Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Operating revenues	$ 394,482	$ 400,803
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	135,073	144,513
Utility margin	259,409	256,290
Operating and maintenance	52,794	51,797
Administrative and general	31,644	29,055
Property and other taxes	46,850	47,478
Depreciation and depletion	48,905	46,975
Operating income (loss)	79,216	80,985
Interest expense, net	(23,716)	(23,510)
Other income, net	4,721	5,574
Income tax (expense) benefit	(1,111)	22
Net Income	59,110	63,071
Total assets	(6,822,035)	(6,502,813)	$ (6,780,443)
Capital expenditures	115,502	77,854
Operating Segments | Electricity, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	271,727	270,071
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	77,623	80,188
Utility margin	194,104	189,883
Operating and maintenance	39,501	38,206
Administrative and general	22,737	19,549
Property and other taxes	36,425	37,027
Depreciation and depletion	40,424	38,684
Operating income (loss)	55,017	56,417
Interest expense, net	(18,969)	(20,729)
Other income, net	2,982	2,829
Income tax (expense) benefit	(994)	115
Net Income	38,036	38,632
Total assets	(5,523,726)	(5,220,632)
Capital expenditures	98,609	68,940
Operating Segments | Electricity, US Regulated | Revision of Prior Period, Error Correction, Adjustment
Segment Reporting Information [Line Items]
Total assets	(484,800)
Operating Segments | Natural Gas, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	122,755	130,732
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	57,450	64,325
Utility margin	65,305	66,407
Operating and maintenance	13,293	13,591
Administrative and general	8,652	7,588
Property and other taxes	10,423	10,449
Depreciation and depletion	8,481	8,291
Operating income (loss)	24,456	26,488
Interest expense, net	(3,390)	(1,488)
Other income, net	1,530	983
Income tax (expense) benefit	(1,382)	(2,022)
Net Income	21,214	23,961
Total assets	(1,291,946)	(1,270,686)
Capital expenditures	16,893	8,914
Operating Segments | Natural Gas, US Regulated | Revision of Prior Period, Error Correction, Adjustment
Segment Reporting Information [Line Items]
Total assets	484,800
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, net	0	0
Income tax (expense) benefit	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	255	1,918
Property and other taxes	2	2
Depreciation and depletion	0	0
Operating income (loss)	(257)	(1,920)
Interest expense, net	(1,357)	(1,293)
Other income, net	209	1,762
Income tax (expense) benefit	1,265	1,929
Net Income	(140)	478
Total assets	(6,363)	(11,495)
Capital expenditures	$ 0	$ 0