CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Statement [Abstract]
OPERATING REVENUES (Note 2)	$ 951,712	$ 944,955
OPERATING EXPENSES
Fuel and purchased power	357,864	394,504
Operations and maintenance	257,578	250,080
Depreciation and amortization	210,294	191,906
Taxes other than income taxes	59,164	57,138
Other expense	20	610
Total	884,920	894,238
OPERATING INCOME	66,792	50,717
OTHER INCOME (DEDUCTIONS)
Allowance for equity funds used during construction	10,292	15,061
Pension and other postretirement non-service credits - net (Note 5)	11,568	9,865
Other income (Note 9)	30,607	6,077
Other expense (Note 9)	(7,567)	(4,131)
Total	44,900	26,872
INTEREST EXPENSE
Interest charges	99,774	88,119
Allowance for borrowed funds used during construction	(13,141)	(12,722)
Total	86,633	75,397
Income Before Income Taxes	25,059	2,192
Income Taxes	3,891	1,183
Net Income	21,168	1,009
Less: Net income attributable to noncontrolling interests (Note 6)	4,306	4,306
Net Income (Loss) Attributable to Common Shareholders	$ 16,862	$ (3,297)
Weighted-average common shares outstanding - basic (in shares)	113,621	113,358
Weighted-average common shares outstanding - diluted (in shares)	114,227	113,358
Earnings Per Weighted-Average Common Share Outstanding
Net income (loss) attributable to common shareholders - basic (in dollars per share)	$ 0.15	$ (0.03)
Net income (loss) attributable to common shareholders - diluted (in dollars per share)	$ 0.15	$ (0.03)