Derivative and Hedging Instruments (Details-1) (USD $)	Mar. 31, 2012 MW MWh Dth	Dec. 31, 2011 MWh Dth MW
Gross notional volume of open derivatives [Abstract]
Commodity derivative contracts - MWh	451,750	482,545
Commodity derivative contracts - Dth	2,970,000	4,030,000
Financial transmission rights - MW	962	2,382
Derivative collateral [Abstract]
Derivative collateral	$ 2,000,000	$ 3,000,000
Derivative fair values [Abstract]
Exchange traded and financial transmission rights	(2,500,000)	(2,800,000)
Purchased power agreement	(69,000,000)	(39,500,000)
Derivative instruments at fair value on the balance sheet [Line Items]
Derivative liability (current)	8,198,000	4,568,000
Derivative liability (long-term)	60,880,000	34,908,000
Commodity Derivative Contracts [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Other current assets	266,000	177,000
Other defered charges	153,000	92,000
Derivative liability (current)	2,723,000	3,060,000
Derivative liability (long-term)	160,000	231,000
Financial Transmission Rights [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Other current assets	0	186,000
Derivative liability (current)	40,000	0
Purchased Power Agreement [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Derivative liability (current)	8,130,000	4,600,000
Derivative liability (long-term)	$ 60,880,000	$ 34,920,000