Segment Information Depreciation and Amortization, by Segment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 24,627	$ 24,718	$ 75,233	$ 73,749
Electricity Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	11,596	11,740	36,754	35,084
Gas Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	6,486	6,736	19,590	20,211
Water Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	6,466	6,201	18,679	18,379
Corporate Unallocated [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 79	$ 41	$ 210	$ 75