Regulatory Assets and Liabilities (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Regulatory Assets [Line Items]
RegulatoryAssetsCurrent	$ 2,549	$ 2,278
Regulatory Assets, Noncurrent	60,298	59,605
Total regulatory assets	62,847	61,883
Regulatory Liabilities [Line Items]
Total regulatory liabilities	17,395	20,948
Fuel recovery
Regulatory Liabilities [Line Items]
RegulatoryLiabilityCurrent	0	3,562
Postretirement benefits
Regulatory Liabilities [Line Items]
RegulatoryLiabilityNoncurrent	17,395	17,386
Environmental costs
Regulatory Assets [Line Items]
RegulatoryAssetsCurrent	1,300	2,200
Regulatory Assets, Noncurrent	739	1,117
Fuel recovery
Regulatory Assets [Line Items]
RegulatoryAssetsCurrent	1,249	78
Grossed-up deferred taxes on equity funds used during construction [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	16,083	17,034
Levelized depreciation
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	33,979	33,485
Asset retirement obligations, net
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 9,497	$ 7,969