Segment Information (Company's Segment Information, Continuing Operations) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 361,860			$ 348,647			$ 1,342,457	$ 988,700
Operations and maintenance expense	139,355			136,174			391,945	371,415
Purchased gas	25,488			16,744			202,538	72,934
Depreciation and amortization	74,507			69,941			221,623	186,078
Taxes other than income taxes	21,058			20,555			63,219	56,424
Operating income (loss)	101,452			105,233			463,132	301,849
Interest expense, net	51,567			49,747			153,647	131,304
Allowance for funds used during construction	(6,082)			(3,543)			(13,922)	(8,721)
Equity earnings in joint venture				3,626				3,283
Other	3,699			(4,360)			(2,016)	(3,528)
Income before income taxes	52,268			59,763			325,423	179,511
Provision for income taxes	1,765			4,031			10,317	(2,631)
Net income (loss)	50,503	$ 80,914	$ 183,689	55,732	$ 74,629	$ 51,781	315,106	182,142
Capital expenditures							675,845	554,141
Total assets	14,236,485						14,236,485		$ 13,705,277
Water [Member] | Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenues	259,859			255,725			736,389	706,008
Operations and maintenance expense	86,923			79,313			243,071	229,652
Depreciation and amortization	45,506			42,955			136,189	127,214
Taxes other than income taxes	16,291			15,906			47,756	45,292
Operating income (loss)	111,139			117,551			309,373	303,850
Interest expense, net	27,389			27,063			80,971	78,500
Allowance for funds used during construction	(5,407)			(3,082)			(13,091)	(7,905)
Other	(1,896)			110			(5,265)	477
Income before income taxes	91,053			93,460			246,758	232,778
Provision for income taxes	9,230			8,081			22,056	18,402
Net income (loss)	81,823			85,379			224,702	214,376
Capital expenditures							404,894	376,064
Total assets	8,301,201						8,301,201		7,838,034
Natural Gas [Member] | Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenues	94,752			88,880			579,429	273,798
Operations and maintenance expense	53,954			59,560			157,614	120,192
Purchased gas	20,386			14,841			183,062	68,807
Depreciation and amortization	28,194			25,793			83,905	56,026
Taxes other than income taxes	4,271			4,145			13,356	8,799
Operating income (loss)	(12,053)			(15,459)			141,492	19,974
Interest expense, net	18,406			9,333			56,125	21,260
Allowance for funds used during construction	(675)			(461)			(831)	(816)
Other	5,329			(761)			4,462	(1,516)
Income before income taxes	(35,113)			(23,570)			81,736	1,046
Provision for income taxes	(6,821)			(1,219)			(11,128)	(8,131)
Net income (loss)	(28,292)			(22,351)			92,864	9,177
Capital expenditures							269,958	134,632
Total assets	5,748,774						5,748,774		5,303,507
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	7,249			4,042			26,639	8,894
Operations and maintenance expense	(1,522)			(2,699)			(8,740)	21,571
Purchased gas	5,102			1,903			19,476	4,127
Depreciation and amortization	807			1,193			1,529	2,838
Taxes other than income taxes	496			504			2,107	2,333
Operating income (loss)	2,366			3,141			12,267	(21,975)
Interest expense, net	5,772			13,351			16,551	31,544
Equity earnings in joint venture				3,626				3,283
Other	266			(3,709)			(1,213)	(2,489)
Income before income taxes	(3,672)			(10,127)			(3,071)	(54,313)
Provision for income taxes	(644)			(2,831)			(611)	(12,902)
Net income (loss)	(3,028)			$ (7,296)			(2,460)	(41,411)
Capital expenditures							993	$ 43,445
Total assets	$ 186,510						$ 186,510		$ 563,736