Derivative and Hedging Instruments (Details-1) (USD $)	12 Months Ended
	Dec. 31, 2014 Dth MWh	Dec. 31, 2013 MWh Dth	Dec. 31, 2012
Gross Notional Volume of Open Derivatives
Derivative, right to reclaim collateral (receivable)	$ 2,200,000
Other Current Assets [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net	1,001,000	411,000	574,000
Commodity Contracts and Financial Transimission Rights [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net	(1,600,000)	1,800,000
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh)	448,000	458,660
Notional amount, decatherm measure (in Dth)	4,405,000	3,750,000
Derivative Fair Values [Abstract]
Derivative fair value, gross asset	223,000	1,523,000
Derivative fair value, gross liability	2,433,000	99,000
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Derivative fair value, gross asset	130,000	1,356,000
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member]
Derivative Fair Values [Abstract]
Derivative fair value, gross asset	93,000	167,000
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Derivative fair value, gross liability	2,262,000	51,000
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Derivative fair value, gross liability	171,000	48,000
Energy Related Commodity Contract [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Maximum term of derivative hedging contract	4 years
Financial Transmission Rights [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW)	1,854	1,984
Derivative Fair Values [Abstract]
Derivative fair value, gross asset	642,000	363,000
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Derivative fair value, gross asset	642,000	363,000
Financial Transmission Rights [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Derivative fair value, gross liability	0	0
Ten-year PPA [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net	(53,400,000)	(65,700,000)
Derivative fair value, gross liability	53,430,000	65,680,000
Ten-year PPA [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Derivative fair value, gross liability	6,870,000	7,750,000
Ten-year PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Derivative fair value, gross liability	$ 46,560,000	$ 57,930,000