XML 36 R73.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Credit facilities (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2012 | Dec. 31, 2011
Line of credit facility and other debt [Abstract] |  |  |  |
Letters of credit at end of period | $ 25.0 |  |  |
Long-term debt [Member] | Commercial paper revolving credit agreement [Member] | MDU Resources Group, Inc [Member] |  |  |  |
Line of credit facility and other debt [Abstract] |  |  |  |
Facility limit | 125.0 |  |  |
Amount outstanding, end of period | 76.0 | [1] | 0 | [1]
Expiration date | Oct. 04, 2017 |  |  |
Long-term debt [Member] | Commercial paper revolving credit agreement [Member] | Centennial Energy Holdings, Inc [Member] |  |  |  |
Line of credit facility and other debt [Abstract] |  |  |  |
Facility limit | 500.0 |  |  |
Amount outstanding, end of period | 217.0 | [1] | 0 | [1]
Expiration date | Jun. 08, 2017 |  |  |
Long-term debt [Member] | Revolving credit agreement [Member] | MDU Resources Group, Inc [Member] |  |  |  |
Line of credit facility and other debt [Abstract] |  |  |  |
Letters of credit at end of period | 0 |  |  |
Commercial paper program supported by revolving credit agreement with various banks | 125 |  |  |
Revolving credit agreement | 125 |  |  |
Option to increase borrowings, maximum amount | 150 |  |  |
Long-term debt [Member] | Revolving credit agreement [Member] | Centennial Energy Holdings, Inc [Member] |  |  |  |
Line of credit facility and other debt [Abstract] |  |  |  |
Letters of credit at end of period | 20.2 | [2] |  |
Commercial paper program supported by revolving credit agreement with various banks | 500 |  |  |
Revolving credit agreement | 500 |  |  |
Option to increase borrowings, maximum amount | 650 |  |  |
Short-term debt [Member] | Revolving credit agreement [Member] | Cascade Natural Gas Corporation [Member] |  |  |  |
Line of credit facility and other debt [Abstract] |  |  |  |
Facility limit | 50.0 | [3] |  |
Amount outstanding, end of period | 2.0 |  | 0 |
Letters of credit at end of period | 0 |  |  |
Expiration date | Dec. 27, 2013 |  |  |
Option to increase borrowings, maximum amount | 75 |  |  |
Short-term debt [Member] | Revolving credit agreement [Member] | Intermountain Gas Company [Member] |  |  |  |
Line of credit facility and other debt [Abstract] |  |  |  |
Facility limit | 65.0 | [4] |  |
Amount outstanding, end of period | 26.2 |  | 8.1 |
Letters of credit at end of period | 0 |  |  |
Expiration date | Aug. 11, 2013 |  |  |
Option to increase borrowings, maximum amount | $ 80 |  |  |
[1] | Amount outstanding under commercial paper program
[2] | The outstanding letters of credit, as discussed in Note 19, reduce amounts available under the credit agreement.
[3] | Certain provisions allow for increased borrowings, up to a maximum of $75 million.
[4] | Certain provisions allow for increased borrowings, up to a maximum of $80 million.

X
- Definition Commercial paper program supported by revolving credit agreement with various banks. + References No definition available. + Details
Name: | mdu_CommercialPaperProgramSupportedByRevolvingCreditAgreementWithVariousBanks
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Letters of credit. + References No definition available. + Details
Name: | mdu_LettersOfCredit
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The option to increase borrowing capacity to the stated maximum amount, at the option of the company, on stated conditions. + References No definition available. + Details
Name: | mdu_OptionToIncreaseBorrowingsMaximumAmount
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Revolving credit agreement + References No definition available. + Details
Name: | mdu_RevolvingCreditAgreement
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

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

X
- Definition Amount borrowed under the credit facility as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityAmountOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Date the credit facility terminates, in CCYY-MM-DD format. + References Reference 1: 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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant