XML 122 R120.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Estimated quanities of proved reserves (Details 5) | 12 Months Ended
--- | ---
Dec. 31, 2012 MBoe | Dec. 31, 2011 MBoe | Dec. 31, 2010 MBoe
Proved developed and undeveloped reserves: |  |  |
Balance at beginning of year, BOE | 97,651 | 107,599 | 108,954
Production, BOE | (10,058) | (11,099) | (11,661)
Extensions and discoveries, BOE | 14,756 | 10,842 | 9,421
Improved recovery, BOE | 0 | 0 | 0
Purchases of proved reserves, BOE | 0 | 247 | 10,165
Sales of proved reserves, BOE | (423) | 0 | (34)
Revisions of previous estimates, BOE | (21,440) | (9,938) | (9,246)
Balance at end of year, BOE | 80,486 | 97,651 | 107,599
Reduction in proved undeveolped reserves specified properties |  | 8,900 |
Oil (MBbls) |  |  |
Proved developed and undeveloped reserves: |  |  |
Balance at beginning of year | 27,005 | 25,666 | 25,930
Production | (3,694) | (2,724) | (2,767)
Extensions and discoveries | 9,874 | 4,717 | 2,793
Improved recovery | 0 | 0 | 0
Purchases of proved reserves | 0 | 223 | 911
Sales of proved reserves | (39) | 0 | (18)
Revisions of previous estimates | 307 | (877) | (1,183)
Balance at end of year | 33,453 | 27,005 | 25,666
NGL (MBbls) |  |  |
Proved developed and undeveloped reserves: |  |  |
Balance at beginning of year | 7,342 | 7,201 | 8,286
Production | (828) | (776) | (495)
Extensions and discoveries | 1,817 | 1,421 | 596
Improved recovery | 0 | 0 | 0
Purchases of proved reserves | 0 | 16 | 68
Sales of proved reserves | 0 | 0 | 0
Revisions of previous estimates | (1,178) | (520) | (1,254)
Balance at end of year | 7,153 | 7,342 | 7,201
Natural Gas (MMcf) |  |  |
Proved developed and undeveloped reserves: |  |  |
Balance at beginning of year | 379,827 | 448,397 | 448,425
Production | (33,214) | (45,598) | (50,391)
Extensions and discoveries | 18,386 | 28,221 | 36,191
Improved recovery | 0 | 0 | 0
Purchases of proved reserves | 0 | 54 | 55,119
Sales of proved reserves | (2,307) | 0 | (92)
Revisions of previous estimates | (123,414) | (51,247) | (40,855)
Balance at end of year | 239,278 | 379,827 | 448,397

X
- Definition Additions to proved reserves that result from (1) extension of the proved acreage of previously discovered (old) reservoirs through additional drilling in periods after discovery and (2) discovery of new fields with proved reserves or of new reservoirs of proved reserves in old fields, BOE. + References No definition available. + Details
Name: | mdu_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditionsBoe
Namespace Prefix: | mdu_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | duration

X
- Definition Changes in proved reserve estimates resulting from application of improved recovery techniques, BOE. + References No definition available. + Details
Name: | mdu_ProvedDevelopedAndUndevelopedReservesImprovedRecoveryBoe
Namespace Prefix: | mdu_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | duration

X
- Definition The net quantity of proved reserves as of the balance sheet date. Proved oil reserves are the estimated quantities of crude oil and natural gas liquids which geological and engineering data demonstrate with reasonable certainty to be recoverable, BOE. + References No definition available. + Details
Name: | mdu_ProvedDevelopedAndUndevelopedReservesNetBoe
Namespace Prefix: | mdu_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | instant

X
- Definition Production of proved reserves, BOE. + References No definition available. + Details
Name: | mdu_ProvedDevelopedAndUndevelopedReservesProductionBoe
Namespace Prefix: | mdu_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | duration

X
- Definition Purchase of minerals in place, BOE. + References No definition available. + Details
Name: | mdu_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlaceBoe
Namespace Prefix: | mdu_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | duration

X
- Definition Revisions represent changes in previous estimates of proved reserves, either upward or downward, resulting from new information (except for an increase in proved acreage) normally obtained from development drilling and production history or resulting from change in economic factors, BOE. + References No definition available. + Details
Name: | mdu_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesBoe
Namespace Prefix: | mdu_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | duration

X
- Definition Sales of minerals in place, BOE. + References No definition available. + Details
Name: | mdu_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlaceBoe
Namespace Prefix: | mdu_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | duration

X
- Definition Reduction in proved undeveolped reserves specified properties. + References No definition available. + Details
Name: | mdu_ReductionInProvedUndeveolpedReservesSpecifiedProperties
Namespace Prefix: | mdu_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Additions to proved reserves that result from (1) extension of the proved acreage of previously discovered (old) reservoirs through additional drilling in periods after discovery and (2) discovery of new fields with proved reserves or of new reservoirs of proved reserves in old fields. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61831-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -Subparagraph d -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_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
Namespace Prefix: | us-gaap_
Data Type: | num:volumeItemType
Balance Type: | na
Period Type: | duration

X
- Definition Changes in proved reserve estimates resulting from application of improved recovery techniques. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61831-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -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. + Details
Name: | us-gaap_ProvedDevelopedAndUndevelopedReservesImprovedRecovery
Namespace Prefix: | us-gaap_
Data Type: | num:volumeItemType
Balance Type: | na
Period Type: | duration

X
- Definition The net quantity of proved reserves as of the balance sheet date. Proved oil reserves are the estimated quantities of crude oil and natural gas liquids which geological and engineering data demonstrate with reasonable certainty to be recoverable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 10 -Paragraph a -Subparagraph 2 -Article 4 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61831-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-10.(a)(2)) -URI http://asc.fasb.org/extlink&oid=21918352&loc=d3e511914-122862 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -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_ProvedDevelopedAndUndevelopedReservesNet
Namespace Prefix: | us-gaap_
Data Type: | num:volumeItemType
Balance Type: | na
Period Type: | instant

X
- Definition Production of proved reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61831-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -Subparagraph e -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_ProvedDevelopedAndUndevelopedReservesProduction
Namespace Prefix: | us-gaap_
Data Type: | num:volumeItemType
Balance Type: | na
Period Type: | duration

X
- Definition Purchase of minerals in place. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61831-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -Subparagraph c -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_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
Namespace Prefix: | us-gaap_
Data Type: | num:volumeItemType
Balance Type: | na
Period Type: | duration

X
- Definition Revisions represent changes in previous estimates of proved reserves, either upward or downward, resulting from new information (except for an increase in proved acreage) normally obtained from development drilling and production history or resulting from change in economic factors. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61831-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -Subparagraph a -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_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
Namespace Prefix: | us-gaap_
Data Type: | num:volumeItemType
Balance Type: | na
Period Type: | duration

X
- Definition Sales of minerals in place. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61831-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -Subparagraph f -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_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
Namespace Prefix: | us-gaap_
Data Type: | num:volumeItemType
Balance Type: | na
Period Type: | duration