Fair Value of Financial Instruments (Details-3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes in level 3 assets and liabilities measured at fair value on a recurring basis [Abstract]
Beginning balance,	$ (40,661)	$ (19,216)	$ (13,047)
Realized and unrealized gains (losses):
Included in regulatory liabilities (assets)	(31,685)	(21,445)	(6,169)
Included in other comprehensive income	0	0	0
Included in earnings	(5,005)	868	(1,482)
Included in current assets	0	0	0
Purchases	13,370	341	0
Sales	92	144	134
Issuances	0	0	0
Settlements	(8,457)	(1,353)	1,348
Transfers in or out of level 3	0	0	0
Ending balance,	(72,346)	(40,661)	(19,216)
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	0	0	0
Realized and unrealized gains (losses) included in income for level 3 instruments [Line Items]
Realized and unrealized gains (losses) included in income for level 3 instruments.	(5,005)	868	(1,482)
Purchased Power Expense [Member]
Realized and unrealized gains (losses) included in income for level 3 instruments [Line Items]
Realized and unrealized gains (losses) included in income for level 3 instruments.	(5,005)	868	(1,461)
Cost Of Gas Sold Expense [Member]
Realized and unrealized gains (losses) included in income for level 3 instruments [Line Items]
Realized and unrealized gains (losses) included in income for level 3 instruments.	$ 0	$ 0	$ (21)

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This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in current assets.

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This item represents the amount of the total realized and unrealized gains or losses for the period which are included in the statement of income (or changes in net assets); the fair value of which assets and liabilities was or is measured on a recurring basis using significant unobservable inputs (Level 3).

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This item represents the amount of the total change in unrealized (holding) gains or losses for the period which are included in the statement of income (or changes in net assets) in investment income. Such unrealized (holding) gains or losses relate to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

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Issues that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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Purchases that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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Sales that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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Settlements that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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This element represents [net] transfers in to and out of assets measured at fair value on a recurring basis using unobservable inputs (Level 3) which have taken place during the period.

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This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

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