Depreciation and Amortization, by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 16,082	$ 18,998	$ 51,563	$ 57,790
Electricity Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	6,682	8,878	21,715	27,427
Gas Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	5,595	4,743	15,484	15,316
Water Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	5,022	5,280	14,040	14,806
Corporate Unallocated [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ (1,217)	$ 97	$ 324	$ 241