Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2014

Asset Retirement Obligation Disclosure [Abstract]

Schedule of change in asset retirement obligation

During 2014 and 2013, our overall asset retirement obligation changed as follows (in thousands):

	2014			2013
Beginning balance	$	273,987		$	296,870
Accretion	17,962			31,461
New obligations	1,346			2,225
Changes in estimates of existing obligations (1)	23,031			(27,628		)
Property dispositions/obligations settled	(19,851		)	(28,941		)
Ending balance	$	296,475		$	273,987

(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 cost, discount rates, and the estimated remaining life of assets. The 2014 changes in estimates of existing obligations reflect an increase of $23 million due to revisions in the estimated remaining life of assets, inflation rates, discount rates, and current estimates for removal costs. The 2013 changes in estimates of existing obligations reflect a decrease of $28 million, primarily due to a decrease of $36 million due to revisions in the estimated remaining life of assets, inflation rates, discount rates, and current estimates for removal costs, partially offset by an increase of $9 million related to changes in timing and method of abandonment of our Eminence natural gas storage caverns that were associated with a leak in 2010.