Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2015

Asset Retirement Obligation Disclosure [Abstract]

Schedule of change in asset retirement obligation

During 2015 and 2014, our overall asset retirement obligation changed as follows (in thousands):

	2015			2014
Beginning balance	$	94,678		$	60,753
Accretion	6,870			5,602
New obligations	2,721			157
Changes in estimates of existing obligations (1)	(21,815		)	28,171
Property Dispositions & Settlements	—			(5		)
Ending balance	$	82,454		$	94,678

(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 decrease in 2015 is primarily attributed to decreases in current estimates for removal costs and inflation rate and an increase in the discount rate. The increase in 2014 is primarily attributed to increases in current estimates for removal costs and inflation rate and a decrease in the discount rate.