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Debt Long-term borrowings (Details 3) (Long-term debt [Member], USD $) In Millions, unless otherwise specified | Dec. 31, 2012
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MDU Resources Group, Inc [Member] | Revolving credit agreement [Member] |
Debt instrument [Line Items] |
Borrowing capacity of amended revolving credit agree | $ 125.0
Ratio of funded debt to total capitalization as specified in debt convenants | 65.00%
Ratio of funded debt to capitalization - Company alone, as specified in debt convenants | 65.00%
MDU Resources Group, Inc [Member] | Commercial paper revolving credit agreement [Member] |
Debt instrument [Line Items] |
Facility limit | 125.0
MDU Energy Capital, LLC [Member] | Master shelf agreement member [Member] |
Debt instrument [Line Items] |
Ratio of total debt to adjusted total capitalization as specified in debt convenants | 70.00%
Ratio of subsidiary debt to subsidiary capitalization as specified in debt convenants | 65.00%
Ratio of total debt to total capitalization as specified in debt convenants. | 65.00%
Ratio - EBIT to interest expense | 150.00%
MDU Energy Capital, LLC [Member] | Note purchase agreemnt [Member] |
Debt instrument [Line Items] |
Weighted average interest rate | 4.10%
Contracted issuance of senior notes | 25.0
Senior notes | 25.0
Centennial Energy Holdings, Inc [Member] | Revolving credit agreement [Member] |
Debt instrument [Line Items] |
Ratio of total debt to total capitalization as specified in debt convenants. | 65.00%
Centennial Energy Holdings, Inc [Member] | Master shelf agreement member [Member] |
Debt instrument [Line Items] |
Ratio of total debt to total capitalization as specified in debt convenants. | 60.00%
Ratio of EBITDA to Interest Expense | 175.00%
Centennial Energy Holdings, Inc [Member] | Note purchase agreemnt [Member] |
Debt instrument [Line Items] |
Issuance of senior notes | 150.0
Weighted average interest rate | 4.60%
Contracted issuance of senior notes | 100.0
Centennial Energy Holdings, Inc [Member] | Letter of credit [Member] |
Debt instrument [Line Items] |
Letters of credit | 29.0
Centennial Energy Holdings, Inc [Member] | Commercial paper revolving credit agreement [Member] |
Debt instrument [Line Items] |
Facility limit | $ 500.0
WBI Energy Transmission, Inc. [Member] | Uncommitted long-term private shelf agreement [Member] |
Debt instrument [Line Items] |
Ratio of total debt to total capitalization as specified in debt convenants. | 55.00%

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- Definition Contracted issuance of senior notes. + References No definition available. + Details
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- Definition Ratio of funded debt to total capitalization as specified in debt convenants. + References No definition available. + Details
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- Definition Ratio of subsidiary debt to subsidiary capitalization as specified in debt convenants. + References No definition available. + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 2, 4 -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
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- Definition Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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