REVENUES: Electric utility operating revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue from contracts with customers	$ 357,461	$ 310,971	$ 648,787	$ 581,155
Alternative revenue programs and other revenues	1,597	6,695	25,838	26,999
Electric utility revenues	$ 359,058	$ 317,666	$ 674,625	$ 608,154