Revenue: Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue from contracts with customers	$ 2,542,856	$ 1,930,834	$ 1,680,804
Revenue	2,551,816	1,949,102	1,696,941
Retail - Electric , Natural Gas and Coal
Revenue from contracts with customers	2,193,000	1,625,173	1,402,824
Transportation
Revenue from contracts with customers	172,862	157,625	154,055
Wholesale
Revenue from contracts with customers	44,832	30,848	24,845
Market - off-system sales
Revenue from contracts with customers	49,407	42,078	15,772
Transmission/Other
Revenue from contracts with customers	82,755	75,110	83,308
Other revenues
Revenue	8,960	18,268	16,137
Services transferred at a point in time
Revenue from contracts with customers	30,454	27,141	27,089
Services transferred over time
Revenue from contracts with customers	2,512,402	1,903,693	1,653,715
Electric Utilities
Revenue from contracts with customers	894,614	836,923	732,681
Revenue	900,162	842,258	738,857
Electric Utilities \| Retail - Electric , Natural Gas and Coal
Revenue from contracts with customers	739,734	711,448	636,902
Electric Utilities \| Transportation
Revenue from contracts with customers	0	0	0
Electric Utilities \| Wholesale
Revenue from contracts with customers	44,832	30,848	24,845
Electric Utilities \| Market - off-system sales
Revenue from contracts with customers	48,578	41,682	15,512
Electric Utilities \| Transmission/Other
Revenue from contracts with customers	61,470	52,945	55,422
Electric Utilities \| Other revenues
Revenue	5,548	5,335	6,176
Electric Utilities \| Services transferred at a point in time
Revenue from contracts with customers	30,454	27,141	27,089
Electric Utilities \| Services transferred over time
Revenue from contracts with customers	864,160	809,782	705,592
Gas Utilities
Revenue from contracts with customers	1,665,249	1,111,539	964,421
Revenue	1,669,090	1,124,865	974,670
Gas Utilities \| Retail - Electric , Natural Gas and Coal
Revenue from contracts with customers	1,453,266	913,725	765,922
Gas Utilities \| Transportation
Revenue from contracts with customers	173,275	158,053	154,581
Gas Utilities \| Wholesale
Revenue from contracts with customers	0	0	0
Gas Utilities \| Market - off-system sales
Revenue from contracts with customers	829	396	260
Gas Utilities \| Transmission/Other
Revenue from contracts with customers	37,879	39,365	43,658
Gas Utilities \| Other revenues
Revenue	3,841	13,326	10,249
Gas Utilities \| Services transferred at a point in time
Revenue from contracts with customers	0	0	0
Gas Utilities \| Services transferred over time
Revenue from contracts with customers	1,665,249	1,111,539	964,421
Intercompany Eliminations
Revenue from contracts with customers	(17,007)	(17,628)	(16,298)
Revenue	(17,436)	(18,021)	(16,586)
Intercompany Eliminations \| Retail - Electric , Natural Gas and Coal
Revenue from contracts with customers	0	0	0
Intercompany Eliminations \| Transportation
Revenue from contracts with customers	(413)	(428)	(526)
Intercompany Eliminations \| Wholesale
Revenue from contracts with customers	0	0	0
Intercompany Eliminations \| Market - off-system sales
Revenue from contracts with customers	0	0	0
Intercompany Eliminations \| Transmission/Other
Revenue from contracts with customers	(16,594)	(17,200)	(15,772)
Intercompany Eliminations \| Other revenues
Revenue	(429)	(393)	(288)
Intercompany Eliminations \| Services transferred at a point in time
Revenue from contracts with customers	0	0	0
Intercompany Eliminations \| Services transferred over time
Revenue from contracts with customers	$ (17,007)	$ (17,628)	$ (16,298)