Notes to Condensed Financial Statements (Details 4) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
MDU Resources Group, Inc. [Member]
Condensed Financial Statements, Captions [Line Items]
Cash dividends paid to parent company by consolidated subsidiaries	$ 228.4	$ 177.1	$ 115.9

This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(b))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration