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Revenue: Disaggregation of Revenue (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | $ 378,653 | $ 344,312 | $ 1,377,293 | $ 1,198,714
Total revenues | 380,590 | 346,590 | 1,386,594 | 1,210,554
Services transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 6,968 | 6,568 | 20,658 | 20,062
Services transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 371,685 | 337,744 | 1,356,635 | 1,178,652
Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 1,937 | 2,278 | 9,301 | 11,840
Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 302,858 | 270,440 | 1,158,968 | 993,219
Transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 37,541 | 38,057 | 116,922 | 112,680
Wholesale |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 6,189 | 7,453 | 20,794 | 19,572
Market - off-system sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 13,586 | 7,667 | 25,784 | 12,014
Transmission/Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 18,479 | 20,695 | 54,825 | 61,229
Inter-company Revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (39,616) | (39,899) | (117,167) | (117,083)
Total revenues | (40,104) | (39,935) | (118,622) | (117,902)
Inter-company Revenues | Services transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (8,846) | (8,100) | (23,093) | (23,855)
Inter-company Revenues | Services transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (30,770) | (31,799) | (94,074) | (93,228)
Inter-company Revenues | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | (488) | (36) | (1,455) | (819)
Inter-company Revenues | Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (8,846) | (8,100) | (23,093) | (23,855)
Inter-company Revenues | Transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (110) | (139) | (329) | (416)
Inter-company Revenues | Wholesale |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (23,725) | (24,521) | (71,656) | (72,609)
Inter-company Revenues | Market - off-system sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (1,638) | (1,904) | (6,197) | (6,123)
Inter-company Revenues | Transmission/Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (5,297) | (5,235) | (15,892) | (14,080)
Electric Utilities |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 212,900 | 200,618 | 622,825 | 536,107
Total revenues | 213,103 | 200,842 | 625,444 | 538,181
Electric Utilities | Services transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Electric Utilities | Services transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 212,900 | 200,618 | 622,825 | 536,107
Electric Utilities | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 203 | 224 | 2,619 | 2,074
Electric Utilities | Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 179,982 | 169,505 | 536,952 | 459,949
Electric Utilities | Transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Electric Utilities | Wholesale |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 3,856 | 5,925 | 12,788 | 14,947
Electric Utilities | Market - off-system sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 15,149 | 9,535 | 31,746 | 17,940
Electric Utilities | Transmission/Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 13,913 | 15,653 | 41,339 | 43,271
Gas Utilities |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 163,497 | 142,876 | 748,222 | 658,539
Total revenues | 164,683 | 143,929 | 753,252 | 665,812
Gas Utilities | Services transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Gas Utilities | Services transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 163,497 | 142,876 | 748,222 | 658,539
Gas Utilities | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 1,186 | 1,053 | 5,030 | 7,273
Gas Utilities | Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 115,908 | 94,367 | 601,358 | 513,208
Gas Utilities | Transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 37,651 | 38,196 | 117,251 | 113,096
Gas Utilities | Wholesale |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Gas Utilities | Market - off-system sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 75 | 36 | 235 | 197
Gas Utilities | Transmission/Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 9,863 | 10,277 | 29,378 | 32,038
Power Generation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 26,058 | 26,049 | 79,662 | 77,234
Total revenues | 26,520 | 26,518 | 81,031 | 78,606
Power Generation | Services transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Power Generation | Services transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 26,058 | 26,049 | 79,662 | 77,234
Power Generation | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 462 | 469 | 1,369 | 1,372
Power Generation | Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Power Generation | Transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Power Generation | Wholesale |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 26,058 | 26,049 | 79,662 | 77,234
Power Generation | Market - off-system sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Power Generation | Transmission/Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Mining |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 15,814 | 14,668 | 43,751 | 43,917
Total revenues | 16,388 | 15,236 | 45,489 | 45,857
Mining | Services transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 15,814 | 14,668 | 43,751 | 43,917
Mining | Services transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Mining | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 574 | 568 | 1,738 | 1,940
Mining | Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 15,814 | 14,668 | 43,751 | 43,917
Mining | Transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Mining | Wholesale |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Mining | Market - off-system sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 0 | 0 | 0 | 0
Mining | Transmission/Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | $ 0 | $ 0 | $ 0 | $ 0

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