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Business Segment Information: Information Relating to Segment Statement of Income (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | $ 344,312 |  |  | $ 323,745 |  |  | $ 1,198,714 | $ 1,251,461
Revenues | 346,590 |  |  | 325,548 |  |  | 1,210,554 | 1,257,246
Operating income | 82,234 |  |  | 70,551 |  |  | 302,352 | 284,683
Interest expense, net | (36,041) |  |  | (33,487) |  |  | (107,039) | (102,469)
Impairment of investment | 0 |  | $ (6,900) | (19,741) |  |  | (6,859) | (19,741)
Other income (expense), net | (1,193) |  |  | 580 |  |  | (703) | 55
Income tax (expense) | (4,651) |  |  | (2,508) |  |  | (25,484) | (22,078)
Net income | 40,349 | $ 24,694 | $ 97,224 | 15,395 | $ 17,693 | $ 107,362 | 162,267 | 140,450
Net income attributable to noncontrolling interest | (4,066) |  |  | (3,655) |  |  | (11,844) | (10,319)
Net income available for common stock | 36,283 |  |  | 11,740 |  |  | 150,423 | 130,131
Inter-company Revenues |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | (39,899) |  |  | (28,449) |  |  | (117,083) | (82,796)
Revenues | (39,935) |  |  | (37,943) |  |  | (117,902) | (111,502)
Consolidation, Eliminations |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 0 |  |  | 0 |  |  | 0 | 0
Corporate and Other |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Operating income | (239) |  |  | (34) |  |  | (108) | (439)
Electric Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 200,618 |  |  | 191,150 |  |  | 536,107 | 538,200
Revenues | 200,842 |  |  | 191,384 |  |  | 538,181 | 540,665
Operating income | 52,083 |  |  | 50,653 |  |  | 121,726 | 125,219
Gas Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 142,876 |  |  | 129,933 |  |  | 658,539 | 706,158
Revenues | 143,929 |  |  | 130,744 |  |  | 665,812 | 707,293
Operating income | 18,147 |  |  | 4,736 |  |  | 139,253 | 116,607
Power Generation |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 26,049 |  |  | 16,119 |  |  | 77,234 | 46,650
Revenues | 26,518 |  |  | 25,811 |  |  | 78,606 | 75,764
Operating income | 8,738 |  |  | 11,822 |  |  | 31,489 | 33,945
Mining |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 14,668 |  |  | 14,992 |  |  | 43,917 | 43,249
Revenues | 15,236 |  |  | 15,552 |  |  | 45,857 | 45,026
Operating income | 3,505 |  |  | 3,374 |  |  | 9,992 | 9,351
Other Revenues |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 2,278 |  |  | 1,803 |  |  | 11,840 | 5,785
Other Revenues | Inter-company Revenues |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | (36) |  |  | (9,494) |  |  | (819) | (28,706)
Other Revenues | Consolidation, Eliminations |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 0 |  |  | 0 |  |  | 0 | 0
Other Revenues | Electric Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 224 |  |  | 234 |  |  | 2,074 | 2,465
Other Revenues | Gas Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 1,053 |  |  | 811 |  |  | 7,273 | 1,135
Other Revenues | Power Generation |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 469 |  |  | 9,692 |  |  | 1,372 | 29,114
Other Revenues | Mining |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 568 |  |  | 560 |  |  | 1,940 | 1,777
External Operating Revenue |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 344,312 |  |  | 323,745 |  |  | 1,198,714 | 1,251,461
External Operating Revenue | Electric Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 194,941 |  |  | 185,811 |  |  | 518,641 | 521,614
External Operating Revenue | Gas Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 141,275 |  |  | 129,385 |  |  | 655,386 | 704,188
External Operating Revenue | Power Generation |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 1,528 |  |  | 1,703 |  |  | 4,625 | 5,725
External Operating Revenue | Mining |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 6,568 |  |  | 6,846 |  |  | 20,062 | 19,934
External Operating Revenue | Other Revenues |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 2,278 |  |  | 1,803 |  |  | 11,840 | 5,785
External Operating Revenue | Other Revenues | Electric Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 224 |  |  | 234 |  |  | 2,074 | 2,465
External Operating Revenue | Other Revenues | Gas Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 863 |  |  | 810 |  |  | 7,083 | 1,134
External Operating Revenue | Other Revenues | Power Generation |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 414 |  |  | 531 |  |  | 1,206 | 1,401
External Operating Revenue | Other Revenues | Mining |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 777 |  |  | 228 |  |  | 1,477 | 785
Inter-company Operating Revenue | Electric Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 5,677 |  |  | 5,339 |  |  | 17,466 | 16,586
Inter-company Operating Revenue | Gas Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 1,601 |  |  | 549 |  |  | 3,153 | 1,971
Inter-company Operating Revenue | Power Generation |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 24,521 |  |  | 14,415 |  |  | 72,609 | 40,924
Inter-company Operating Revenue | Mining |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenue from contracts with customers | 8,100 |  |  | 8,146 |  |  | 23,855 | 23,315
Inter-company Operating Revenue | Other Revenues | Electric Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 0 |  |  | 0 |  |  | 0 | 0
Inter-company Operating Revenue | Other Revenues | Gas Utilities |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 190 |  |  | 0 |  |  | 190 | 0
Inter-company Operating Revenue | Other Revenues | Power Generation |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | 55 |  |  | 9,162 |  |  | 166 | 27,714
Inter-company Operating Revenue | Other Revenues | Mining |  |  |  |  |  |  |  |
Segment Reporting Information |  |  |  |  |  |  |  |
Revenues | $ (209) |  |  | $ 332 |  |  | $ 463 | $ 992

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