Regulatory Assets and Liabilities, Regulatory Liabilities (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	$ 9,717	$ 6,086
Regulatory Liability, Noncurrent	126,424	123,746
Plant Removal Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	0	0
Regulatory Liability, Noncurrent	116,293	113,949
Regulatory liability, remaining amortization period	Plant lives
DOE Settlement
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	6,814	5,628
Regulatory Liability, Noncurrent	0	0
Regulatory liability, remaining amortization period	Less than one year
Investment Tax Credit Deferrals
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	0	0
Regulatory Liability, Noncurrent	9,976	9,626
Regulatory liability, remaining amortization period	Various
Conservation Programs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	1,187	73
Regulatory Liability, Noncurrent	0	0
Regulatory liability, remaining amortization period	Less than one year
Deferred Electric Production And Natural Gas Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	1,542	134
Regulatory Liability, Noncurrent	0	0
Regulatory liability, remaining amortization period	Less than one year
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	174	251
Regulatory Liability, Noncurrent	$ 155	$ 171
Regulatory liability, remaining amortization period	Various