Summary of Significant Accounting Policies (Utility Plant) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			34 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Aug. 21, 2013	Oct. 27, 2010
Public Utility, Property, Plant and Equipment [Line Items]
Immediate increase requested, percentage					38.00%
Total increase requested, percentage					71.00%
Regulatory Rate Filings, Increase, Percent of Authorized Revenue Approved				33.00%
Capitalized interest costs	$ 905	$ 913	$ 699
Construction in progress	30,846	24,298
Major components of depreciable plant and equipment [Abstract]
Equipment	226,557	214,670
Transmission and distribution	967,031	892,957
Office buildings and other structures	60,998	58,593
Total depreciable plant and equipment	1,254,586	1,166,220
Estimated Useful Lives of Plant and Equipment [Abstract]
Depreciation expense as percentage of beginning of year balance of depreciable plant	3.40%	3.50%	3.50%
Customer Refund for Over Rate Collections				982
Minimum [Member]
Estimated Useful Lives of Plant and Equipment [Abstract]
Estimated service lives of assets	5 years
Estimated useful life of equipment	5 years
Estimated useful life of transmission and distribution plant	35 years
Estimated useful lives of office buildings and other structures	7 years
Useful life of intangible assets	5 years
Maximum [Member]
Estimated Useful Lives of Plant and Equipment [Abstract]
Estimated service lives of assets	75 years
Estimated useful life of equipment	35 years
Estimated useful life of transmission and distribution plant	75 years
Estimated useful lives of office buildings and other structures	50 years
Useful life of intangible assets	70 years
General and Administrative Expense [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation	1,556	1,531	1,516
Water Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation	$ 32,616	$ 31,005	$ 29,141