Derivative and Hedging Instruments (Details-1) (USD $)	Mar. 31, 2013 MW MWh Dth	Dec. 31, 2012 MWh Dth MW
Gross notional volume of open derivatives [Abstract]
Commodity derivative contracts - MWh	331,315	444,650
Commodity derivative contracts - Dth	1,360,000	1,980,000
Financial transmission rights - MW	1,085	2,670
Derivative fair values [Abstract]
Exchange traded and financial transmission rights	$ 1,500,000	$ 300,000
Purchased power agreement	(70,700,000)	(72,600,000)
Derivative instruments at fair value on the balance sheet [Line Items]
Derivative liability (current)	8,880,000	9,270,000
Derivative liability (long-term)	61,810,000	63,320,000
Commodity Derivative Contracts [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Other current assets	1,343,000	365,000
Other defered charges	158,000	95,000
Derivative liability (current)	30,000	394,000
Derivative liability (long-term)	0	11,000
Offsetting Assets [Line Items]
Gross amounts	1,502,000	460,000
Gross amounts offset in balance sheet	(30,000)	(405,000)
Collateral posted against derivative positions	(465,000)	0
Net amount presented in balance sheet	1,007,000	55,000
Financial Transmission Rights [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Other current assets	22,000	206,000
Derivative liability (current)	0	0
Offsetting Assets [Line Items]
Gross amounts	22,000	206,000
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	22,000	206,000
Purchased Power Agreement [Member]
Derivative instruments at fair value on the balance sheet [Line Items]
Derivative liability (current)	8,880,000	9,270,000
Derivative liability (long-term)	$ 61,810,000	$ 63,320,000