Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Operating revenues	$ 335,068	$ 325,955	$ 1,052,554	$ 1,024,975
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	108,920	98,659	338,994	311,137
Utility margin	226,148	227,296	713,560	713,838
Operating and maintenance	54,654	56,002	160,785	159,317
Administrative and general	28,146	24,946	87,010	79,596
Property and other taxes	46,466	43,572	140,209	138,337
Depreciation and depletion	48,588	47,112	145,705	140,896
Operating income (loss)	48,294	55,664	179,851	195,692
Interest expense, net	(25,332)	(23,283)	(73,081)	(70,266)
Other income (expense), net	4,157	5,326	11,791	13,932
Income tax benefit (expense)	249	(2,511)	(2,297)	(3,854)
Net Income	27,368	35,196	116,264	135,504
Total assets	7,114,213	6,666,630	7,114,213	6,666,630	$ 6,780,443
Capital expenditures	151,901	128,966	386,339	311,160
Operating Segments | Electricity, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	292,270	287,473	807,415	798,984
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	95,553	89,375	230,872	218,802
Utility margin	196,717	198,098	576,543	580,182
Operating and maintenance	40,914	44,319	121,237	122,013
Administrative and general	20,739	16,302	63,591	54,398
Property and other taxes	36,353	34,066	109,204	108,050
Depreciation and depletion	40,647	38,634	121,256	115,858
Operating income (loss)	58,064	64,777	161,255	179,863
Interest expense, net	(18,225)	(20,429)	(56,031)	(62,007)
Other income (expense), net	2,944	3,348	7,245	8,392
Income tax benefit (expense)	(1,006)	(1,680)	(2,790)	(2,369)
Net Income	41,777	46,016	109,679	123,879
Total assets	5,741,879	5,370,432	5,741,879	5,370,432
Capital expenditures	122,522	102,188	312,804	253,588
Operating Segments | Natural Gas, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	42,798	38,482	245,139	225,991
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	13,367	9,284	108,122	92,335
Utility margin	29,431	29,198	137,017	133,656
Operating and maintenance	13,740	11,683	39,548	37,304
Administrative and general	7,934	8,746	23,757	23,569
Property and other taxes	10,110	9,504	30,998	30,281
Depreciation and depletion	7,941	8,478	24,449	25,038
Operating income (loss)	(10,294)	(9,213)	18,265	17,464
Interest expense, net	(3,238)	(1,640)	(9,951)	(4,550)
Other income (expense), net	1,727	2,016	4,669	4,035
Income tax benefit (expense)	1,119	725	(1,263)	(1,505)
Net Income	(10,686)	(8,112)	11,720	15,444
Total assets	1,365,896	1,291,144	1,365,896	1,291,144
Capital expenditures	29,379	26,778	73,535	57,572
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	0	0	0	0
Utility margin	0	0	0	0
Operating and maintenance	0	0	0	0
Administrative and general	0	0	0	0
Property and other taxes	0	0	0	0
Depreciation and depletion	0	0	0	0
Operating income (loss)	0	0	0	0
Interest expense, net	0	0	0	0
Other income (expense), net	0	0	0	0
Income tax benefit (expense)	0	0	0	0
Net Income	0	0	0	0
Total assets	0	0	0	0
Capital expenditures	0	0	0	0
All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	0	0	0	0
Utility margin	0	0	0	0
Operating and maintenance	0	0	0	0
Administrative and general	(527)	(102)	(338)	1,629
Property and other taxes	3	2	7	6
Depreciation and depletion	0	0	0	0
Operating income (loss)	524	100	331	(1,635)
Interest expense, net	(3,869)	(1,214)	(7,099)	(3,709)
Other income (expense), net	(514)	(38)	(123)	1,505
Income tax benefit (expense)	136	(1,556)	1,756	20
Net Income	(3,723)	(2,708)	(5,135)	(3,819)
Total assets	6,438	5,054	6,438	5,054
Capital expenditures	$ 0	$ 0	$ 0	$ 0