Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2016

Asset Retirement Obligation Disclosure [Abstract]

Schedule of change in asset retirement obligation

During 2016 and 2015, our overall asset retirement obligation changed as follows (in thousands):

	2016			2015
Beginning balance	$	323,026		$	296,475
Accretion	35,740			25,178
New obligations	7,995			256
Changes in estimates of existing obligations (1)	(85,514		)	3,691
Property dispositions/obligations settled	(5,795		)	(2,574		)
Ending balance	$	275,452		$	323,026

(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 cost, discount rates, and the estimated remaining life of assets. The changes in estimates of existing obligations reflect a decrease of $86 million for 2016 and an increase of $4 million for 2015. The decrease in 2016 is due primarily to revisions in the estimated remaining life of assets and the current estimate to the inflation rate. The increase in 2015 is primarily due to current estimates for removal costs, inflation rate, and discount rates.