Condensed Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenues
Revenues	$ 901,873	$ 1,042,197	$ 2,725,795	$ 2,722,872
Expenses
Total expenses	826,762	940,082	2,464,187	2,434,813
Operating income (loss)
Total operating income	75,111	102,115	261,608	288,059
Retirement defined benefits credit—other than service costs	1,256	1,039	3,561	3,528
Interest expense, net—other than on deposit liabilities and other bank borrowings	(32,629)	(26,626)	(91,259)	(75,940)
Allowance for borrowed funds used during construction	1,372	825	3,798	2,401
Allowance for equity funds used during construction	4,000	2,552	11,073	7,431
Gain on sales of equity-method investment	0	0	0	8,123
Income (loss) before income taxes	49,110	79,905	188,781	233,602
Income taxes	7,521	17,352	36,915	48,395
Net income (loss)	41,589	62,553	151,866	185,207
Preferred stock dividends of subsidiaries	471	471	1,417	1,417
Net income for common stock	$ 41,118	$ 62,082	$ 150,449	$ 183,790
Basic earnings per common share (in dollars per share)	$ 0.37	$ 0.57	$ 1.37	$ 1.68
Diluted earnings per common share (in dollars per share)	$ 0.37	$ 0.57	$ 1.37	$ 1.68
Weighted-average number of common shares outstanding (in shares)	109,728	109,470	109,606	109,421
Net effect of potentially dilutive shares (share-based compensation programs) (in shares)	189	235	326	291
Weighted-average shares assuming dilution (in shares)	109,917	109,705	109,932	109,712
Electric utility
Revenues
Revenues	$ 794,987	$ 955,971	$ 2,419,539	$ 2,483,636
Expenses
Total expenses	723,629	876,922	2,198,681	2,259,838
Operating income (loss)
Total operating income	71,358	79,049	220,858	223,798
Income (loss) before income taxes	55,415	63,712	175,391	179,771
Income taxes	11,456	13,450	38,126	37,967
Net income (loss)	43,959	50,262	137,265	141,804
Preferred stock dividends of subsidiaries	498	498	1,496	1,496
Net income for common stock	43,461	49,764	135,769	140,308
Bank
Revenues
Revenues	100,974	81,411	291,716	231,850
Expenses
Total expenses	88,415	54,311	230,769	152,797
Operating income (loss)
Total operating income	12,559	27,100	60,947	79,053
Income (loss) before income taxes	12,749	27,281	61,511	79,605
Income taxes	1,384	6,525	11,380	17,513
Net income (loss)	11,365	20,756	50,131	62,092
Preferred stock dividends of subsidiaries	0	0	0	0
Net income for common stock	11,365	20,756	50,131	62,092
Other
Revenues
Revenues	5,912	4,815	14,540	7,386
Expenses
Total expenses	14,718	8,849	34,737	22,178
Operating income (loss)
Total operating income	(8,806)	(4,034)	(20,197)	(14,792)
Income (loss) before income taxes	(19,054)	(11,088)	(48,121)	(25,774)
Income taxes	(5,319)	(2,623)	(12,591)	(7,085)
Net income (loss)	(13,735)	(8,465)	(35,530)	(18,689)
Preferred stock dividends of subsidiaries	(27)	(27)	(79)	(79)
Net income for common stock	$ (13,708)	$ (8,438)	$ (35,451)	$ (18,610)