Condensed Statements of Cash Flows (Details 4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 462,209	$ 661,832	$ 587,062
Capital expenditures	(388,183)	(536,832)	(429,336)
Net proceeds from sale or disposition of property and other	44,826	54,569	28,899
Investments	(1,396)	1,515	(1,041)
Net cash used in investing activities	(305,095)	(382,453)	(904,190)
Issuance of long-term debt	309,064	345,920	606,168
Repayment of long-term debt	(315,647)	(566,498)	(365,247)
Proceeds from issuance of common stock	0	21,898	150,060
Dividends paid	(147,156)	(142,835)	(136,712)
Excess tax benefit on stock-based compensation	0	0	4,729
Tax withholding on stock-based compensation	(323)	0	(5,564)
Net cash provided by financing activities	(194,914)	(255,730)	325,196
Increase (decrease) in cash and cash equivalents	(37,796)	23,424	7,913
Cash and cash equivalents - beginning of year	83,903	60,479	52,566
Cash and cash equivalents - end of year	46,107	83,903	60,479
MDU Resources Group, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	238,125	255,273	208,208
Capital expenditures	(159,570)	(349,985)	(223,251)
Net proceeds from sale or disposition of property and other	3,784	3,268	1,552
Investments in and advances to subsidiaries	(5,000)	(7,000)	(134,451)
Advances from subsidiaries	15,000	100,000	64,500
Investments	(129)	5	(794)
Net cash used in investing activities	(145,915)	(253,712)	(292,444)
Issuance of long-term debt	106,420	224,185	148,959
Repayment of long-term debt	(50,010)	(108,008)	(76,432)
Proceeds from issuance of common stock	0	21,898	150,060
Dividends paid	(147,156)	(142,835)	(136,712)
Excess tax benefit on stock-based compensation	0	0	3,326
Tax withholding on stock-based compensation	(226)	0	(3,896)
Net cash provided by financing activities	(90,972)	(4,760)	85,305
Increase (decrease) in cash and cash equivalents	1,238	(3,199)	1,069
Cash and cash equivalents - beginning of year	2,921	6,120	5,051
Cash and cash equivalents - end of year	$ 4,159	$ 2,921	$ 6,120