REVENUES: Electric utility operating revenues (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Revenues [Abstract]
Revenue from contracts with customers	$ 383,615	$ 411,142
Alternative revenue programs and other revenues	19,147	20,810
Electric utility revenues	$ 402,762	$ 431,952

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