Business Segment Information: Information Relating to Segments Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information
Revenue	$ 407,126	$ 462,612	$ 1,739,568	$ 1,760,377
Operating income (loss)	97,771	79,479	336,170	325,221
Corporate, Non-Segment
Segment Reporting Information
Operating income (loss)	(645)	(587)	(2,275)	(2,552)
Inter-segment Revenues
Segment Reporting Information
Revenue	(4,488)	(4,345)	(13,464)	(13,058)
Operating Segments
Segment Reporting Information
Operating income (loss)	97,771	79,479	336,170	325,221
Operating Segments \| Electric Utilities
Segment Reporting Information
Revenue	237,329	258,669	649,111	669,586
Operating income (loss)	83,016	69,483	190,695	165,455
Operating Segments \| Gas Utilities
Segment Reporting Information
Revenue	174,285	208,288	1,103,921	1,103,849
Operating income (loss)	15,400	10,583	147,750	162,318
External Customers \| Operating Segments \| Electric Utilities
Segment Reporting Information
Revenue	234,490	255,741	640,595	660,800
External Customers \| Operating Segments \| Gas Utilities
Segment Reporting Information
Revenue	172,636	206,871	1,098,973	1,099,577
Intercompany Customers \| Operating Segments \| Electric Utilities
Segment Reporting Information
Revenue	2,839	2,928	8,516	8,786
Intercompany Customers \| Operating Segments \| Gas Utilities
Segment Reporting Information
Revenue	$ 1,649	$ 1,417	$ 4,948	$ 4,272