REVENUES: Electric utility operating revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenues [Abstract]
Revenue from contracts with customers	$ 442,631	$ 385,229	$ 860,528	$ 770,895
Alternative revenue programs and other revenues	7,188	27,498	37,590	71,170
Electric utility revenues	$ 449,819	$ 412,727	$ 898,118	$ 842,065