Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2019

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations Table

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

	Year Ended December 31,
thousands	2019			2018
Carrying amount of asset retirement obligations at beginning of year	$	325,962		$	154,571
Liabilities incurred	27,360			34,558
Liabilities settled	(17,104		)	(12,432		)
Accretion expense	13,599			7,909
Revisions in estimated liabilities	9,051			141,356
Carrying amount of asset retirement obligations at end of year	$	358,868		$	325,962