Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2015

Asset Retirement Obligation Disclosure [Abstract]

Schedule of Change in Asset Retirement Obligation

The following tables present the details of ARO which are included on the accompanying Consolidated Balance Sheets in Other deferred credits and other liabilities (in thousands):

	December 31, 2014		Liabilities Incurred		Liabilities Settled			Accretion		Revisions to Prior Estimates  (a)			December 31, 2015
Electric Utilities	$	7,012	$	—	$	(2,733	)	$	183	$	—		$	4,462
Gas Utilities	291		—		(168		)	13		—			136
Coal Mining	19,138		—		—			993		(1,498		)	18,633
Oil and Gas	20,945		828		(1,792		)	1,371		152			21,504
Total	$	47,386	$	828	$	(4,693	)	$	2,560	$	(1,346	)	$	44,735

	December 31, 2013		Liabilities Incurred		Liabilities Settled			Accretion		Revisions to Prior Estimates (a)(b)			December 31, 2014
Electric Utilities	$	6,922	$	—	$	(85	)	$	175	$	—		$	7,012
Gas Utilities	274		—		—			17		—			291
Coal Mining	20,627		345		—			951		(2,785		)	19,138
Oil and Gas	24,028		68		(932		)	1,043		(3,262		)	20,945
Total	$	51,851	$	413	$	(1,017	)	$	2,186	$	(6,047	)	$	47,386

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(a) The Coal Mining Revision to Prior Estimates reflects the change in backfill yards and disturbed acreage used in calculating the estimated liability as well as changes in inflation rate assumptions.

(b) The Oil and Gas Revision to Prior Estimates was due to a change in useful well lives used in calculating the estimated liability.