Derivative Instruments - Realized and unrealized gains (losses) on derivative instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Gains and (losses) on derivative instruments
Net unrealized gains on derivative instruments			$ 47,054		$ 131,804
Natural gas swaps
Gains and (losses) on derivative instruments
Gains	$ 643	$ 57,639	783	$ 108,280
Losses	(2,935)	(2,995)	(19,539)	(3,277)
Total	$ (2,292)	$ 54,644	(18,756)	$ 105,003
Natural gas swaps | Regulatory liability
Gains and (losses) on derivative instruments
Net unrealized gains on derivative instruments			$ 47,054		$ 131,804