Unaudited summarized quarterly information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Revenues
Revenues	$ 799,180	$ 833,239	$ 795,417	$ 792,014	$ 853,424	$ 800,899	$ 798,800	$ 834,380	$ 3,219,850	$ 3,287,503	$ 3,420,917
Operating income (loss)
Operating income (loss)	53,662	(149,720)	(1,661,589)	50,887	74,331	62,552	68,111	69,998	(1,706,760)	274,992	279,555
Income (loss) from continuing operations for common stock	29,166	(123,180)	(1,249,697)	21,188	45,558	29,753	34,406	36,159	(1,322,523)	145,876	161,149
Income (loss) from discontinued operations	(97,411)	18,778	(45,787)	20,934	3,231	11,365	20,204	18,562	(103,486)	53,362	79,989
Net income (loss) for common stock	$ (68,245)	$ (104,402)	$ (1,295,484)	$ 42,122	$ 48,789	$ 41,118	$ 54,610	$ 54,721	$ (1,426,009)	$ 199,238	$ 241,138
Continuing operations - Basic earnings (loss) per common share (in dollars per share)	$ 0.17	$ (1.08)	$ (11.33)	$ 0.19	$ 0.41	$ 0.27	$ 0.31	$ 0.33	$ (10.42)	$ 1.33	$ 1.47
Discontinued operations - Basic earnings (loss) per common share (in dollars per share)	(0.56)	0.16	(0.42)	0.19	0.03	0.10	0.18	0.17	(0.81)	0.49	0.73
Basic earnings (loss) per common share (in dollars per share)	(0.40)	(0.91)	(11.74)	0.38	0.44	0.37	0.50	0.50	(11.23)	1.82	2.20
Continuing operations - Diluted earnings (loss) per common share (in dollars per share)	0.17	(1.08)	(11.33)	0.19	0.41	0.27	0.31	0.33	(10.42)	1.33	1.47
Discontinued operations - Diluted earnings (loss) per common share (in dollars per share)	(0.56)	0.16	(0.42)	0.19	0.03	0.10	0.18	0.17	(0.81)	0.48	0.73
Diluted earnings (loss) per common share (in dollars per share)	$ (0.40)	$ (0.91)	$ (11.74)	$ 0.38	$ 0.44	$ 0.37	$ 0.50	$ 0.50	$ (11.23)	$ 1.81	$ 2.20
Weighted-average number of common shares outstanding (in shares)	172,466	114,358	110,303	110,218	110,134	109,728	109,573	109,514	126,927	109,739	109,434
Weighted-average shares assuming dilution (in shares)	172,466	114,358	110,303	110,476	110,301	109,917	109,780	109,825	126,927	110,038	109,778
Operating Segments
Revenues
Revenues											$ 3,420,917
Other
Revenues
Revenues	$ 3,006	$ 3,622	$ 3,086	$ 3,436	$ 3,442	$ 5,912	$ 4,609	$ 4,019	$ 13,150	$ 17,982	12,330
Operating income (loss)
Operating income (loss)	(20,129)	(45,156)	(17,149)	(12,468)	(6,969)	(8,806)	(5,514)	(5,877)	(94,902)	(27,166)	(19,636)
Income (loss) from continuing operations for common stock									(96,161)	(48,076)	(27,780)
Electric utility
Revenues
Revenues											3,408,583
Electric utility | Operating Segments
Revenues
Revenues	796,174	829,617	792,331	788,578	849,982	794,987	794,191	830,361	3,206,700	3,269,521	3,408,587
Operating income (loss)
Operating income (loss)	$ 73,791	$ (104,564)	$ (1,644,440)	$ 63,355	$ 81,300	$ 71,358	$ 73,625	$ 75,875	(1,611,858)	302,158	299,191
Income (loss) from continuing operations for common stock									$ (1,226,362)	$ 193,952	$ 188,929