Basis of presentation	3 Months Ended
Basis of presentation	Mar. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation	Basis of presentation The accompanying consolidated interim financial statements were prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Interim financial statements do not include all disclosures provided in annual financial statements and, accordingly, these financial statements should be read in conjunction with those appearing in the 2022 Annual Report. The information is unaudited but includes all adjustments that are, in the opinion of management, necessary for a fair presentation of the accompanying consolidated interim financial statements and are of a normal recurring nature. Depreciation, depletion and amortization expense is reported separately on the Consolidated Statements of Income and therefore is excluded from the other line items within operating expenses. As part of the Company's continuous review of its business, the Company announced strategic initiatives in 2022 that are expected to enhance its value. On August 4, 2022, the Company announced that its board of directors approved a plan to pursue the separation of Knife River, the construction materials and contracting segment, from the Company. The separation will result in two independent, publicly traded companies, MDU Resources Group, Inc. and Knife River Holding Company, and is expected to be completed on May 31, 2023, subject to certain conditions, including the SEC declaring the Registration Statement on Form 10 for Knife River Holding Company to be effective. On May 3, 2023, the Company's board of directors approved the separation and the distribution of approximately 90 percent of the issued and outstanding shares of Knife River Holding Company to the Company's stockholders. Stockholders of the Company will receive one share of Knife River Holding Company common stock for every four shares of the Company's common stock held on May 22, 2023, the record date for the distribution. The Company will retain approximately 10 percent of Knife River Holding Company's common stock immediately following the separation with the intent to dispose of such shares within twelve months after the separation. Prior to completing the separation, the Company may adjust the percentage of Knife River Holding Company common stock to be distributed to the Company's stockholders and retained by the Company in response to market and other factors. The separation of Knife River is planned as a tax-free spinoff transaction to the Company’s stockholders for U.S. federal income tax purposes. The Company's financial results for the quarter ended March 31, 2023, include Knife River. Upon completion of the separation, the historical results of Knife River will be presented as discontinued operations in the Company's Consolidated Financial Statements. On November 3, 2022, the Company announced its intention to create two pure-play publicly traded companies, one focused on regulated energy delivery and the other on construction materials, and that, to achieve this future structure, the Company's board of directors authorized management to commence a strategic review process of MDU Construction Services. The strategic review is underway and the Company anticipates completing the strategic review during the second quarter of 2023. Discontinued operations include the supporting activities of Fidelity and are shown in income from discontinued operations on the Consolidated Statements of Income. Unless otherwise indicated, the amounts presented in the accompanying notes to the consolidated financial statements relate to the Company's continuing operations. Management has also evaluated the impact of events occurring after March 31, 2023, up to the date of the issuance of these consolidated interim financial statements on May 4, 2023, that would require recognition or disclosure in the Consolidated Financial Statements.