, our overall asset retirement obligation changed as follows (in thousands):

	2018			2017
Beginning balance	$	67,100		$	60,762
Accretion	4,359			3,968
New obligations	—			149
Changes in estimates of existing obligations (1)	(2,095		)	2,510
Property dispositions/obligations settled	(14		)	(289		)
Ending balance	$	69,350		$	67,100

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