Segment Information Depreciation and Amortization, by Segment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 25,014	$ 24,274	$ 50,606	$ 49,031
Electricity Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	12,391	11,714	25,158	23,344
Gas Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	6,455	6,634	13,104	13,475
Water Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	6,119	5,909	12,213	12,178
Corporate Unallocated [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 49	$ 17	$ 131	$ 34