Asset Retirement Obligations (Tables)

9 Months Ended

Sep. 30, 2016

Asset Retirement Obligation Disclosure [Abstract]

Change in asset retirement obligations

The following schedule shows the change in our asset retirement obligations for the nine months ended September 30, 2016 (dollars in thousands): 

Asset retirement obligations at January 1, 2016	$	443,576
Changes attributable to:
Accretion expense	19,868
Settlements	(11,891		)
Newly incurred or acquired liabilities	18,927
Asset retirement obligations at September 30, 2016	$	470,480