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v3.19.3.a.u2

Condensed Statements of Income and Comprehensive Income (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | $ 1,378,213 | $ 1,563,799 | $ 1,303,573 | $ 1,091,191 | $ 1,209,875 | $ 1,280,787 | $ 1,064,597 | $ 976,293 | $ 5,336,776 | $ 4,531,552 | $ 4,443,351
Operating expenses | 1,247,992 | 1,374,329 | 1,206,262 | 1,026,973 | 1,091,524 | 1,140,783 | 990,605 | 906,917 | 4,855,556 | 4,129,829 | 4,019,303
Operating income | 130,221 | 189,470 | 97,311 | 64,218 | 118,351 | 140,004 | 73,992 | 69,376 | 481,220 | 401,723 | 424,048
Other income |  |  |  |  |  |  |  |  | 15,812 | (238) | 8,767
Interest expense |  |  |  |  |  |  |  |  | 98,587 | 84,614 | 82,788
Income before income taxes |  |  |  |  |  |  |  |  | 398,445 | 316,871 | 350,027
Income taxes |  |  |  |  |  |  |  |  | 63,279 | 47,485 | 65,041
Net income from continuing operations | $ 94,804 | $ 136,128 | $ 63,145 | $ 41,089 | $ 75,982 | $ 107,369 | $ 44,075 | $ 41,960 | 335,166 | 269,386 | 284,986
Loss on redemption of preferred stock |  |  |  |  |  |  |  |  | 0 | 0 | 600
Earnings on common stock |  |  |  |  |  |  |  |  | 335,453 | 272,318 | 280,432
Comprehensive income |  |  |  |  |  |  |  |  | 331,693 | 279,269 | 279,602
MDU Resources Group, Inc. [Member] |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 0 | 628,331 | 623,693
Operating expenses |  |  |  |  |  |  |  |  | 0 | 540,125 | 520,069
Operating income |  |  |  |  |  |  |  |  | 0 | 88,206 | 103,624
Other income |  |  |  |  |  |  |  |  | 0 | 1,504 | 4,876
Interest expense |  |  |  |  |  |  |  |  | 0 | 32,761 | 31,997
Income before income taxes |  |  |  |  |  |  |  |  | 0 | 56,949 | 76,503
Income taxes |  |  |  |  |  |  |  |  | 0 | (4,259) | 13,800
Equity in earnings of subsidiaries from continuing operations |  |  |  |  |  |  |  |  | 335,166 | 208,177 | 222,283
Net income from continuing operations |  |  |  |  |  |  |  |  | 335,166 | 269,385 | 284,986
Equity in earnings (loss) of subsidiaries from discontinued operations |  |  |  |  |  |  |  |  | 287 | 2,933 | (3,783)
Loss on redemption of preferred stock |  |  |  |  |  |  |  |  |  |  | 600
Dividends declared on preferred stock |  |  |  |  |  |  |  |  |  |  | 171
Earnings on common stock |  |  |  |  |  |  |  |  | 335,453 | 272,318 | 280,432
Comprehensive income |  |  |  |  |  |  |  |  | $ 331,693 | $ 279,269 | $ 279,602

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