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Revenue: Disaggregation of Revenue (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | $ 344,312 | $ 323,745 | $ 1,198,714 | $ 1,251,461
Total revenues | 346,590 | 325,548 | 1,210,554 | 1,257,246
Services transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 6,568 | 6,846 | 20,062 | 19,934
Services transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 337,744 | 316,899 | 1,178,652 | 1,231,527
Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 2,278 | 1,803 | 11,840 | 5,785
Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 270,440 | 258,870 | 993,219 | 1,043,058
Transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 38,057 | 28,824 | 112,680 | 101,256
Wholesale |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 7,453 | 9,915 | 19,572 | 29,061
Market - off-system sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 7,667 | 5,103 | 12,014 | 12,062
Transmission/Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 20,695 | 21,033 | 61,229 | 66,024
Inter-company Revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (39,899) | (28,449) | (117,083) | (82,796)
Total revenues | (39,935) | (37,943) | (117,902) | (111,502)
Inter-company Revenues | Services transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (8,100) | (8,146) | (23,855) | (23,315)
Inter-company Revenues | Services transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (31,799) | (20,303) | (93,228) | (59,481)
Inter-company Revenues | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | (36) | (9,494) | (819) | (28,706)
Inter-company Revenues | Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (8,100) | (8,146) | (23,855) | (23,315)
Inter-company Revenues | Transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (139) | (195) | (416) | (903)
Inter-company Revenues | Wholesale |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (24,521) | (14,414) | (72,609) | (40,923)
Inter-company Revenues | Market - off-system sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (1,904) | (1,488) | (6,123) | (5,047)
Inter-company Revenues | Transmission/Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | (5,235) | (4,206) | (14,080) | (12,608)
Electric Utilities |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 200,618 | 191,150 | 536,107 | 538,200
Total revenues | 200,842 | 191,384 | 538,181 | 540,665
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 | 200,618 | 191,150 | 536,107 | 538,200
Electric Utilities | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 224 | 234 | 2,074 | 2,465
Electric Utilities | Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 169,505 | 162,214 | 459,949 | 455,409
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 | 5,925 | 8,210 | 14,947 | 23,334
Electric Utilities | Market - off-system sales |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 9,535 | 6,452 | 17,940 | 16,592
Electric Utilities | Transmission/Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 15,653 | 14,274 | 43,271 | 42,865
Gas Utilities |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 142,876 | 129,933 | 658,539 | 706,158
Total revenues | 143,929 | 130,744 | 665,812 | 707,293
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 | 142,876 | 129,933 | 658,539 | 706,158
Gas Utilities | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 1,053 | 811 | 7,273 | 1,135
Gas Utilities | Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 94,367 | 89,810 | 513,208 | 567,715
Gas Utilities | Transportation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 38,196 | 29,019 | 113,096 | 102,159
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 | 36 | 139 | 197 | 517
Gas Utilities | Transmission/Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 10,277 | 10,965 | 32,038 | 35,767
Power Generation |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 26,049 | 16,119 | 77,234 | 46,650
Total revenues | 26,518 | 25,811 | 78,606 | 75,764
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 | 26,049 | 16,119 | 77,234 | 46,650
Power Generation | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 469 | 9,692 | 1,372 | 29,114
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 | 26,049 | 16,119 | 77,234 | 46,650
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 | 14,668 | 14,992 | 43,917 | 43,249
Total revenues | 15,236 | 15,552 | 45,857 | 45,026
Mining | Services transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 14,668 | 14,992 | 43,917 | 43,249
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 | 568 | 560 | 1,940 | 1,777
Mining | Retail - Electric , Natural Gas and Coal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contracts with customers | 14,668 | 14,992 | 43,917 | 43,249
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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