Revenue: Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Revenue from contracts with customers	$ 405,136	$ 470,324	$ 1,317,191	$ 1,292,093
Revenue	411,283	474,195	1,332,442	1,297,765
Retail - Electric , Natural Gas and Coal
Revenue from contracts with customers	331,153	398,106	1,141,601	1,131,925
Transportation
Revenue from contracts with customers	35,798	34,567	88,526	83,991
Wholesale
Revenue from contracts with customers	5,739	8,428	15,137	18,703
Market - off-system sales
Revenue from contracts with customers	8,407	8,844	24,812	16,236
Transmission/Other
Revenue from contracts with customers	24,039	20,379	47,115	41,238
Other revenues
Revenue	6,147	3,871	15,251	5,672
Services transferred at a point in time
Revenue from contracts with customers	7,844	6,671	16,501	13,784
Services transferred over time
Revenue from contracts with customers	397,292	463,653	1,300,690	1,278,309
Electric Utilities
Revenue from contracts with customers	189,706	201,309	407,535	406,977
Revenue	193,073	204,379	411,782	410,917
Electric Utilities \| Retail - Electric , Natural Gas and Coal
Revenue from contracts with customers	156,372	169,032	331,275	341,838
Electric Utilities \| Transportation
Revenue from contracts with customers	0	0	0	0
Electric Utilities \| Wholesale
Revenue from contracts with customers	5,739	8,428	15,137	18,703
Electric Utilities \| Market - off-system sales
Revenue from contracts with customers	8,364	8,666	24,488	15,820
Electric Utilities \| Transmission/Other
Revenue from contracts with customers	19,231	15,183	36,635	30,616
Electric Utilities \| Other revenues
Revenue	3,367	3,070	4,247	3,940
Electric Utilities \| Services transferred at a point in time
Revenue from contracts with customers	7,844	6,671	16,501	13,784
Electric Utilities \| Services transferred over time
Revenue from contracts with customers	181,862	194,638	391,034	393,193
Gas Utilities
Revenue from contracts with customers	219,940	273,263	918,632	893,612
Revenue	222,720	274,169	929,636	895,561
Gas Utilities \| Retail - Electric , Natural Gas and Coal
Revenue from contracts with customers	174,781	229,074	810,326	790,087
Gas Utilities \| Transportation
Revenue from contracts with customers	35,913	34,667	88,756	84,190
Gas Utilities \| Wholesale
Revenue from contracts with customers	0	0	0	0
Gas Utilities \| Market - off-system sales
Revenue from contracts with customers	43	178	324	416
Gas Utilities \| Transmission/Other
Revenue from contracts with customers	9,203	9,344	19,226	18,919
Gas Utilities \| Other revenues
Revenue	2,780	906	11,004	1,949
Gas Utilities \| Services transferred at a point in time
Revenue from contracts with customers	0	0	0	0
Gas Utilities \| Services transferred over time
Revenue from contracts with customers	219,940	273,263	918,632	893,612
Inter-segment Revenues
Revenue from contracts with customers	(4,510)	(4,248)	(8,976)	(8,496)
Revenue	(4,510)	(4,353)	(8,976)	(8,713)
Inter-segment Revenues \| Retail - Electric , Natural Gas and Coal
Revenue from contracts with customers	0	0	0	0
Inter-segment Revenues \| Transportation
Revenue from contracts with customers	(115)	(100)	(230)	(199)
Inter-segment Revenues \| Wholesale
Revenue from contracts with customers	0	0	0	0
Inter-segment Revenues \| Market - off-system sales
Revenue from contracts with customers	0	0	0	0
Inter-segment Revenues \| Transmission/Other
Revenue from contracts with customers	(4,395)	(4,148)	(8,746)	(8,297)
Inter-segment Revenues \| Other revenues
Revenue	0	(105)	0	(217)
Inter-segment Revenues \| Services transferred at a point in time
Revenue from contracts with customers	0	0	0	0
Inter-segment Revenues \| Services transferred over time
Revenue from contracts with customers	$ (4,510)	$ (4,248)	$ (8,976)	$ (8,496)