Condensed Balance Sheets (Details 2) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 66,459	$ 53,948	$ 34,599	$ 46,107
Receivables, net	836,605	722,945
Inventories	278,407	287,309
Prepayments and other current assets	115,805	119,500
Total current assets	1,297,701	1,184,132
Investments	148,656	138,620
Property, plant and equipment	7,908,628	7,397,321
Less accumulated depreciation, depletion and amortization	2,991,486	2,818,644	2,691,641
Net property, plant and equipment	4,917,142	4,578,677	4,079,188
Deferred charges and other assets:
Goodwill	681,358	664,922	631,791
Operating lease right-of-use assets	115,323
Other	506,207	408,857
Total deferred charges and other assets	1,319,560	1,086,681
Total assets	7,683,059	6,988,110	6,334,666
Current liabilities:
Long-term debt due within one year	16,540	251,854
Accounts payable	403,391	358,505
Taxes payable	48,970	41,929
Dividends payable	41,580	39,695
Accrued compensation	99,269	69,007
Current operating lease liabilities	31,664
Other accrued liabilities	221,502	221,059
Total current liabilities	866,427	986,050
Long-term debt	2,226,567	1,856,841
Deferred credits and other liabilities:
Deferred income taxes	506,583	430,085
Noncurrent operating lease liabilities	83,742
Other	1,152,494	1,148,359
Total deferred credits and other liabilities	1,742,819	1,578,444
Commitments and contingencies
Commitments and contingencies
Authorized - 500,000,000 shares, $1.00 par value
Shares issued - 200,922,790 at December 31, 2019 and 196,564,907 at December 31, 2018	200,923	196,565
Other paid-in capital	1,355,404	1,248,576
Retained earnings	1,336,647	1,163,602
Accumulated other comprehensive loss	(42,102)	(38,342)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)
Total stockholders' equity	2,847,246	2,566,775
Total liabilities and stockholders' equity	$ 7,683,059	$ 6,988,110
Condensed Balance Sheet (Parenthetical)
Common stock, shares authorized	500,000,000	500,000,000
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares issued	200,922,790	196,564,907
Treasury stock, shares	538,921	538,921
MDU Resources Group, Inc. [Member]
Current assets:
Cash and cash equivalents	$ 12,326	$ 2,271	$ 843	$ 4,159
Receivables, net	4,727	92,724
Accounts receivable from subsidiaries	49,943	36,015
Inventories	0	13,293
Prepayments and other current assets	501	14,488
Total current assets	67,497	158,791
Investments	46,294	76,202
Investment in subsidiaries	2,842,068	1,790,886
Property, plant and equipment	0	2,846,715
Less accumulated depreciation, depletion and amortization	0	836,735
Net property, plant and equipment	0	2,009,980
Deferred charges and other assets:
Goodwill	0	4,812
Operating lease right-of-use assets	153
Other	34,367	180,473
Total deferred charges and other assets	34,520	185,285
Total assets	2,990,379	4,221,144
Current liabilities:
Long-term debt due within one year	0	200,711
Accounts payable	2,981	50,051
Accounts payable to subsidiaries	4,752	12,438
Taxes payable	1,253	24,704
Dividends payable	41,580	39,695
Accrued compensation	8,812	14,346
Current operating lease liabilities	96
Other accrued liabilities	7,690	54,099
Total current liabilities	67,164	396,044
Long-term debt	0	586,012
Deferred credits and other liabilities:
Deferred income taxes	0	165,122
Noncurrent operating lease liabilities	56
Other	75,913	507,191
Total deferred credits and other liabilities	75,969	672,313
Commitments and contingencies
Commitments and contingencies
Authorized - 500,000,000 shares, $1.00 par value
Shares issued - 200,922,790 at December 31, 2019 and 196,564,907 at December 31, 2018	200,923	196,565
Other paid-in capital	1,355,404	1,248,576
Retained earnings	1,336,647	1,163,602
Accumulated other comprehensive loss	(42,102)	(38,342)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)
Total stockholders' equity	2,847,246	2,566,775
Total liabilities and stockholders' equity	$ 2,990,379	$ 4,221,144
Condensed Balance Sheet (Parenthetical)
Common stock, shares authorized	500,000,000	500,000,000
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares issued	200,922,790	196,564,907
Treasury stock, shares	538,921	538,921