Derivative and Hedging Instruments (Details-1) (USD $)	Sep. 30, 2012 MW MWh Dth	Dec. 31, 2011 MWh Dth MW
Gross notional volume of open derivatives [Abstract]
Commodity derivative contracts - MWh	440,320	482,545
Commodity derivative contracts - Dth	4,170,000	4,030,000
Financial transmission rights - MW	4,069	2,382
Derivative collateral [Abstract]
Derivative collateral	$ 0	$ 3,000,000
Derivative fair values [Abstract]
Exchange traded and financial transmission rights	(1,800,000)	(2,800,000)
Purchased power agreement	(77,100,000)	(39,500,000)
Derivative instruments at fair value on the balance sheet [Line Items]
Derivative liability (current)	9,600,000	4,568,000
Derivative liability (long-term)	67,490,000	34,908,000
Commodity Derivative Contracts [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Other current assets	1,463,000	177,000
Other defered charges	114,000	92,000
Derivative liability (current)	245,000	3,060,000
Derivative liability (long-term)	60,000	231,000
Financial Transmission Rights [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Other current assets	561,000	186,000
Derivative liability (current)	0	0
Purchased Power Agreement [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Derivative liability (current)	9,600,000	4,600,000
Derivative liability (long-term)	$ 67,490,000	$ 34,920,000