Depreciation and Amortization, by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 14,378	$ 16,674
Electricity Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	5,311	7,262
Gas Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	4,244	4,921
Water Operating Segment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	3,959	4,382
Corporate Unallocated [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 864	$ 109