Derivative and Hedging Instruments (Details-1) $ in Thousands		12 Months Ended
		Dec. 31, 2016 USD ($) Dth MWh MW	Dec. 31, 2015 USD ($) Dth MWh MW	Dec. 31, 2014 USD ($)
Derivative Fair Values [Abstract]
Derivative, right to reclaim collateral (receivable)		$ 0	$ 1,000
Other Current Assets [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net		230	1,208	$ 1,001
Commodity Contracts and Financial Transimission Rights [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net		$ 1,300	$ (800)
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh		393,395	355,580
Notional amount, decatherm measure (in Dth) | Dth		4,195,000	5,037,500
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		$ 1,384	$ 290
Liability Derivatives, fair value, gross basis		218	1,336
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	1,227
Liability Derivatives, fair value, gross basis	[1]	164
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	157
Liability Derivatives, fair value, gross basis	[1]	$ 54
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]		146
Liability Derivatives, fair value, gross basis	[1]		1,266
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]		144
Liability Derivatives, fair value, gross basis	[1]		$ 70
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) | MW		2,251	2,000
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		$ 143	$ 234
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		143	234
Liability Derivatives, fair value, gross basis		$ 0	$ 0
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		3,250	3,850
Derivative Fair Values [Abstract]
Derivative fair value, net		$ (50,600)	$ (53,300)
Liability Derivatives, fair value, gross basis		50,590	53,270
PPA [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Liability Derivatives, fair value, gross basis		7,620	8,340
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Liability Derivatives, fair value, gross basis		$ 42,970	$ 44,930

[1] As of December 31 , 2015 , collateral of $ 1.0 million was posted against and netted with derivative liability positions on the consolidated balance sheets. No collateral was posted against derivative positions as of December 31, 2016 .