REVENUES: Electric utility operating revenues (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Revenues [Abstract]
Revenue from contracts with customers	$ 614,841	$ 526,424	$ 1,466,707	$ 1,386,879
Alternative revenue programs and other revenues	(7,804)	(2,875)	11,765	18,294
Electric utility revenues	$ 607,037	$ 523,549	$ 1,478,472	$ 1,405,173

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