Commitments and Contingencies, Asset Retirement Obligations (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 17,607	$ 27,266
Liabilities settled	(118)	0
Accretion	1,008	1,675
Revisions to prior estimates	878	(11,334)
Ending balance	19,375	17,607
Electric Plant Steam Production Asbestos [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	10,979	20,803
Liabilities settled	(118)	0
Accretion	747	1,422
Revisions to prior estimates	0	(11,246)
Ending balance	11,608	10,979
Electric Plant Steam Production Ash Containment [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	764	719
Liabilities settled	0	0
Accretion	48	45
Revisions to prior estimates	(3)	0
Ending balance	809	764
Electric Plant Electric Distribution [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	5,303	5,202
Liabilities settled	0	0
Accretion	171	188
Revisions to prior estimates	630	(87)
Ending balance	6,104	5,303
Electric Plant Other [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	561	542
Liabilities settled	0	0
Accretion	42	20
Revisions to prior estimates	251	(1)
Ending balance	$ 854	$ 561