Condensed Statements of Cash Flows (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Operating activities:	$ 542,280	$ 499,881	$ 448,011
Capital expenditures	(576,065)	(568,230)	(341,382)
Net proceeds from sale or disposition of property and other	29,812	26,100	126,588
Investments	(2,011)	(2,321)	(1,608)
Net cash used in investing activities	(603,861)	(710,907)	(214,168)
Issuance of long-term debt	599,455	566,829	140,812
Repayment of long-term debt	(468,917)	(174,520)	(217,394)
Payments of stock issuance costs	0	(10)	0
Proceeds from issuance of common stock	106,848	0	0
Dividends paid	(160,256)	(154,573)	(150,727)
Redemption of preferred stock	0	0	(15,600)
Repurchase of common stock	0	(5,020)	(1,684)
Tax withholding on stock-based compensation	(3,015)	(2,330)	(757)
Net cash used in financing activities	74,092	230,376	(245,350)
Increase (decrease) in cash and cash equivalents	12,511	19,349	(11,508)
Cash and cash equivalents - beginning of year	53,948	34,599	46,107
Cash and cash equivalents - end of year	66,459	53,948	34,599
MDU Resources Group, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Operating activities:	168,520	294,379	284,075
Capital expenditures	0	(242,692)	(146,370)
Net proceeds from sale or disposition of property and other	0	5,032	(5,665)
Investments in and advances to subsidiaries	(120,000)	(40,000)	(40,000)
Advances from subsidiaries	17,000	70,000	40,000
Investments	(236)	(528)	(468)
Net cash used in investing activities	(103,236)	(208,188)	(152,503)
Issuance of long-term debt	0	199,422	70,080
Repayment of long-term debt	0	(125,961)	(37,569)
Payments of stock issuance costs	0	(10)	0
Proceeds from issuance of common stock	106,848	0	0
Dividends paid	(160,256)	(154,573)	(150,727)
Redemption of preferred stock			(15,600)
Repurchase of common stock	0	(1,920)	(564)
Tax withholding on stock-based compensation	(1,821)	(1,721)	(508)
Net cash used in financing activities	(55,229)	(84,763)	(134,888)
Increase (decrease) in cash and cash equivalents	10,055	1,428	(3,316)
Cash and cash equivalents - beginning of year	2,271	843	4,159
Cash and cash equivalents - end of year	$ 12,326	$ 2,271	$ 843