Segment Information Depreciation and Amortization, by Segment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 25,592	$ 24,757
Electricity Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	12,767	11,630
Gas Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	6,649	6,841
Water Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	6,094	6,269
Corporate Unallocated [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 82	$ 17