Commitments and Contingencies, Asset Retirement Obligations (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 19,375,000	[1]	$ 17,607,000
Liabilities recognized	136,000		0
Liabilities settled	0		(118,000)
Accretion	1,100,000		1,008,000
Cash flow revisions	5,420,000		878,000
Ending balance	26,031,000	[2]	19,375,000	[1]
Electric Plant Steam Production Asbestos
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	11,608,000	[1]	10,979,000
Liabilities recognized	0		0
Liabilities settled	0		(118,000)
Accretion	795,000		747,000
Cash flow revisions	4,554,000		0
Ending balance	16,957,000	[2]	11,608,000	[1]
Electric Plant Steam Production Ash Containment
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	809,000	[1]	764,000
Liabilities recognized	0		0
Liabilities settled	0		0
Accretion	51,000		48,000
Cash flow revisions	749,000		(3,000)
Ending balance	1,609,000	[2]	809,000	[1]
Electric Plant Electric Distribution
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	6,104,000	[1]	5,303,000
Liabilities recognized	0		0
Liabilities settled	0		0
Accretion	223,000		171,000
Cash flow revisions	0		630,000
Ending balance	6,327,000	[2]	6,104,000	[1]
Electric Plant Other
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	854,000	[1]	561,000
Liabilities recognized	136,000		0
Liabilities settled	0		0
Accretion	31,000		42,000
Cash flow revisions	117,000		251,000
Ending balance	$ 1,138,000	[2]	$ 854,000	[1]

[1] There were no new ARO liabilities recognized during the year ended Dec. 31, 2013.

[2] There were no ARO liabilities settled during the year ended Dec. 31, 2014.