Consolidated Statements Of Operations And Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Consolidated Statements Of Operations And Comprehensive Income [Abstract]
Operating revenues	$ 361,860	$ 348,647	$ 1,342,457	$ 988,700
Operating expenses:
Operations and maintenance	139,355	136,174	391,945	371,415
Purchased gas	25,488	16,744	202,538	72,934
Depreciation	72,606	68,175	217,007	181,666
Amortization	1,901	1,766	4,616	4,412
Taxes other than income taxes	21,058	20,555	63,219	56,424
Total operating expenses	260,408	243,414	879,325	686,851
Operating income	101,452	105,233	463,132	301,849
Other expense (income):
Interest expense	52,132	49,861	154,937	136,650
Interest income	(565)	(114)	(1,290)	(5,346)
Allowance for funds used during construction	(6,082)	(3,543)	(13,922)	(8,721)
Gain on sale of other assets	(320)	(233)	(623)	(358)
Equity loss in joint venture		3,626		3,283
Other	4,019	(4,127)	(1,393)	(3,170)
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	50,503	55,732	315,106	182,142
Comprehensive income	$ 50,503	$ 55,732	$ 315,106	$ 182,142
Net income per common share:
Basic	$ 0.20	$ 0.22	$ 1.23	$ 0.73
Diluted	$ 0.19	$ 0.22	$ 1.23	$ 0.71
Average common shares outstanding during the period:
Basic	258,773	254,280	256,051	248,212
Diluted	259,437	255,162	256,763	255,139