Asset Retirement Obligation

12 Months Ended

Dec. 31, 2014

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations

Activity related to the Company's asset retirement obligations is as follows:



(In thousands)	Year Ended December 31, 2014
Balance at beginning of period	$	75,853
Liabilities incurred	7,220
Liabilities settled and divested	(1,474		)
Liabilities acquired	1,206
Accretion expense	5,110
Change in estimate	38,740
Balance at end of period	$	126,655

The change in estimate during 2014 is attributable to an increase in cost of materials and services. The increase is primarily due to an increase in demand, more costly and rigorous plugging and abandonment techniques associated with the Company's wells in certain areas of its operations and the lack of availability of service providers in areas with minimal activity.

As of both December 31, 2014 and 2013, approximately $2.0 million is included in accrued liabilities in the Consolidated Balance Sheet, which represents the current portion of the Company’s asset retirement obligation.