The amount of deferred gains (losses) relating to closed natural gas positions.

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The amount of mark-to-market gain (loss) on the derivative or group of derivatives included in earnings in the period.

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The period of time (in years) covered by the hedged contractors for natural gas fuel costs.

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The amount of unrealized gains (losses) from the net mark-to-market impact relating to open natural gas positions.

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- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12

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- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 45
-Subparagraph b(2)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6887037&loc=d3e80748-113994

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- Definition

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
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-Subparagraph b
-Clause 4
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-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
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-Publisher FASB
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The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (b)
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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-Paragraph 44C
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-Clause 2
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The amount of loss 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.

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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.

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-Publisher FASB
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The percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need.

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Fair Value Accounting, Effect of Derivatives on Consolidated Statements of Income (Details) (USD $)			3 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended	3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010 Derivatives Designated as Hedging Instruments [Member] Interest Rate Swap [Member] OCI [Member]	Jun. 30, 2010 Derivatives Designated as Hedging Instruments [Member] Interest Rate Swap [Member] OCI [Member]	Jun. 30, 2011 Derivatives Designated as Hedging Instruments [Member] Treasury Rate Locks [Member] Interest Expense [Member]	Jun. 30, 2010 Derivatives Designated as Hedging Instruments [Member] Treasury Rate Locks [Member] Interest Expense [Member]	Jun. 30, 2011 Derivatives Designated as Hedging Instruments [Member] Treasury Rate Locks [Member] Interest Expense [Member]	Jun. 30, 2010 Derivatives Designated as Hedging Instruments [Member] Treasury Rate Locks [Member] Interest Expense [Member]	Jun. 30, 2012 Derivatives Designated as Hedging Instruments [Member] Treasury Rate Locks [Member] Interest Expense [Member]	Jun. 30, 2011 Derivatives Not Designated As Hedging Instruments [Member]	Jun. 30, 2010 Derivatives Not Designated As Hedging Instruments [Member]	Jun. 30, 2011 Derivatives Not Designated As Hedging Instruments [Member]	Jun. 30, 2010 Derivatives Not Designated As Hedging Instruments [Member]	Jun. 30, 2011 Derivatives Not Designated As Hedging Instruments [Member] Fuel Cost Hedges [Member]	Dec. 31, 2010 Derivatives Not Designated As Hedging Instruments [Member] Fuel Cost Hedges [Member]	Jun. 30, 2011 Derivatives Not Designated As Hedging Instruments [Member] Fuel Cost Hedges [Member] Fuel Used For Electric Generation [Member]	Jun. 30, 2010 Derivatives Not Designated As Hedging Instruments [Member] Fuel Cost Hedges [Member] Fuel Used For Electric Generation [Member]	Jun. 30, 2011 Derivatives Not Designated As Hedging Instruments [Member] Fuel Cost Hedges [Member] Fuel Used For Electric Generation [Member]	Jun. 30, 2010 Derivatives Not Designated As Hedging Instruments [Member] Fuel Cost Hedges [Member] Fuel Used For Electric Generation [Member]	Jun. 30, 2010 Derivatives Not Designated As Hedging Instruments [Member] Economic Hedges [Member] Other Operations Revenue [Member]	Jun. 30, 2010 Derivatives Not Designated As Hedging Instruments [Member] Economic Hedges [Member] Other Operations Revenue [Member]
Derivative, gain (loss) recognized in income [Abstract]
Amount of gain (loss) recognized in income on derivatives										$ 5,203,000	$ (14,290,000)	$ 8,997,000	$ (22,706,000)			$ 5,203,000	$ (14,402,000)	$ 8,997,000	$ (22,215,000)	$ 112,000	$ (491,000)
Mark-to-market gains (losses)																				400,000	0
Unrealized gains (losses)														(7,700,000)	(15,100,000)
Deferred gains (losses)														(2,100,000)	(1,600,000)
Amount of (loss) gain recognized in OCI			(60,000)	(341,000)
Amount of (loss) gain reclassified from accumulated OCI into income (effective portion)			(197,000)	(399,000)	89,000	42,000	177,000	83,000
Cash flow hedge gain (loss) expected to be reclassed from accumulated OCI over the next 12 months									$ 400,000
Natural gas requirements hedged [Abstract]
Millions MMBtus hedged for natural gas fuel costs	5.5	9.4
Estimated natural gas requirements covered (in hundredths)	7.00%	11.00%
Estimated natural gas requirements period (in years)	two-year	two-year