XML 150 R134.htm IDEA: XBRL DOCUMENT v3.10.0.1
Condensed Statements of Income and Comprehensive Income (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]                      
Operating revenues $ 1,209,875 $ 1,280,787 $ 1,064,597 $ 976,293 $ 1,165,239 $ 1,272,548 $ 1,067,639 $ 937,925 $ 4,531,552 $ 4,443,351 $ 4,128,828
Operating expenses 1,091,524 1,140,783 990,605 906,917 1,040,957 1,117,228 988,979 872,139 4,129,829 4,019,303 3,719,919
Operating income 118,351 140,004 73,992 69,376 124,282 155,320 78,660 65,786 401,723 424,048 408,909
Other income                 (238) 8,767 5,167
Interest expense                 84,614 82,788 87,848
Income before income taxes                 316,871 350,027 326,228
Income taxes                 47,485 65,041 93,132
Income from continuing operations $ 75,982 $ 107,369 $ 44,075 $ 41,960 $ 115,394 $ 89,549 $ 44,405 $ 35,638 269,386 284,986 233,096
Loss on redemption of preferred stocks                 0 600 0
Earnings on common stock                 272,318 280,432 63,748
Comprehensive income                 279,269 279,602 65,848
MDU Resources Group, Inc. [Member]                      
Condensed Financial Statements, Captions [Line Items]                      
Operating revenues                 628,331 623,693 561,266
Operating expenses                 540,125 520,069 469,853
Operating income                 88,206 103,624 91,413
Other income                 1,504 4,876 2,282
Interest expense                 32,761 31,997 31,519
Income before income taxes                 56,949 76,503 62,176
Income taxes                 (4,259) 13,800 6,355
Equity in earnings of subsidiaries from continuing operations                 208,177 222,283 177,275
Income from continuing operations                 269,385 284,986 233,096
Equity in earnings (loss) of subsidiaries from discontinued operations attributable to the Company                 2,933 (3,783) (168,663)
Loss on redemption of preferred stocks                 0 600 0
Dividends declared on preferred stocks                 0 171 685
Earnings on common stock                 272,318 280,432 63,748
Comprehensive income                 $ 279,269 $ 279,602 $ 65,848