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Utility Plant and Intangible Assets (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of the beginning and ending aggregate carrying amount of the asset retirement obligations
Obligation at the beginning of the period	$ 2,989	$ 2,910
Additional liabilities incurred	48	3
Liabilities settled	(209)	(122)
Accretion	190	198
Obligation at the end of the period	$ 3,018	$ 2,989

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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