Segment Information Information By Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 495,713	$ 506,859	$ 513,024	$ 497,590	$ 496,448	$ 469,528	$ 470,811	$ 446,746	$ 2,013,186	$ 1,883,533	$ 1,947,616
Gross Profit	$ 156,663	$ 170,749	$ 169,705	$ 163,203	$ 152,419	$ 147,290	$ 118,554	$ 138,422	660,320	556,685	614,050
Operating Income (Loss)									96,211	52,846	480
Total other income (expense)									(11,584)	(15,744)	(18,745)
Income (loss) before income taxes									84,627	37,102	(18,265)
Depreciation and amortization									68,318	75,993	98,139
Electricity Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues									938,374	820,306	771,857
Gross Profit									282,677	225,446	200,249
Operating Income (Loss)									68,287	31,104	(77,751)
Depreciation and amortization									28,468	35,896	47,889
Gas Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues									569,476	543,805	599,091
Gross Profit									205,063	185,559	211,623
Operating Income (Loss)									66,813	67,471	76,101
Depreciation and amortization									20,714	20,288	25,706
Water Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues									505,336	519,422	576,668
Gross Profit									172,580	145,680	202,178
Operating Income (Loss)									37,266	19,864	71,356
Depreciation and amortization									18,675	19,459	24,257
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)									(76,155)	(65,593)	(69,226)
Depreciation and amortization									$ 461	$ 350	$ 287