Derivative and Hedging Instruments (Details-1) (USD $)	Sep. 30, 2011 MW Tons Dth MWh	Dec. 31, 2010 Dth MW MWh
Gross Notional Volume of Open Derivatives [Abstract]
Commodity derivative contracts - MWh	415,845	544,820
Commodity derivative contracts - Dth	6,850,000	5,420,000
Financial transmission rights - MW	3,724	2,609
Derivative Collateral [Abstract]
Derivative collateral	$ 400,000	$ 500,000
Derivative Fair Values [Abstract]
Exchange traded and financial transmission rights	(200,000)	(200,000)
Purchased power agreement	(26,400,000)	(19,000,000)
Commodity Derivative Contracts [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Other current assets	583,000	649,000
Other defered charges	15,000	214,000
Other current liabilities	1,003,000	1,227,000
Other deferred liabilities	8,000	167,000
Financial Transmission Rights [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Other current assets	180,000	312,000
Other current liabilities	0	0
Purchased Power Agreement [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Other current liabilities	2,260,000	0
Other deferred liabilities	$ 24,090,000	$ 19,010,000