SEC Info℠  
    Home      Search      My Interests      Help      Sign In      Please Sign In

Mdu Resources Group Inc. – ‘10-K’ for 12/31/21 – ‘XML’

On:  Wednesday, 2/23/22, at 12:06pm ET   ·   For:  12/31/21   ·   Accession #:  67716-22-12   ·   File #:  1-03480

Previous ‘10-K’:  ‘10-K’ on 2/19/21 for 12/31/20   ·   Next:  ‘10-K’ on 2/24/23 for 12/31/22   ·   Latest:  ‘10-K’ on 2/22/24 for 12/31/23   ·   25 References:   

Find Words in Filings emoji
 		  in    Show  and   ↓Hints

  As Of               Filer                 Filing    For·On·As Docs:Size

 2/23/22  Mdu Resources Group Inc.          10-K       12/31/21  161:38M

Annual Report   —   Form 10-K

Filing Table of Contents

Document/Exhibit                   Description                      Pages   Size 

 1: 10-K        Mdu Resources 2021 Form 10-K                        HTML   2.57M 
 2: EX-10.K     Mdu Resources Long-Term Performance Incentive Plan  HTML     71K 
 3: EX-10.M     Mdu Resources Restrictive Stock Unit Award          HTML     59K 
                Agreement                                                        
 4: EX-10.W     Mdu Resources 401 K Retirement Plan Amendment       HTML     46K 
                01-01-22                                                         
 5: EX-21       Mdu Resources Subsidiaries of Mdu Resources         HTML     49K 
 6: EX-23       Mdu Resources Consent of Independent Accounting     HTML     36K 
                Firm                                                             
10: EX-95       Mdu Resources Mine Safety Disclosures               HTML    109K 
 7: EX-31.A     Mdu Resources Certification of Chief Executive      HTML     40K 
                Officer                                                          
 8: EX-31.B     Mdu Resources Certification of Chief Financial      HTML     40K 
                Officer                                                          
 9: EX-32       Mdu Resources Certification of CEO and CFO          HTML     38K 
16: R1          Cover page                                          HTML    101K 
17: R2          Audit Information                                   HTML     42K 
18: R3          Consolidated Statements of Income                   HTML    144K 
19: R4          Consolidated Statements of Comprehensive Income     HTML     96K 
20: R5          Consolidated Balance Sheets                         HTML    206K 
21: R6          Consolidated Statements of Equity                   HTML    112K 
22: R7          Consolidated Statements of Cash Flows               HTML    147K 
23: R8          Basis of Presentation                               HTML     45K 
24: R9          Accounting Policies                                 HTML    147K 
25: R10         Revenue from Contract with Customer                 HTML    215K 
26: R11         Business Combinations                               HTML     45K 
27: R12         Property, Plant, and Equipment                      HTML     85K 
28: R13         Regulatory assets and liabilities                   HTML     90K 
29: R14         Goodwill and other intangible assets                HTML     81K 
30: R15         Fair value measurements                             HTML    100K 
31: R16         Debt                                                HTML     99K 
32: R17         Leases                                              HTML     62K 
33: R18         Asset retirement obligations                        HTML     51K 
34: R19         Equity                                              HTML     53K 
35: R20         Stock-Based Compensation                            HTML     62K 
36: R21         Accumulated other comprehensive loss                HTML     75K 
37: R22         Income Taxes                                        HTML    120K 
38: R23         Cash flow information                               HTML     56K 
39: R24         Business segment data                               HTML    200K 
40: R25         Employee benefit plans                              HTML    392K 
41: R26         Jointly owned facilities                            HTML     66K 
42: R27         Regulatory matters                                  HTML     43K 
43: R28         Commitments and contingencies                       HTML     67K 
44: R29         Schedule I-Condensed Financial Information of       HTML    120K 
                Registrant                                                       
45: R30         Basis of Presentation (Policies)                    HTML     51K 
46: R31         Accounting Policies (Policies)                      HTML    130K 
47: R32         Revenue from Contract with Customer (Policies)      HTML     42K 
48: R33         Accumulated other comprehensive loss (Policies)     HTML     38K 
49: R34         Business segment data (Policies)                    HTML     40K 
50: R35         Commitment and Contingencies (Policies)             HTML     40K 
51: R36         Accounting Policies (Tables)                        HTML    105K 
52: R37         Revenue from contracts with customers (Tables)      HTML    208K 
53: R38         Property, Plant, and Equipment (Tables)             HTML     84K 
54: R39         Regulatory assets and liabilities (Tables)          HTML    135K 
55: R40         Goodwill and other intangible assets (Tables)       HTML     86K 
56: R41         Fair value measurements (Tables)                    HTML     98K 
57: R42         Debt (Tables)                                       HTML     91K 
58: R43         Leases (Tables)                                     HTML     60K 
59: R44         Asset Retirement Obligations (Tables)               HTML     49K 
60: R45         Equity (Tables)                                     HTML     48K 
61: R46         Stock-Based Compensation (Tables)                   HTML     62K 
62: R47         Accumulated other comprehensive loss (Tables)       HTML     76K 
63: R48         Income Taxes (Tables)                               HTML    125K 
64: R49         Cash flow information (Tables)                      HTML     56K 
65: R50         Business segment data (Tables)                      HTML    192K 
66: R51         Employee Benefit Plans (Tables)                     HTML    388K 
67: R52         Jointly owned facilities (Tables)                   HTML     66K 
68: R53         Commitment and Contingencies Disclosure (Tables)    HTML     45K 
69: R54         Accounting Policies - Receivables Past Due 90 Days  HTML     39K 
                (Details 1)                                                      
70: R55         Accounting Policies - CECL Table (Details 2)        HTML     67K 
71: R56         Accounting Policies - Accrued Unbilled Revenue      HTML     38K 
                (Details 3)                                                      
72: R57         Accounting Policies - Retainage (Details 4)         HTML     45K 
73: R58         Accounting Policies - Inventory (Details 5)         HTML     54K 
74: R59         Accounting Policies - PPE (Details 6)               HTML     42K 
75: R60         Accounting Policies - Impairment of Long-Lived      HTML     39K 
                Assets (Details 7)                                               
76: R61         Natural Gas Costs Recoverable or Refundable         HTML     41K 
                through Rate Adjustments (Details 8)                             
77: R62         Accounting Policies - Goodwill (Details 9)          HTML     39K 
78: R63         Accounting Policies - Joint Ventures (Details 10)   HTML     70K 
79: R64         Accounting Policies - Derivatives (Details 11)      HTML     41K 
80: R65         Accounting Policies - EPS (Details 12)              HTML     46K 
81: R66         Accounting Policies - Income Taxes (Details 13)     HTML     38K 
82: R67         Disaggregation of revenue (Details)                 HTML    141K 
83: R68         Contract balances (Details 2)                       HTML     59K 
84: R69         Revenue from contracts with customers Remaining     HTML     49K 
                performance obligations (Details 3)                              
85: R70         Business Combinations (Details)                     HTML     65K 
86: R71         Business Combinations - Assets Acquired &           HTML     68K 
                Liabilities Assumed (Details 2)                                  
87: R72         Property, Plant, and Equipment (Details)            HTML    121K 
88: R73         Regulatory assets (Details)                         HTML     87K 
89: R74         Regulatory liabilities (Details 2)                  HTML     68K 
90: R75         Goodwill rollforward (Details)                      HTML     54K 
91: R76         Other intangible assets (Details 2)                 HTML     55K 
92: R77         Future amortization expense (Details 3)             HTML     50K 
93: R78         Fair value measurements insurance contracts         HTML     42K 
                (Details)                                                        
94: R79         Available-for-sale securities (Details 2)           HTML     53K 
95: R80         Fair value measurements (Details 3)                 HTML     69K 
96: R81         Fair value measurements (Details 5)                 HTML     47K 
97: R82         Credit facilities (Details)                         HTML     66K 
98: R83         Short-term Debt (Details 2)                         HTML     45K 
99: R84         Long-term debt outstanding (Details 3)              HTML     68K 
100: R85         Long-term borrowings (Details 4)                    HTML     82K  
101: R86         Schedule of debt maturities (Details 5)             HTML     54K  
102: R87         Lease costs (Details)                               HTML     53K  
103: R88         Operating lease liabilities undiscounted cash       HTML     56K  
                flows maturity schedule (Details 2)                              
104: R89         Lessor accounting (Details 3)                       HTML     41K  
105: R90         Asset Retirement Obligations (Details)              HTML     54K  
106: R91         Common stock (Details)                              HTML     49K  
107: R92         Common stock Common stock issuance (Details 2)      HTML     53K  
108: R93         Preferred Stock (Details 3)                         HTML     44K  
109: R94         Stock based compensation plans (Details)            HTML     46K  
110: R95         Stock awards (Details 2)                            HTML     42K  
111: R96         Restricted stock awards (Details 3)                 HTML     43K  
112: R97         Performance share awards (Details 4)                HTML    105K  
113: R98         Accumulated other comprehensive loss (Details)      HTML     70K  
114: R99         Reclassification out of accumulated other           HTML     72K  
                comprehensive loss (Details 2)                                   
115: R100        Components of income before income taxes from       HTML     47K  
                continuing operations (Details)                                  
116: R101        Income tax expense (Benefit) (Details 2)            HTML     64K  
117: R102        Components of deferred tax assets and liabilities   HTML     76K  
                (Details 3)                                                      
118: R103        Carryforwards (Details 4)                           HTML     46K  
119: R104        Deferred tax reconciliation (Details 5)             HTML     48K  
120: R105        Income tax expense (Benefit) Statutory Rate Versus  HTML     74K  
                Actual Rate (Details 6)                                          
121: R106        Cash flow information (Details)                     HTML     54K  
122: R107        Business segment data (Details)                     HTML    172K  
123: R108        Change in benefit obligations and plan assets       HTML    124K  
                (Details)                                                        
124: R109        Benefit obligations in excess of plan assets        HTML     49K  
                (Details 2)                                                      
125: R110        Components of net periodic benefit cost (Details    HTML     99K  
                3)                                                               
126: R111        Weighted average assumptions (Details 4)            HTML     61K  
127: R112        Investment Allocations (Details 5)                  HTML     55K  
128: R113        Health care rate assumptions and cost trend rate    HTML     47K  
                (Details 6)                                                      
129: R114        Estimated future benefit payments and subsidies     HTML     78K  
                (Details 7)                                                      
130: R115        Fair value - pension (Details 8)                    HTML     99K  
131: R116        Fair value - other postretirement (Details 9)       HTML     94K  
132: R117        Nonqualified Benefit Plans Benefit Obligations      HTML     46K  
                (Details 10)                                                     
133: R118        Nonqualified Benefit Plans Components of NPBC       HTML     53K  
                (Details 11)                                                     
134: R119        Nonqualified Benefit Plans Weighted Average         HTML     45K  
                Assumptions (Details 12)                                         
135: R120        Nonqualified Benefit Plans Future Benefit Payments  HTML     53K  
                (Details 13)                                                     
136: R121        Nonqualified Benefit Plans Contributions (Details   HTML     42K  
                14)                                                              
137: R122        Nonqualified Benefit Plans Investments (Details     HTML     48K  
                15)                                                              
138: R123        Defined Contribution Benefit Plans Contribution     HTML     40K  
                (Details 16)                                                     
139: R124        Multiemployer Plans Zones (Details 17)              HTML     47K  
140: R125        Multiemployer Plans Participation by Plan (Details  HTML    130K  
                18)                                                              
141: R126        Multiemployer Plan Contributions (Details 19)       HTML     44K  
142: R127        Jointly owned facilities (Details)                  HTML     62K  
143: R128        Mnpuc (Details)                                     HTML     43K  
144: R129        Ndpsc (Details 2)                                   HTML     45K  
145: R130        Sdpuc (Details 3)                                   HTML     42K  
146: R131        Wutc (Details 4)                                    HTML     45K  
147: R132        Ferc (Details 5)                                    HTML     43K  
148: R133        Litigation (Details)                                HTML     42K  
149: R134        Enviromental matters (Details 2)                    HTML     70K  
150: R135        Purchase commitments (Details 3)                    HTML     57K  
151: R136        Guarantees (Details 4)                              HTML     62K  
152: R137        Variable interest entities (Details 5)              HTML     40K  
153: R138        Condensed Statements of Income and Comprehensive    HTML     57K  
                Income (Details)                                                 
154: R139        Condensed Balance Sheets (Details 2)                HTML    183K  
155: R140        Condensed Statements of Cash Flows (Details 3)      HTML     79K  
156: R141        Notes to Condensed Financial Statements (Details    HTML     40K  
                4)                                                               
159: XML         IDEA XML File -- Filing Summary                      XML    292K  
157: XML         XBRL Instance -- mdu-20211231_htm                    XML   6.68M  
158: EXCEL       IDEA Workbook of Financial Reports                  XLSX    226K  
12: EX-101.CAL  XBRL Calculations -- mdu-20211231_cal                XML    247K 
13: EX-101.DEF  XBRL Definitions -- mdu-20211231_def                 XML   1.91M 
14: EX-101.LAB  XBRL Labels -- mdu-20211231_lab                      XML   3.18M 
15: EX-101.PRE  XBRL Presentations -- mdu-20211231_pre               XML   2.26M 
11: EX-101.SCH  XBRL Schema -- mdu-20211231                          XSD    332K 
160: JSON        XBRL Instance as JSON Data -- MetaLinks              750±  1.05M  
161: ZIP         XBRL Zipped Folder -- 0000067716-22-000012-xbrl      Zip   6.22M

‘XML’   —   IDEA XML File — Filing Summary

This Document is an IDEA XML File.

                                                                                                                                                                                
<?xml version="1.0" encoding="windows-1252"?>
<FilingSummary>
<Version> 3.22.0.1 </Version>
<ProcessingTime/>
<ReportFormat> html </ReportFormat>
<ContextCount> 838 </ContextCount>
<ElementCount> 710 </ElementCount>
<EntityCount> 1 </EntityCount>
<FootnotesReported> false </FootnotesReported>
<SegmentCount> 185 </SegmentCount>
<ScenarioCount> 0 </ScenarioCount>
<TuplesReported> false </TuplesReported>
<UnitCount> 5 </UnitCount>
<MyReports>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R1.htm </HtmlFileName>
<LongName> 000010001 - Document - Cover page </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Coverpage </Role>
<ShortName> Cover page </ShortName>
<MenuCategory> Cover </MenuCategory>
<Position> 1 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R2.htm </HtmlFileName>
<LongName> 000020002 - Document - Audit Information </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AuditInformation </Role>
<ShortName> Audit Information </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 2 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R3.htm </HtmlFileName>
<LongName> 100010003 - Statement - Consolidated Statements of Income </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ConsolidatedStatementsofIncome </Role>
<ShortName> Consolidated Statements of Income </ShortName>
<MenuCategory> Uncategorized </MenuCategory>
<Position> 3 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R4.htm </HtmlFileName>
<LongName> 100020004 - Statement - Consolidated Statements of Comprehensive Income </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ConsolidatedStatementsofComprehensiveIncome </Role>
<ShortName> Consolidated Statements of Comprehensive Income </ShortName>
<MenuCategory> Statements </MenuCategory>
<Position> 4 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R5.htm </HtmlFileName>
<LongName> 100030005 - Statement - Consolidated Balance Sheets </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ConsolidatedBalanceSheets </Role>
<ShortName> Consolidated Balance Sheets </ShortName>
<MenuCategory> Statements </MenuCategory>
<Position> 5 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R6.htm </HtmlFileName>
<LongName> 100040006 - Statement - Consolidated Statements of Equity </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ConsolidatedStatementsofEquity </Role>
<ShortName> Consolidated Statements of Equity </ShortName>
<MenuCategory> Statements </MenuCategory>
<Position> 6 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R7.htm </HtmlFileName>
<LongName> 100050007 - Statement - Consolidated Statements of Cash Flows </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ConsolidatedStatementsofCashFlows </Role>
<ShortName> Consolidated Statements of Cash Flows </ShortName>
<MenuCategory> Statements </MenuCategory>
<Position> 7 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R8.htm </HtmlFileName>
<LongName> 210011001 - Disclosure - Basis of Presentation </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/BasisofPresentation </Role>
<ShortName> Basis of Presentation </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 8 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R9.htm </HtmlFileName>
<LongName> 210031002 - Disclosure - Accounting Policies </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPolicies </Role>
<ShortName> Accounting Policies </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 9 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R10.htm </HtmlFileName>
<LongName> 210191003 - Disclosure - Revenue from Contract with Customer </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/RevenuefromContractwithCustomer </Role>
<ShortName> Revenue from Contract with Customer </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 10 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R11.htm </HtmlFileName>
<LongName> 210251004 - Disclosure - Business Combinations </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/BusinessCombinations </Role>
<ShortName> Business Combinations </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 11 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R12.htm </HtmlFileName>
<LongName> 210281005 - Disclosure - Property, Plant, and Equipment </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/PropertyPlantandEquipment </Role>
<ShortName> Property, Plant, and Equipment </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 12 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R13.htm </HtmlFileName>
<LongName> 210311006 - Disclosure - Regulatory assets and liabilities </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Regulatoryassetsandliabilities </Role>
<ShortName> Regulatory assets and liabilities </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 13 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R14.htm </HtmlFileName>
<LongName> 210351007 - Disclosure - Goodwill and other intangible assets </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Goodwillandotherintangibleassets </Role>
<ShortName> Goodwill and other intangible assets </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 14 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R15.htm </HtmlFileName>
<LongName> 210401008 - Disclosure - Fair value measurements </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Fairvaluemeasurements </Role>
<ShortName> Fair value measurements </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 15 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R16.htm </HtmlFileName>
<LongName> 210461009 - Disclosure - Debt </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Debt </Role>
<ShortName> Debt </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 16 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R17.htm </HtmlFileName>
<LongName> 210531010 - Disclosure - Leases </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Leases </Role>
<ShortName> Leases </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 17 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R18.htm </HtmlFileName>
<LongName> 210581011 - Disclosure - Asset retirement obligations </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Assetretirementobligations </Role>
<ShortName> Asset retirement obligations </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 18 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R19.htm </HtmlFileName>
<LongName> 210611012 - Disclosure - Equity </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Equity </Role>
<ShortName> Equity </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 19 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R20.htm </HtmlFileName>
<LongName> 210661013 - Disclosure - Stock-Based Compensation </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/StockBasedCompensation </Role>
<ShortName> Stock-Based Compensation </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 20 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R21.htm </HtmlFileName>
<LongName> 210721014 - Disclosure - Accumulated other comprehensive loss </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Accumulatedothercomprehensiveloss </Role>
<ShortName> Accumulated other comprehensive loss </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 21 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R22.htm </HtmlFileName>
<LongName> 210771015 - Disclosure - Income Taxes </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/IncomeTaxes </Role>
<ShortName> Income Taxes </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 22 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R23.htm </HtmlFileName>
<LongName> 210851016 - Disclosure - Cash flow information </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Cashflowinformation </Role>
<ShortName> Cash flow information </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 23 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R24.htm </HtmlFileName>
<LongName> 210881017 - Disclosure - Business segment data </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Businesssegmentdata </Role>
<ShortName> Business segment data </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 24 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R25.htm </HtmlFileName>
<LongName> 210921018 - Disclosure - Employee benefit plans </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Employeebenefitplans </Role>
<ShortName> Employee benefit plans </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 25 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R26.htm </HtmlFileName>
<LongName> 211131019 - Disclosure - Jointly owned facilities </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Jointlyownedfacilities </Role>
<ShortName> Jointly owned facilities </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 26 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R27.htm </HtmlFileName>
<LongName> 211161020 - Disclosure - Regulatory matters </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Regulatorymatters </Role>
<ShortName> Regulatory matters </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 27 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R28.htm </HtmlFileName>
<LongName> 211221021 - Disclosure - Commitments and contingencies </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/Commitmentsandcontingencies </Role>
<ShortName> Commitments and contingencies </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 28 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R29.htm </HtmlFileName>
<LongName> 211301022 - Disclosure - Schedule I-Condensed Financial Information of Registrant </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ScheduleICondensedFinancialInformationofRegistrant </Role>
<ShortName> Schedule I-Condensed Financial Information of Registrant </ShortName>
<MenuCategory> Notes </MenuCategory>
<Position> 29 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R30.htm </HtmlFileName>
<LongName> 220022001 - Disclosure - Basis of Presentation (Policies) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/BasisofPresentationPolicies </Role>
<ShortName> Basis of Presentation (Policies) </ShortName>
<MenuCategory> Policies </MenuCategory>
<ParentRole> http://www.mdu.com/role/AccountingPolicies </ParentRole>
<Position> 30 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R31.htm </HtmlFileName>
<LongName> 220042002 - Disclosure - Accounting Policies (Policies) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesPolicies </Role>
<ShortName> Accounting Policies (Policies) </ShortName>
<MenuCategory> Policies </MenuCategory>
<ParentRole> http://www.mdu.com/role/AccountingPolicies </ParentRole>
<Position> 31 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R32.htm </HtmlFileName>
<LongName> 220202003 - Disclosure - Revenue from Contract with Customer (Policies) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/RevenuefromContractwithCustomerPolicies </Role>
<ShortName> Revenue from Contract with Customer (Policies) </ShortName>
<MenuCategory> Policies </MenuCategory>
<ParentRole> http://www.mdu.com/role/AccountingPolicies </ParentRole>
<Position> 32 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R33.htm </HtmlFileName>
<LongName> 220732004 - Disclosure - Accumulated other comprehensive loss (Policies) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccumulatedothercomprehensivelossPolicies </Role>
<ShortName> Accumulated other comprehensive loss (Policies) </ShortName>
<MenuCategory> Policies </MenuCategory>
<ParentRole> http://www.mdu.com/role/AccountingPolicies </ParentRole>
<Position> 33 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R34.htm </HtmlFileName>
<LongName> 220892005 - Disclosure - Business segment data (Policies) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/BusinesssegmentdataPolicies </Role>
<ShortName> Business segment data (Policies) </ShortName>
<MenuCategory> Policies </MenuCategory>
<ParentRole> http://www.mdu.com/role/AccountingPolicies </ParentRole>
<Position> 34 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R35.htm </HtmlFileName>
<LongName> 221232006 - Disclosure - Commitment and Contingencies (Policies) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CommitmentandContingenciesPolicies </Role>
<ShortName> Commitment and Contingencies (Policies) </ShortName>
<MenuCategory> Policies </MenuCategory>
<ParentRole> http://www.mdu.com/role/AccountingPolicies </ParentRole>
<Position> 35 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R36.htm </HtmlFileName>
<LongName> 230053001 - Disclosure - Accounting Policies (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesTables </Role>
<ShortName> Accounting Policies (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/AccountingPolicies </ParentRole>
<Position> 36 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R37.htm </HtmlFileName>
<LongName> 230213002 - Disclosure - Revenue from contracts with customers (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/RevenuefromcontractswithcustomersTables </Role>
<ShortName> Revenue from contracts with customers (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<Position> 37 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R38.htm </HtmlFileName>
<LongName> 230293003 - Disclosure - Property, Plant, and Equipment (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/PropertyPlantandEquipmentTables </Role>
<ShortName> Property, Plant, and Equipment (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/PropertyPlantandEquipment </ParentRole>
<Position> 38 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R39.htm </HtmlFileName>
<LongName> 230323004 - Disclosure - Regulatory assets and liabilities (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/RegulatoryassetsandliabilitiesTables </Role>
<ShortName> Regulatory assets and liabilities (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/Regulatoryassetsandliabilities </ParentRole>
<Position> 39 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R40.htm </HtmlFileName>
<LongName> 230363005 - Disclosure - Goodwill and other intangible assets (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/GoodwillandotherintangibleassetsTables </Role>
<ShortName> Goodwill and other intangible assets (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/Goodwillandotherintangibleassets </ParentRole>
<Position> 40 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R41.htm </HtmlFileName>
<LongName> 230413006 - Disclosure - Fair value measurements (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/FairvaluemeasurementsTables </Role>
<ShortName> Fair value measurements (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/Fairvaluemeasurements </ParentRole>
<Position> 41 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R42.htm </HtmlFileName>
<LongName> 230473007 - Disclosure - Debt (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/DebtTables </Role>
<ShortName> Debt (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/Debt </ParentRole>
<Position> 42 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R43.htm </HtmlFileName>
<LongName> 230543008 - Disclosure - Leases (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/LeasesTables </Role>
<ShortName> Leases (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/Leases </ParentRole>
<Position> 43 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R44.htm </HtmlFileName>
<LongName> 230593009 - Disclosure - Asset Retirement Obligations (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AssetRetirementObligationsTables </Role>
<ShortName> Asset Retirement Obligations (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<Position> 44 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R45.htm </HtmlFileName>
<LongName> 230623010 - Disclosure - Equity (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/EquityTables </Role>
<ShortName> Equity (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/Equity </ParentRole>
<Position> 45 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R46.htm </HtmlFileName>
<LongName> 230673011 - Disclosure - Stock-Based Compensation (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/StockBasedCompensationTables </Role>
<ShortName> Stock-Based Compensation (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/StockBasedCompensation </ParentRole>
<Position> 46 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R47.htm </HtmlFileName>
<LongName> 230743012 - Disclosure - Accumulated other comprehensive loss (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccumulatedothercomprehensivelossTables </Role>
<ShortName> Accumulated other comprehensive loss (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/Accumulatedothercomprehensiveloss </ParentRole>
<Position> 47 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R48.htm </HtmlFileName>
<LongName> 230783013 - Disclosure - Income Taxes (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/IncomeTaxesTables </Role>
<ShortName> Income Taxes (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/IncomeTaxes </ParentRole>
<Position> 48 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R49.htm </HtmlFileName>
<LongName> 230863014 - Disclosure - Cash flow information (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CashflowinformationTables </Role>
<ShortName> Cash flow information (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/Cashflowinformation </ParentRole>
<Position> 49 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R50.htm </HtmlFileName>
<LongName> 230903015 - Disclosure - Business segment data (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/BusinesssegmentdataTables </Role>
<ShortName> Business segment data (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/Businesssegmentdata </ParentRole>
<Position> 50 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R51.htm </HtmlFileName>
<LongName> 230933016 - Disclosure - Employee Benefit Plans (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/EmployeeBenefitPlansTables </Role>
<ShortName> Employee Benefit Plans (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<Position> 51 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R52.htm </HtmlFileName>
<LongName> 231143017 - Disclosure - Jointly owned facilities (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/JointlyownedfacilitiesTables </Role>
<ShortName> Jointly owned facilities (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<ParentRole> http://www.mdu.com/role/Jointlyownedfacilities </ParentRole>
<Position> 52 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R53.htm </HtmlFileName>
<LongName> 231243018 - Disclosure - Commitment and Contingencies Disclosure (Tables) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CommitmentandContingenciesDisclosureTables </Role>
<ShortName> Commitment and Contingencies Disclosure (Tables) </ShortName>
<MenuCategory> Tables </MenuCategory>
<Position> 53 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R54.htm </HtmlFileName>
<LongName> 240064001 - Disclosure - Accounting Policies - Receivables Past Due 90 Days (Details 1) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesReceivablesPastDue90DaysDetails1 </Role>
<ShortName> Accounting Policies - Receivables Past Due 90 Days (Details 1) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 54 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R55.htm </HtmlFileName>
<LongName> 240074002 - Disclosure - Accounting Policies - CECL Table (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesCECLTableDetails2 </Role>
<ShortName> Accounting Policies - CECL Table (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 55 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R56.htm </HtmlFileName>
<LongName> 240084003 - Disclosure - Accounting Policies - Accrued Unbilled Revenue (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesAccruedUnbilledRevenueDetails3 </Role>
<ShortName> Accounting Policies - Accrued Unbilled Revenue (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 56 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R57.htm </HtmlFileName>
<LongName> 240094004 - Disclosure - Accounting Policies - Retainage (Details 4) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesRetainageDetails4 </Role>
<ShortName> Accounting Policies - Retainage (Details 4) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 57 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R58.htm </HtmlFileName>
<LongName> 240104005 - Disclosure - Accounting Policies - Inventory (Details 5) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesInventoryDetails5 </Role>
<ShortName> Accounting Policies - Inventory (Details 5) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 58 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R59.htm </HtmlFileName>
<LongName> 240114006 - Disclosure - Accounting Policies - PPE (Details 6) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesPPEDetails6 </Role>
<ShortName> Accounting Policies - PPE (Details 6) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 59 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R60.htm </HtmlFileName>
<LongName> 240124007 - Disclosure - Accounting Policies - Impairment of Long-Lived Assets (Details 7) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesImpairmentofLongLivedAssetsDetails7 </Role>
<ShortName> Accounting Policies - Impairment of Long-Lived Assets (Details 7) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 60 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R61.htm </HtmlFileName>
<LongName> 240134008 - Disclosure - Natural Gas Costs Recoverable or Refundable through Rate Adjustments (Details 8) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/NaturalGasCostsRecoverableorRefundablethroughRateAdjustmentsDetails8 </Role>
<ShortName> Natural Gas Costs Recoverable or Refundable through Rate Adjustments (Details 8) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 61 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R62.htm </HtmlFileName>
<LongName> 240144009 - Disclosure - Accounting Policies - Goodwill (Details 9) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesGoodwillDetails9 </Role>
<ShortName> Accounting Policies - Goodwill (Details 9) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 62 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R63.htm </HtmlFileName>
<LongName> 240154010 - Disclosure - Accounting Policies - Joint Ventures (Details 10) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesJointVenturesDetails10 </Role>
<ShortName> Accounting Policies - Joint Ventures (Details 10) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 63 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R64.htm </HtmlFileName>
<LongName> 240164011 - Disclosure - Accounting Policies - Derivatives (Details 11) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesDerivativesDetails11 </Role>
<ShortName> Accounting Policies - Derivatives (Details 11) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 64 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R65.htm </HtmlFileName>
<LongName> 240174012 - Disclosure - Accounting Policies - EPS (Details 12) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesEPSDetails12 </Role>
<ShortName> Accounting Policies - EPS (Details 12) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 65 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R66.htm </HtmlFileName>
<LongName> 240184013 - Disclosure - Accounting Policies - Income Taxes (Details 13) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccountingPoliciesIncomeTaxesDetails13 </Role>
<ShortName> Accounting Policies - Income Taxes (Details 13) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 66 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R67.htm </HtmlFileName>
<LongName> 240224014 - Disclosure - Disaggregation of revenue (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/DisaggregationofrevenueDetails </Role>
<ShortName> Disaggregation of revenue (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 67 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R68.htm </HtmlFileName>
<LongName> 240234015 - Disclosure - Contract balances (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ContractbalancesDetails2 </Role>
<ShortName> Contract balances (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 68 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R69.htm </HtmlFileName>
<LongName> 240244016 - Disclosure - Revenue from contracts with customers Remaining performance obligations (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/RevenuefromcontractswithcustomersRemainingperformanceobligationsDetails3 </Role>
<ShortName> Revenue from contracts with customers Remaining performance obligations (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 69 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R70.htm </HtmlFileName>
<LongName> 240264017 - Disclosure - Business Combinations (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/BusinessCombinationsDetails </Role>
<ShortName> Business Combinations (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<ParentRole> http://www.mdu.com/role/BusinessCombinations </ParentRole>
<Position> 70 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R71.htm </HtmlFileName>
<LongName> 240274018 - Disclosure - Business Combinations - Assets Acquired & Liabilities Assumed (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/BusinessCombinationsAssetsAcquiredLiabilitiesAssumedDetails2 </Role>
<ShortName> Business Combinations - Assets Acquired & Liabilities Assumed (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 71 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R72.htm </HtmlFileName>
<LongName> 240304019 - Disclosure - Property, Plant, and Equipment (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/PropertyPlantandEquipmentDetails </Role>
<ShortName> Property, Plant, and Equipment (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<ParentRole> http://www.mdu.com/role/PropertyPlantandEquipmentTables </ParentRole>
<Position> 72 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R73.htm </HtmlFileName>
<LongName> 240334020 - Disclosure - Regulatory assets (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/RegulatoryassetsDetails </Role>
<ShortName> Regulatory assets (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<ParentRole> http://www.mdu.com/role/RegulatoryassetsandliabilitiesTables </ParentRole>
<Position> 73 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R74.htm </HtmlFileName>
<LongName> 240344021 - Disclosure - Regulatory liabilities (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/RegulatoryliabilitiesDetails2 </Role>
<ShortName> Regulatory liabilities (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 74 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R75.htm </HtmlFileName>
<LongName> 240374022 - Disclosure - Goodwill rollforward (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/GoodwillrollforwardDetails </Role>
<ShortName> Goodwill rollforward (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 75 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R76.htm </HtmlFileName>
<LongName> 240384023 - Disclosure - Other intangible assets (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/OtherintangibleassetsDetails2 </Role>
<ShortName> Other intangible assets (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 76 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R77.htm </HtmlFileName>
<LongName> 240394024 - Disclosure - Future amortization expense (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/FutureamortizationexpenseDetails3 </Role>
<ShortName> Future amortization expense (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 77 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R78.htm </HtmlFileName>
<LongName> 240424025 - Disclosure - Fair value measurements insurance contracts (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/FairvaluemeasurementsinsurancecontractsDetails </Role>
<ShortName> Fair value measurements insurance contracts (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 78 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R79.htm </HtmlFileName>
<LongName> 240434026 - Disclosure - Available-for-sale securities (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AvailableforsalesecuritiesDetails2 </Role>
<ShortName> Available-for-sale securities (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 79 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R80.htm </HtmlFileName>
<LongName> 240444027 - Disclosure - Fair value measurements (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/FairvaluemeasurementsDetails3 </Role>
<ShortName> Fair value measurements (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<ParentRole> http://www.mdu.com/role/FairvaluemeasurementsTables </ParentRole>
<Position> 80 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R81.htm </HtmlFileName>
<LongName> 240454028 - Disclosure - Fair value measurements (Details 5) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/FairvaluemeasurementsDetails5 </Role>
<ShortName> Fair value measurements (Details 5) </ShortName>
<MenuCategory> Details </MenuCategory>
<ParentRole> http://www.mdu.com/role/FairvaluemeasurementsTables </ParentRole>
<Position> 81 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R82.htm </HtmlFileName>
<LongName> 240484029 - Disclosure - Credit facilities (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CreditfacilitiesDetails </Role>
<ShortName> Credit facilities (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 82 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R83.htm </HtmlFileName>
<LongName> 240494030 - Disclosure - Short-term Debt (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ShorttermDebtDetails2 </Role>
<ShortName> Short-term Debt (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 83 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R84.htm </HtmlFileName>
<LongName> 240504031 - Disclosure - Long-term debt outstanding (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/LongtermdebtoutstandingDetails3 </Role>
<ShortName> Long-term debt outstanding (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 84 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R85.htm </HtmlFileName>
<LongName> 240514032 - Disclosure - Long-term borrowings (Details 4) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/LongtermborrowingsDetails4 </Role>
<ShortName> Long-term borrowings (Details 4) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 85 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R86.htm </HtmlFileName>
<LongName> 240524033 - Disclosure - Schedule of debt maturities (Details 5) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ScheduleofdebtmaturitiesDetails5 </Role>
<ShortName> Schedule of debt maturities (Details 5) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 86 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R87.htm </HtmlFileName>
<LongName> 240554034 - Disclosure - Lease costs (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/LeasecostsDetails </Role>
<ShortName> Lease costs (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 87 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R88.htm </HtmlFileName>
<LongName> 240564035 - Disclosure - Operating lease liabilities undiscounted cash flows maturity schedule (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/OperatingleaseliabilitiesundiscountedcashflowsmaturityscheduleDetails2 </Role>
<ShortName> Operating lease liabilities undiscounted cash flows maturity schedule (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 88 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R89.htm </HtmlFileName>
<LongName> 240574036 - Disclosure - Lessor accounting (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/LessoraccountingDetails3 </Role>
<ShortName> Lessor accounting (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 89 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R90.htm </HtmlFileName>
<LongName> 240604037 - Disclosure - Asset Retirement Obligations (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AssetRetirementObligationsDetails </Role>
<ShortName> Asset Retirement Obligations (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<ParentRole> http://www.mdu.com/role/AssetRetirementObligationsTables </ParentRole>
<Position> 90 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R91.htm </HtmlFileName>
<LongName> 240634038 - Disclosure - Common stock (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CommonstockDetails </Role>
<ShortName> Common stock (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 91 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R92.htm </HtmlFileName>
<LongName> 240644039 - Disclosure - Common stock Common stock issuance (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CommonstockCommonstockissuanceDetails2 </Role>
<ShortName> Common stock Common stock issuance (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 92 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R93.htm </HtmlFileName>
<LongName> 240654040 - Disclosure - Preferred Stock (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/PreferredStockDetails3 </Role>
<ShortName> Preferred Stock (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 93 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R94.htm </HtmlFileName>
<LongName> 240684041 - Disclosure - Stock based compensation plans (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/StockbasedcompensationplansDetails </Role>
<ShortName> Stock based compensation plans (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 94 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R95.htm </HtmlFileName>
<LongName> 240694042 - Disclosure - Stock awards (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/StockawardsDetails2 </Role>
<ShortName> Stock awards (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 95 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R96.htm </HtmlFileName>
<LongName> 240704043 - Disclosure - Restricted stock awards (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/RestrictedstockawardsDetails3 </Role>
<ShortName> Restricted stock awards (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 96 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R97.htm </HtmlFileName>
<LongName> 240714044 - Disclosure - Performance share awards (Details 4) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/PerformanceshareawardsDetails4 </Role>
<ShortName> Performance share awards (Details 4) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 97 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R98.htm </HtmlFileName>
<LongName> 240754045 - Disclosure - Accumulated other comprehensive loss (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/AccumulatedothercomprehensivelossDetails </Role>
<ShortName> Accumulated other comprehensive loss (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<ParentRole> http://www.mdu.com/role/AccumulatedothercomprehensivelossTables </ParentRole>
<Position> 98 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R99.htm </HtmlFileName>
<LongName> 240764046 - Disclosure - Reclassification out of accumulated other comprehensive loss (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ReclassificationoutofaccumulatedothercomprehensivelossDetails2 </Role>
<ShortName> Reclassification out of accumulated other comprehensive loss (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 99 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R100.htm </HtmlFileName>
<LongName> 240794047 - Disclosure - Components of income before income taxes from continuing operations (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ComponentsofincomebeforeincometaxesfromcontinuingoperationsDetails </Role>
<ShortName> Components of income before income taxes from continuing operations (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 100 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R101.htm </HtmlFileName>
<LongName> 240804048 - Disclosure - Income tax expense (benefit) (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/IncometaxexpensebenefitDetails2 </Role>
<ShortName> Income tax expense (benefit) (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 101 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R102.htm </HtmlFileName>
<LongName> 240814049 - Disclosure - Components of deferred tax assets and liabilities (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ComponentsofdeferredtaxassetsandliabilitiesDetails3 </Role>
<ShortName> Components of deferred tax assets and liabilities (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 102 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R103.htm </HtmlFileName>
<LongName> 240824050 - Disclosure - Carryforwards (Details 4) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CarryforwardsDetails4 </Role>
<ShortName> Carryforwards (Details 4) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 103 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R104.htm </HtmlFileName>
<LongName> 240834051 - Disclosure - Deferred tax reconciliation (Details 5) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/DeferredtaxreconciliationDetails5 </Role>
<ShortName> Deferred tax reconciliation (Details 5) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 104 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R105.htm </HtmlFileName>
<LongName> 240844052 - Disclosure - Income tax expense (benefit) statutory rate versus actual rate (Details 6) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/IncometaxexpensebenefitstatutoryrateversusactualrateDetails6 </Role>
<ShortName> Income tax expense (benefit) statutory rate versus actual rate (Details 6) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 105 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R106.htm </HtmlFileName>
<LongName> 240874053 - Disclosure - Cash flow information (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CashflowinformationDetails </Role>
<ShortName> Cash flow information (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<ParentRole> http://www.mdu.com/role/CashflowinformationTables </ParentRole>
<Position> 106 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R107.htm </HtmlFileName>
<LongName> 240914054 - Disclosure - Business segment data (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/BusinesssegmentdataDetails </Role>
<ShortName> Business segment data (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<ParentRole> http://www.mdu.com/role/BusinesssegmentdataTables </ParentRole>
<Position> 107 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R108.htm </HtmlFileName>
<LongName> 240944055 - Disclosure - Change in benefit obligations and plan assets (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ChangeinbenefitobligationsandplanassetsDetails </Role>
<ShortName> Change in benefit obligations and plan assets (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 108 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R109.htm </HtmlFileName>
<LongName> 240954056 - Disclosure - Benefit obligations in excess of plan assets (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/BenefitobligationsinexcessofplanassetsDetails2 </Role>
<ShortName> Benefit obligations in excess of plan assets (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 109 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R110.htm </HtmlFileName>
<LongName> 240964057 - Disclosure - Components of net periodic benefit cost (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/ComponentsofnetperiodicbenefitcostDetails3 </Role>
<ShortName> Components of net periodic benefit cost (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 110 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R111.htm </HtmlFileName>
<LongName> 240974058 - Disclosure - Weighted average assumptions (Details 4) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/WeightedaverageassumptionsDetails4 </Role>
<ShortName> Weighted average assumptions (Details 4) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 111 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R112.htm </HtmlFileName>
<LongName> 240984059 - Disclosure - Investment Allocations (Details 5) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/InvestmentAllocationsDetails5 </Role>
<ShortName> Investment Allocations (Details 5) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 112 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R113.htm </HtmlFileName>
<LongName> 240994060 - Disclosure - Health care rate assumptions and cost trend rate (Details 6) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/HealthcarerateassumptionsandcosttrendrateDetails6 </Role>
<ShortName> Health care rate assumptions and cost trend rate (Details 6) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 113 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R114.htm </HtmlFileName>
<LongName> 241004061 - Disclosure - Estimated future benefit payments and subsidies (Details 7) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/EstimatedfuturebenefitpaymentsandsubsidiesDetails7 </Role>
<ShortName> Estimated future benefit payments and subsidies (Details 7) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 114 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R115.htm </HtmlFileName>
<LongName> 241014062 - Disclosure - Fair value - pension (Details 8) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/FairvaluepensionDetails8 </Role>
<ShortName> Fair value - pension (Details 8) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 115 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R116.htm </HtmlFileName>
<LongName> 241024063 - Disclosure - Fair value - other postretirement (Details 9) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/FairvalueotherpostretirementDetails9 </Role>
<ShortName> Fair value - other postretirement (Details 9) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 116 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R117.htm </HtmlFileName>
<LongName> 241034064 - Disclosure - Nonqualified Benefit Plans Benefit Obligations (Details 10) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/NonqualifiedBenefitPlansBenefitObligationsDetails10 </Role>
<ShortName> Nonqualified Benefit Plans Benefit Obligations (Details 10) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 117 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R118.htm </HtmlFileName>
<LongName> 241044065 - Disclosure - Nonqualified Benefit Plans Components of NPBC (Details 11) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/NonqualifiedBenefitPlansComponentsofNPBCDetails11 </Role>
<ShortName> Nonqualified Benefit Plans Components of NPBC (Details 11) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 118 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R119.htm </HtmlFileName>
<LongName> 241054066 - Disclosure - Nonqualified Benefit Plans Weighted Average Assumptions (Details 12) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/NonqualifiedBenefitPlansWeightedAverageAssumptionsDetails12 </Role>
<ShortName> Nonqualified Benefit Plans Weighted Average Assumptions (Details 12) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 119 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R120.htm </HtmlFileName>
<LongName> 241064067 - Disclosure - Nonqualified Benefit Plans Future Benefit Payments (Details 13) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/NonqualifiedBenefitPlansFutureBenefitPaymentsDetails13 </Role>
<ShortName> Nonqualified Benefit Plans Future Benefit Payments (Details 13) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 120 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R121.htm </HtmlFileName>
<LongName> 241074068 - Disclosure - Nonqualified Benefit Plans Contributions (Details 14) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/NonqualifiedBenefitPlansContributionsDetails14 </Role>
<ShortName> Nonqualified Benefit Plans Contributions (Details 14) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 121 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R122.htm </HtmlFileName>
<LongName> 241084069 - Disclosure - Nonqualified Benefit Plans Investments (Details 15) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/NonqualifiedBenefitPlansInvestmentsDetails15 </Role>
<ShortName> Nonqualified Benefit Plans Investments (Details 15) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 122 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R123.htm </HtmlFileName>
<LongName> 241094070 - Disclosure - Defined Contribution Benefit Plans Contribution (Details 16) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/DefinedContributionBenefitPlansContributionDetails16 </Role>
<ShortName> Defined Contribution Benefit Plans Contribution (Details 16) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 123 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R124.htm </HtmlFileName>
<LongName> 241104071 - Disclosure - Multiemployer Plans Zones (Details 17) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/MultiemployerPlansZonesDetails17 </Role>
<ShortName> Multiemployer Plans Zones (Details 17) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 124 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R125.htm </HtmlFileName>
<LongName> 241114072 - Disclosure - Multiemployer Plans Participation by Plan (Details 18) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/MultiemployerPlansParticipationbyPlanDetails18 </Role>
<ShortName> Multiemployer Plans Participation by Plan (Details 18) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 125 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R126.htm </HtmlFileName>
<LongName> 241124073 - Disclosure - Multiemployer Plan Contributions (Details 19) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/MultiemployerPlanContributionsDetails19 </Role>
<ShortName> Multiemployer Plan Contributions (Details 19) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 126 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R127.htm </HtmlFileName>
<LongName> 241154074 - Disclosure - Jointly owned facilities (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/JointlyownedfacilitiesDetails </Role>
<ShortName> Jointly owned facilities (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<ParentRole> http://www.mdu.com/role/JointlyownedfacilitiesTables </ParentRole>
<Position> 127 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R128.htm </HtmlFileName>
<LongName> 241174075 - Disclosure - MNPUC (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/MNPUCDetails </Role>
<ShortName> MNPUC (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 128 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R129.htm </HtmlFileName>
<LongName> 241184076 - Disclosure - NDPSC (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/NDPSCDetails2 </Role>
<ShortName> NDPSC (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 129 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R130.htm </HtmlFileName>
<LongName> 241194077 - Disclosure - SDPUC (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/SDPUCDetails3 </Role>
<ShortName> SDPUC (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 130 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R131.htm </HtmlFileName>
<LongName> 241204078 - Disclosure - WUTC (Details 4) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/WUTCDetails4 </Role>
<ShortName> WUTC (Details 4) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 131 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R132.htm </HtmlFileName>
<LongName> 241214079 - Disclosure - FERC (Details 5) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/FERCDetails5 </Role>
<ShortName> FERC (Details 5) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 132 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R133.htm </HtmlFileName>
<LongName> 241254080 - Disclosure - Litigation (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/LitigationDetails </Role>
<ShortName> Litigation (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 133 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R134.htm </HtmlFileName>
<LongName> 241264081 - Disclosure - Enviromental matters (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/EnviromentalmattersDetails2 </Role>
<ShortName> Enviromental matters (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 134 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R135.htm </HtmlFileName>
<LongName> 241274082 - Disclosure - Purchase commitments (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/PurchasecommitmentsDetails3 </Role>
<ShortName> Purchase commitments (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 135 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R136.htm </HtmlFileName>
<LongName> 241284083 - Disclosure - Guarantees (Details 4) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/GuaranteesDetails4 </Role>
<ShortName> Guarantees (Details 4) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 136 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R137.htm </HtmlFileName>
<LongName> 241294084 - Disclosure - Variable interest entities (Details 5) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/VariableinterestentitiesDetails5 </Role>
<ShortName> Variable interest entities (Details 5) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 137 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R138.htm </HtmlFileName>
<LongName> 241314085 - Disclosure - Condensed Statements of Income and Comprehensive Income (Details) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CondensedStatementsofIncomeandComprehensiveIncomeDetails </Role>
<ShortName> Condensed Statements of Income and Comprehensive Income (Details) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 138 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R139.htm </HtmlFileName>
<LongName> 241324086 - Disclosure - Condensed Balance Sheets (Details 2) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CondensedBalanceSheetsDetails2 </Role>
<ShortName> Condensed Balance Sheets (Details 2) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 139 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R140.htm </HtmlFileName>
<LongName> 241334087 - Disclosure - Condensed Statements of Cash Flows (Details 3) </LongName>
<ReportType> Sheet </ReportType>
<Role> http://www.mdu.com/role/CondensedStatementsofCashFlowsDetails3 </Role>
<ShortName> Condensed Statements of Cash Flows (Details 3) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 140 </Position>
</Report>
<Report instance="mdu-20211231.htm">
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<HtmlFileName> R141.htm </HtmlFileName>
<LongName> 241344088 - Disclosure - Notes to Condensed Financial Statements (Details 4) </LongName>
<ReportType> Notes </ReportType>
<Role> http://www.mdu.com/role/NotestoCondensedFinancialStatementsDetails4 </Role>
<ShortName> Notes to Condensed Financial Statements (Details 4) </ShortName>
<MenuCategory> Details </MenuCategory>
<Position> 141 </Position>
</Report>
<Report>
<IsDefault> false </IsDefault>
<HasEmbeddedReports> false </HasEmbeddedReports>
<LongName> All Reports </LongName>
<ReportType> Book </ReportType>
<ShortName> All Reports </ShortName>
</Report>
</MyReports>
<InputFiles>
<File doctype="10-K" original="mdu-20211231.htm"> mdu-20211231.htm </File>
<File> a2021ex10k.htm </File>
<File> a2021ex10m.htm </File>
<File> a2021ex10w.htm </File>
<File> a2021ex21.htm </File>
<File> a2021ex23.htm </File>
<File> a2021ex31a.htm </File>
<File> a2021ex31b.htm </File>
<File> a2021ex32.htm </File>
<File> a2021ex95.htm </File>
<File> mdu-20211231.xsd </File>
<File> mdu-20211231_cal.xml </File>
<File> mdu-20211231_def.xml </File>
<File> mdu-20211231_lab.xml </File>
<File> mdu-20211231_pre.xml </File>
</InputFiles>
<SupplementalFiles>
<File> mdu-20211231_g1.jpg </File>
<File> mdu-20211231_g10.jpg </File>
<File> mdu-20211231_g11.jpg </File>
<File> mdu-20211231_g12.jpg </File>
<File> mdu-20211231_g2.jpg </File>
<File> mdu-20211231_g3.jpg </File>
<File> mdu-20211231_g4.jpg </File>
<File> mdu-20211231_g5.jpg </File>
<File> mdu-20211231_g6.jpg </File>
<File> mdu-20211231_g7.jpg </File>
<File> mdu-20211231_g8.jpg </File>
<File> mdu-20211231_g9.jpg </File>
</SupplementalFiles>
<BaseTaxonomies>
<BaseTaxonomy items="2329"> http://fasb.org/us-gaap/2021-01-31 </BaseTaxonomy>
<BaseTaxonomy items="37"> http://xbrl.sec.gov/dei/2021q4 </BaseTaxonomy>
</BaseTaxonomies>
<HasPresentationLinkbase> true </HasPresentationLinkbase>
<HasCalculationLinkbase> true </HasCalculationLinkbase>
</FilingSummary>

3 Subsequent Filings that Reference this Filing

  As Of               Filer                 Filing    For·On·As Docs:Size             Issuer                      Filing Agent

 2/23/24  MDU Resources Group, Inc.         S-8         2/23/24    5:92K                                    Toppan Merrill/FA
 2/22/24  MDU Resources Group, Inc.         10-K       12/31/23  161:31M
 2/24/23  MDU Resources Group, Inc.         10-K       12/31/22  172:39M

22 Previous Filings that this Filing References

  As Of               Filer                 Filing    For·On·As Docs:Size             Issuer                      Filing Agent

11/04/21  MDU Resources Group, Inc.         10-Q        9/30/21  101:13M
 8/05/21  MDU Resources Group, Inc.         10-Q        6/30/21  100:12M
 5/06/21  MDU Resources Group, Inc.         10-Q        3/31/21   98:10M
 2/19/21  MDU Resources Group, Inc.         10-K       12/31/20  171:24M
11/12/20  MDU Resources Group, Inc.         8-K:5,9    11/12/20   14:486K
 5/08/20  MDU Resources Group, Inc.         10-Q        3/31/20  101:11M
 2/21/20  MDU Resources Group, Inc.         10-K       12/31/19  169:27M
11/01/19  MDU Resources Group, Inc.         10-Q        9/30/19  116:15M
 8/02/19  MDU Resources Group, Inc.         10-Q        6/30/19  118:14M
 5/08/19  MDU Resources Group, Inc.         8-K:5,9     5/07/19    3:123K
 2/22/19  MDU Resources Group, Inc.         10-K       12/31/18  158:25M
 2/15/19  MDU Resources Group, Inc.         8-K:5,9     2/14/19    2:1M
 9/21/17  MDU Resources Group, Inc.         8-K:5,9     9/15/17    3:283K
 8/04/17  MDU Resources Group, Inc.         10-Q        6/30/17   90:9.8M
 2/19/16  MDU Resources Group, Inc.         10-K       12/31/15  157:23M
 5/15/14  MDU Resources Group, Inc.         8-K:1,5,9   5/15/14    4:459K
 2/21/14  MDU Resources Group, Inc.         10-K       12/31/13  156:29M
 8/07/12  MDU Resources Group, Inc.         10-Q        6/30/12   70:10M
 8/05/11  MDU Resources Group, Inc.         10-Q        6/30/11   63:10M
 2/17/10  MDU Resources Group, Inc.         10-K       12/31/09   61:12M
 8/07/08  MDU Resources Group, Inc.         10-Q        6/15/08   10:2.6M
 1/21/04  MDU Resources Group, Inc.         S-8         1/21/04    7:911K                                   Dewey & Leboeuf LLP
↑Top
Filing Submission 0000067716-22-000012   –   Alternative Formats (Word / Rich Text, HTML, Plain Text, et al.)
Copyright © 2024 Fran Finnegan & Company LLC – All Rights Reserved.
About — Privacy — Redactions — Help — Fri., May 17, 6:23:34.2pm ET