Commitments and Contingencies, Asset Retirement Obligations (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 26,031,000	[1]	$ 19,375,000
Liabilities Incurred	0		136,000
Liabilities settled	0		0
Accretion	1,383,000		1,100,000
Cash flow revisions	(181,000)		5,420,000	[2]
Ending balance	27,233,000	[3]	26,031,000	[1]
Electric Plant Steam Production Asbestos
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	16,957,000	[1]	11,608,000
Liabilities Incurred	0		0
Liabilities settled	0		0
Accretion	1,024,000		795,000
Cash flow revisions	0		4,554,000	[2]
Ending balance	17,981,000	[3]	16,957,000	[1]
Electric Plant Steam Production Ash Containment
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	1,609,000	[1]	809,000
Liabilities Incurred	0		0
Liabilities settled	0		0
Accretion	85,000		51,000
Cash flow revisions	(181,000)		749,000	[2]
Ending balance	1,513,000	[3]	1,609,000	[1]
Electric Plant Electric Distribution
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	6,327,000	[1]	6,104,000
Liabilities Incurred	0		0
Liabilities settled	0		0
Accretion	232,000		223,000
Cash flow revisions	0		0	[2]
Ending balance	6,559,000	[3]	6,327,000	[1]
Electric Plant Other
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	1,138,000	[1]	854,000
Liabilities Incurred	0		136,000
Liabilities settled	0		0
Accretion	42,000		31,000
Cash flow revisions	0		117,000	[2]
Ending balance	$ 1,180,000	[3]	$ 1,138,000	[1]

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

[2] In 2014, revisions were made to various AROs due to revised estimated cash flows and the timing of those cash flows.

[3] There were no ARO liabilities recognized or settled during the year ended Dec. 31, 2015.