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Derivative and Hedging Instruments (Details-4) (USD $) |  |  | 3 Months Ended
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Mar. 31, 2013 | Dec. 31, 2012 | Mar. 31, 2013 Commodity Derivative Contracts [Member] Regulated Gas Revenues [Member] | Mar. 31, 2012 Commodity Derivative Contracts [Member] Regulated Gas Revenues [Member] | Mar. 31, 2013 Commodity Derivative Contracts [Member] Fuel For Electric Generation Purchased Power [Member] | Mar. 31, 2012 Commodity Derivative Contracts [Member] Fuel For Electric Generation Purchased Power [Member] | Mar. 31, 2013 Commodity Derivative Contracts [Member] Cost Of Gas Sold Expense [Member] | Mar. 31, 2012 Commodity Derivative Contracts [Member] Cost Of Gas Sold Expense [Member] | Mar. 31, 2013 Financial Transmission Rights [Member] Regulated Gas Revenues [Member] | Mar. 31, 2012 Financial Transmission Rights [Member] Regulated Gas Revenues [Member] | Mar. 31, 2013 Financial Transmission Rights [Member] Fuel For Electric Generation Purchased Power [Member] | Mar. 31, 2012 Financial Transmission Rights [Member] Fuel For Electric Generation Purchased Power [Member] | Mar. 31, 2013 Financial Transmission Rights [Member] Cost Of Gas Sold Expense [Member] | Mar. 31, 2012 Financial Transmission Rights [Member] Cost Of Gas Sold Expense [Member] | Mar. 31, 2013 Purchased Power Agreement [Member] Regulated Gas Revenues [Member] | Mar. 31, 2012 Purchased Power Agreement [Member] Regulated Gas Revenues [Member] | Mar. 31, 2013 Purchased Power Agreement [Member] Fuel For Electric Generation Purchased Power [Member] | Mar. 31, 2012 Purchased Power Agreement [Member] Fuel For Electric Generation Purchased Power [Member] | Mar. 31, 2013 Purchased Power Agreement [Member] Cost Of Gas Sold Expense [Member] | Mar. 31, 2012 Purchased Power Agreement [Member] Cost Of Gas Sold Expense [Member]
Realized losses (gains) on income statement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Realized losses (gains) on income statement |  |  | $ 0 | $ 0 | $ 22,000 | $ 1,928,000 | $ 608,000 | $ 3,090,000 | $ 0 | $ 0 | $ (158,000) | $ 66,000 | $ 0 | $ 0 | $ 0 | $ 0 | $ 1,278,000 | $ 0 | $ 0 | $ 0
Derivative collateral required to be posted for ten-year PPA [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum collateral required | 20,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum collateral required | 40,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required collateral posted | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Counterparties in net liability position [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Counterparties in net liability position | $ 0 | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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- Definition Maximum collateral required to be posted for ten-year PPA. + References No definition available. + Details
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- Definition Minimum collateral required to be posted for ten-year PPA. + References No definition available. + Details
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- Definition Counterparties in a net liability position. + References No definition available. + Details
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- Details
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- Definition The amount of the right to reclaim cash collateral under the ten-year PPA master netting arrangements that have not been offset against net derivative instrument positions. + References No definition available. + Details
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- Details
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- Definition The amount of net gains and losses recognized in income during the period on derivative instruments designated and qualifying as hedging instruments in fair value hedges and related hedged items designated and qualifying in fair value hedges, on derivative instruments designated and qualifying as hedging instruments in cash flow hedges, and on derivative instruments not designated as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 205G -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5618551-113959 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624171-113959 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44C -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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