Asset Retirement Obligations

12 Months Ended

Dec. 31, 2015

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations

11.  ASSET RETIREMENT OBLIGATIONS

The following table provides a summary of changes in asset retirement obligations:

	Year Ended December 31,
thousands	2015			2014
Carrying amount of asset retirement obligations at beginning of year	$	110,735		$	78,535
Liabilities incurred	9,121			13,982
Liabilities settled	(7,377		)	(4,195		)
Accretion expense	5,943			4,879
Revisions in estimated liabilities	2,105			17,534
Carrying amount of asset retirement obligations at end of year	$	120,527		$	110,735

The liabilities incurred for the year ended December 31, 2015, represented additions in asset retirement obligations primarily due to capital expansions at the DJ Basin, Granger and Brasada complexes and the Hilight and Non-Operated Marcellus Interest systems. Revisions in estimated liabilities for the year ended December 31, 2015, are related to (i) changes in expected timing of settlement primarily at the DBM and DJ Basin complexes and Hugoton and DBJV systems, and (ii) changes in property lives primarily at the Granger, Brasada and Red Desert complexes and the Hilight and Non-Operated Marcellus Interest systems.

The liabilities incurred for the year ended December 31, 2014, increased primarily due to the acquisition of DBM in the fourth quarter of 2014 and continued capital expansion at the DJ Basin complex. Revisions in estimated liabilities for the year ended December 31, 2014, are related to changes in property lives and changes in the expected timing of settlement, primarily at the DJ Basin complex, Granger complex, Hugoton and Hilight systems, MIGC, OTTCO, Brasada complex and Non-Operated Marcellus Interest systems.