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Revenue: Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 821,769	$ 630,217
Total revenues	823,570	633,432
Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7,113	6,976
Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	814,656	623,241
Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	1,801	3,215
Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	733,819	545,885
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	49,424	47,841
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10,275	11,359
Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7,392	4,845
Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	20,859	20,287
Inter-company Revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(4,248)	(4,399)
Total revenues	(4,360)	(4,491)
Inter-company Revenues | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Inter-company Revenues | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(4,248)	(4,399)
Inter-company Revenues | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(112)	(92)
Inter-company Revenues | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Inter-company Revenues | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(99)	(110)
Inter-company Revenues | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Inter-company Revenues | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Inter-company Revenues | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(4,149)	(4,289)
Electric Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	205,668	234,597
Total revenues	206,538	235,404
Electric Utilities | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7,113	6,976
Electric Utilities | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	198,555	227,621
Electric Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	870	807
Electric Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	172,806	204,280
Electric Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Electric Utilities | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10,275	11,359
Electric Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7,154	4,772
Electric Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15,433	14,186
Gas Utilities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	620,349	400,019
Total revenues	621,392	402,519
Gas Utilities | Services transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Gas Utilities | Services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	620,349	400,019
Gas Utilities | Other revenues
Disaggregation of Revenue [Line Items]
Total revenues	1,043	2,500
Gas Utilities | Retail - Electric , Natural Gas and Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	561,013	341,605
Gas Utilities | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	49,523	47,951
Gas Utilities | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Gas Utilities | Market - off-system sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	238	73
Gas Utilities | Transmission/Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 9,575	$ 10,390

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