Information By Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 595,962	$ 486,747	$ 1,789,073	$ 1,467,421
Gross profit	197,097	165,755	553,529	501,669
Operating income (loss)	41,676	38,226	(78,209)	106,681
Total other income (expense)	(16,174)	(4,732)	(45,193)	(16,559)
Income (loss) before income taxes	25,502	33,494	(123,402)	90,122
Electricity Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	236,842	240,142	739,825	729,225
Gross profit	74,549	76,492	221,511	222,387
Operating income (loss)	25,853	17,317	52,082	52,240
Gas Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	156,747	131,780	431,518	394,691
Gross profit	55,812	46,529	139,826	147,880
Operating income (loss)	31,279	20,469	18,176	59,177
Water Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	112,584	114,825	368,415	343,505
Gross profit	35,139	42,734	110,779	131,402
Operating income (loss)	6,859	15,032	3,973	40,702
Networks Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	89,789	0	249,315	0
Gross profit	31,597	0	81,413	0
Operating income (loss)	(15,624)	0	(119,353)	0
Corporate Unallocated [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(6,691)	(14,592)	(33,087)	(45,438)
Product [Member]
Segment Reporting Information [Line Items]
Revenues	525,716	433,984	1,578,740	1,321,062
Product [Member] | Electricity Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	198,026	199,784	624,139	620,958
Product [Member] | Gas Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	148,660	124,556	408,300	372,555
Product [Member] | Water Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	106,653	109,644	350,814	327,549
Product [Member] | Networks Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	72,377	0	195,487	0
Service [Member]
Segment Reporting Information [Line Items]
Revenues	70,246	52,763	210,333	146,359
Service [Member] | Electricity Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	38,816	40,358	115,686	108,267
Service [Member] | Gas Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	8,087	7,224	23,218	22,136
Service [Member] | Water Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	5,931	5,181	17,601	15,956
Service [Member] | Networks Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	$ 17,412	$ 0	$ 53,828	$ 0