XML 84 R99.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Fair value - pensions (Details 9) (Pension Benefits, USD $) | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | $ 309,184,000 |  | $ 278,000,000 |  | $ 277,598,000
Percentage investment in common stock of mid-cap U.S. companies | 12.00% |  | 26.00% |  |
Percentage investment in common stock of large-cap U.S. companies | 26.00% |  | 26.00% |  |
Percentage investment in US Treasuries | 13.00% |  | 13.00% |  |
Percentage investment in corporate bonds | 41.00% |  | 6.00% |  |
Percentage investment in other investments | 8.00% |  | 29.00% |  |
Estimated future employer contributions in next fiscal year | 18,100,000 |  |  |  |
Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 12,605,000 |  | 19,790,000 |  |
Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 86,981,000 |  | 99,315,000 |  |
Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 39,818,000 |  | 35,353,000 |  |
Collective and Mutual funds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 102,852,000 | [1] | 58,755,000 | [2] |
Corporate debt securities [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 45,112,000 |  | 23,868,000 |  |
Mortgage-backed securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year |  |  | 22,987,000 |  |
Municipal bonds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 9,302,000 |  | 9,290,000 |  |
U.S. Treasury securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 12,514,000 |  | 8,642,000 |  |
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 219,711,000 |  | 180,138,000 |  |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 2,145,000 |  | 2,256,000 |  |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 86,981,000 |  | 99,315,000 |  |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 39,818,000 |  | 35,353,000 |  |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Collective and Mutual funds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 82,787,000 | [1] | 43,214,000 | [2] |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage-backed securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year |  |  | 0 |  |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 7,980,000 |  | 0 |  |
Significant Other Observable Inputs (Level 2) |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 89,473,000 |  | 97,573,000 |  |
Significant Other Observable Inputs (Level 2) | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 10,460,000 |  | 17,534,000 |  |
Significant Other Observable Inputs (Level 2) | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Significant Other Observable Inputs (Level 2) | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Significant Other Observable Inputs (Level 2) | Collective and Mutual funds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 20,065,000 | [1] | 15,541,000 | [2] |
Significant Other Observable Inputs (Level 2) | Corporate debt securities [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 45,112,000 |  | 23,579,000 |  |
Significant Other Observable Inputs (Level 2) | Mortgage-backed securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year |  |  | 22,987,000 |  |
Significant Other Observable Inputs (Level 2) | Municipal bonds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 9,302,000 |  | 9,290,000 |  |
Significant Other Observable Inputs (Level 2) | U.S. Treasury securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 4,534,000 |  | 8,642,000 |  |
Significant Unobservable Inputs (Level 3) |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 289,000 |  |
Significant Unobservable Inputs (Level 3) | Cash equivalents |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Significant Unobservable Inputs (Level 3) | Equity securities of U.S. companies |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Significant Unobservable Inputs (Level 3) | Equities Securities of International companies [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Significant Unobservable Inputs (Level 3) | Collective and Mutual funds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 | [1] | 0 | [2] |
Significant Unobservable Inputs (Level 3) | Corporate debt securities [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 289,000 |  |
Significant Unobservable Inputs (Level 3) | Mortgage-backed securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year |  |  | 0 |  |
Significant Unobservable Inputs (Level 3) | Municipal bonds [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | 0 |  | 0 |  |
Significant Unobservable Inputs (Level 3) | U.S. Treasury securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Fair value of net plan assets at end of year | $ 0 |  | $ 0 |  |
[1] | Collective and mutual funds invest approximately 12 percent in common stock of mid-cap U.S. companies, 26 percent in common stock of large-cap U.S. companies, 13 percent in U.S. Treasuries, 41 percent in corporate bonds and 8 percent in other investments.
[2] | Collective and mutual funds invest approximately 26 percent in common stock of mid-cap U.S. companies, 26 percent in common stock of large-cap U.S. companies, 13 percent in U.S. Treasuries, 6 percent in corporate bonds and 29 percent in other investments.

X
- Definition Percentage investment in common stock of large-cap U.S. companies. + References No definition available. + Details
Name: | mdu_PercentageInvestmentInCommonStockOfLargeCapUSCompanies
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage investment in common stock of mid-cap U.S. companies. + References No definition available. + Details
Name: | mdu_PercentageInvestmentInCommonStockOfMidCapUSCompanies
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage investment in corporate bonds. + References No definition available. + Details
Name: | mdu_PercentageInvestmentInCorporateBonds
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage investment in other investments. + References No definition available. + Details
Name: | mdu_PercentageInvestmentInOtherInvestments
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage investment in U.S. Treasuries. + References No definition available. + Details
Name: | mdu_PercentageInvestmentInUsTreasuries
Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The employer's best estimate, as soon as it can be reasonably determined, of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position. Estimated contributions may be presented in the aggregate combining (1) contributions required by funding regulations or laws, (2) discretionary contributions, and (3) noncash contributions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph g -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_DefinedBenefitPlanEstimatedFutureEmployerContributionsInNextFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=6867990&loc=d3e12355-114930 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 87 -Paragraph 49 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph d(iv)(b)(i) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant