Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Operating revenues	$ 454,542	$ 394,482
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	165,492	135,073
Utility margin	289,050	259,409
Operating and maintenance	55,861	52,794
Administrative and general	34,748	31,644
Property and other taxes	49,151	46,850
Depreciation and depletion	53,248	48,905
Operating income (loss)	96,042	79,216
Interest expense, net	(28,008)	(23,716)
Other income (expense), net	4,737	4,721
Income tax expense	(10,241)	(1,111)
Net Income	62,530	59,110
Total assets	7,280,994	6,822,035	$ 7,317,783
Capital expenditures	136,604	115,502
Operating Segments | Electricity, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	295,308	271,727
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	78,134	77,623
Utility margin	217,174	194,104
Operating and maintenance	42,413	39,501
Administrative and general	24,968	22,737
Property and other taxes	38,251	36,425
Depreciation and depletion	43,898	40,424
Operating income (loss)	67,644	55,017
Interest expense, net	(18,560)	(18,969)
Other income (expense), net	3,366	2,982
Income tax expense	(6,628)	(994)
Net Income	45,822	38,036
Total assets	5,874,061	5,523,726
Capital expenditures	120,819	98,609
Operating Segments | Natural Gas, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	159,234	122,755
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	87,358	57,450
Utility margin	71,876	65,305
Operating and maintenance	13,448	13,293
Administrative and general	9,766	8,652
Property and other taxes	10,898	10,423
Depreciation and depletion	9,350	8,481
Operating income (loss)	28,414	24,456
Interest expense, net	(3,251)	(3,390)
Other income (expense), net	1,415	1,530
Income tax expense	234	(1,382)
Net Income	26,812	21,214
Total assets	1,399,717	1,291,946
Capital expenditures	15,785	16,893
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	0	0
Utility margin	0	0
Operating and maintenance	0	0
Administrative and general	0	0
Property and other taxes	0	0
Depreciation and depletion	0	0
Operating income (loss)	0	0
Interest expense, net	0	0
Other income (expense), net	0	0
Income tax expense	0	0
Net Income	0	0
Total assets	0	0
Capital expenditures	0	0
All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	0	0
Utility margin	0	0
Operating and maintenance	0	0
Administrative and general	14	255
Property and other taxes	2	2
Depreciation and depletion	0	0
Operating income (loss)	(16)	(257)
Interest expense, net	(6,197)	(1,357)
Other income (expense), net	(44)	209
Income tax expense	(3,847)	1,265
Net Income	(10,104)	(140)
Total assets	7,216	6,363
Capital expenditures	$ 0	$ 0