Segment Information Information By Segment (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 496,448	$ 469,528	$ 470,811	$ 446,746	$ 510,521	$ 482,352	$ 482,314	$ 472,429	$ 917,557	$ 954,743	$ 1,387,085	$ 1,437,095	$ 1,883,533	$ 1,947,616	$ 1,938,025
Gross profit	$ 152,419	147,290	118,554	138,422	$ 155,241	145,299	160,687	152,823	256,976	313,510	404,266	458,809	556,685	614,050	614,768
Operating Income (Loss)		26,940	(3,968)	13,496		10,806	30,877	5,463	9,528	36,340	36,468	47,146	52,846	480	(139,863)
Total other income (expense)		(3,738)	(5,548)	(2,613)		(4,419)	(4,233)	(5,316)	(8,161)	(9,549)	(11,899)	(13,968)	(15,744)	(18,745)	(13,537)
Income (loss) before income taxes		$ 23,202	$ (9,516)	10,883		$ 6,387	$ 26,644	147	1,367	26,791	24,569	33,178	37,102	(18,265)	(153,400)
Depreciation and amortization				$ 19,355				$ 25,187	$ 38,792	$ 50,201	$ 57,790	$ 74,827	75,993	98,139	99,246
Electricity Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues													820,306	771,857	825,391
Gross profit													225,446	200,249	219,852
Operating Income (Loss)													31,104	(77,751)	(237,279)
Depreciation and amortization													35,896	47,889	46,510
Gas Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues													543,805	599,091	570,450
Gross profit													185,559	211,623	207,577
Operating Income (Loss)													67,471	76,101	82,176
Depreciation and amortization													20,288	25,706	27,671
Water Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues													519,422	576,668	542,184
Gross profit													145,680	202,178	187,339
Operating Income (Loss)													19,864	71,356	62,015
Depreciation and amortization													19,459	24,257	24,818
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)													(65,593)	(69,226)	(46,775)
Depreciation and amortization													$ 350	$ 287	$ 247