Derivative and Hedging Instruments (Details-1) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015 Dth MWh	Dec. 31, 2014 Dth MWh	Mar. 31, 2014	Dec. 31, 2013
Gross Notional Volume of Open Derivatives
Derivative, right to reclaim collateral (receivable)	$ 600,000
Other Current Assets [Member]
Derivative fair values [Abstract]
Derivative fair value, net	268,000	1,001,000	351,000	411,000
Commodity Contracts And Financial Transimission Rights [Member]
Derivative fair values [Abstract]
Derivative fair value, net	(600,000)	(1,600,000)
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh)	408,920	448,000
Notional amount, decatherm measure (in Dth)	2,785,000	4,405,000
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	343,000	223,000
Liability Derivatives, fair value, gross basis	937,000	2,433,000
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	336,000	130,000
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	7,000	93,000
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis	821,000	2,262,000
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis	116,000	171,000
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)	691	1,854
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	38,000	642,000
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	38,000	642,000
Financial Transmission Rights [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis	0	0
Ten-year PPA [Member]
Derivative fair values [Abstract]
Derivative fair value, net	(53,400,000)	(53,400,000)
Liability Derivatives, fair value, gross basis	53,410,000	53,430,000
Ten-year PPA [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis	7,090,000	6,870,000
Ten-year PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis	$ 46,320,000	$ 46,560,000