REVENUES: Electric utility operating revenues (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Revenues [Abstract]
Revenue from contracts with customers	$ 468,250	$ 449,313	$ 851,865	$ 860,456
Alternative revenue programs and other revenues	423	359	19,570	21,169
Electric utility revenues	$ 468,673	$ 449,672	$ 871,435	$ 881,625

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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+ Details