Business Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024
Segment Reporting Information [Line Items]
Income Tax Expense (Benefit)	$ 20,368			$ 8,314			$ 62,943	$ 24,833
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	56,014			54,068			90,325	89,725
Net Income (Loss) Attributable to Parent	63,729	$ 28,749	$ 101,143	54,940	$ 41,794	$ 17,162
Segment, Expenditure, Addition to Long-Lived Assets	251,139			189,282			547,963	727,152
UTILITY OPERATING REVENUES	529,344			449,171			1,445,728	1,254,566
Fuel Costs	138,017			96,103			344,499	276,661
Cost of Goods and Services Sold	38,604			31,100			105,373	113,836
Utilities Operating Expense, Maintenance and Operations	135,041			125,849			419,957	350,309
Depreciation and amortization	93,239			85,493			271,313	248,846
Taxes other than income taxes	6,262			6,130			19,565	20,572
Allowance for equity funds used during construction	(622)			(1,485)			(2,023)	(3,585)
Interest Expense	42,211			44,198			132,794	131,681
Segment Reporting, Other Segment Item, Amount	210			(599)			982	1,688
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	76,382			62,382			153,268	114,558
Other Segments [Member]
Segment Reporting Information [Line Items]
Income Tax Expense (Benefit)	(3,498)			(2,096)			(7,709)	(6,005)
Net Income (Loss) Attributable to Parent	(6,843)			(8,631)			(23,726)	(25,495)
UTILITY OPERATING REVENUES	0			0
Utilities Operating Expense, Maintenance and Operations	156			497			374	730
Interest Expense	10,447			10,453			31,342	32,674
Segment Reporting, Other Segment Item, Amount	(262)			(223)			(281)	(1,904)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	(10,341)			(10,727)			(31,435)	(31,500)
Corporate Segment
Segment Reporting Information [Line Items]
Income Tax Expense (Benefit)	23,866			10,410			70,652	30,838
Net Income (Loss) Attributable to Parent	62,857			62,699			114,051	115,220
Segment, Expenditure, Addition to Long-Lived Assets	251,139			189,282			547,963	727,152
UTILITY OPERATING REVENUES	529,344			449,171			1,445,728	1,254,566
Fuel Costs	138,017			96,103			344,499	276,661
Cost of Goods and Services Sold	38,604			31,100			105,373	113,836
Utilities Operating Expense, Maintenance and Operations	134,885			125,352			419,583	349,579
Depreciation and amortization	93,239			85,493			271,313	248,846
Taxes other than income taxes	6,262			6,130			19,565	20,572
Allowance for equity funds used during construction	(622)			(1,485)			(2,023)	(3,585)
Interest Expense	31,764			33,745			101,452	99,007
Segment Reporting, Other Segment Item, Amount	472			(376)			1,263	3,592
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	86,723			73,109			184,703	146,058
Electricity [Member]
Segment Reporting Information [Line Items]
UTILITY OPERATING REVENUES	$ 529,344			$ 449,171			$ 1,445,728	$ 1,254,566