Income Taxes Deferred Income Tax Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Components of Deferred Tax Assets [Abstract]
Deferred Tax Assets, Employee Benefits	$ 5,094	$ 5,008
Deferred Tax Assets, Operating Loss Carryforwards	10,441	28,072
Deferred Tax Assets,Regulatory Liabilities	13,433	14,644
Deferred Tax Assets, Other	2,381	3,049
Deferred Tax Assets, Valuation Allowance	0	0
Total Deferred Tax Assets, Net of Valuation Allowance	31,349	50,773
Components of Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Accelerated Depreciation and Other Plant Related Differenes	(154,989)	(148,254)
Deferred Tax Liabilities, Allowance for Funds Used Dring Construction	(5,499)	(5,559)
Deferred Tax Liabilities, Regulatory Assets	(5,767)	(5,019)
Deferred Tax Liability, Employee Benefits	(3,610)	(2,356)
Deferred Tax Liabilities Other	(3,771)	(3,753)
Total Deferred Tax Liabilities, Gross	(173,636)	(164,941)
Deferred Tax Liabilities, Net	$ (142,287)	$ (114,168)