Information By Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Product revenues	$ 515,914	$ 454,713	$ 1,053,024	$ 887,078
Service revenues	69,976	48,369	140,087	93,596
Revenues	585,890	503,082	1,193,111	980,674
Gross profit	176,577	178,277	356,432	335,914
Operating income (loss)	20,563	37,628	(119,885)	68,455
Total other income (expense)	(13,009)	(6,061)	(29,019)	(11,827)
Income (loss) before income taxes	7,554	31,567	(148,904)	56,628
Electricity Operating Segment [Member]
Segment Reporting Information [Line Items]
Product revenues	212,236	215,271	426,113	421,174
Service revenues	38,342	35,061	76,870	67,909
Revenues	250,578	250,332	502,983	489,083
Gross profit	76,987	78,645	146,962	145,895
Operating income (loss)	28,997	17,839	26,229	34,923
Gas Operating Segment [Member]
Segment Reporting Information [Line Items]
Product revenues	129,397	130,872	259,640	247,999
Service revenues	7,635	7,828	15,131	14,912
Revenues	137,032	138,700	274,771	262,911
Gross profit	40,543	50,536	84,014	101,351
Operating income (loss)	15,245	16,977	(13,103)	38,708
Water Operating Segment [Member]
Segment Reporting Information [Line Items]
Product revenues	118,574	108,570	244,161	217,905
Service revenues	6,063	5,480	11,670	10,775
Revenues	124,637	114,050	255,831	228,680
Gross profit	37,835	49,096	75,640	88,668
Operating income (loss)	8,824	16,866	(2,886)	25,670
Networks Operating Segment [Member]
Segment Reporting Information [Line Items]
Product revenues	55,707	0	123,110	0
Service revenues	17,936	0	36,416	0
Revenues	73,643	0	159,526	0
Gross profit	21,212	0	49,816	0
Operating income (loss)	(28,219)	0	(103,729)	0
Corporate Unallocated [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	$ (4,284)	$ (14,054)	$ (26,396)	$ (30,846)