Accounting for Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2018

Accounting for Asset Retirement Obligations

Schedule of Change in Accounting Estimate

The assumptions used to calculate the increases to the Palo Verde ARO liability are as follows:

	Escalation Rate		Credit-Risk Adjusted Discount Rate
Original ARO liability	3.60	%	9.50	%
Incremental ARO liability (2010)	3.60	%	6.20	%
Incremental ARO liability (2016)	3.25	%	4.34	%

Schedule of Asset Retirement Obligations

	2018			2017			2016
ARO liability at beginning of year	$	93,029		$	81,800		$	81,621
Liabilities incurred	—			138			—
Liabilities settled	(272		)	(19		)	(6,993		)
Revisions to estimate	—			3,461			—
Accretion expense	8,351			7,649			7,172
ARO liability at end of year	$	101,108		$	93,029		$	81,800