Capitalized interest costs, period costs.

No definition available.

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- Definition

Cumulative interest costs incurred that are capitalized as of the balance-sheet date.

+ References

No definition available.

+ Details

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- Definition

Discount rate used in calculating the present value of future net cash flows from proved reserves as mandated under the rules of the SEC.

+ References

No definition available.

+ Details

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- Definition

The dollar amount that would have been charged to income after tax had the effects of the cash flow hedges not been considered in calculating the ceiling limitation at an oil and gas producing company subject to the full cost rules.

+ References

No definition available.

+ Details

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- Definition

Henry Hub natural gas price used to calculate the ceiling test.

+ References

No definition available.

+ Details

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- Definition

The after tax expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced.

+ References

No definition available.

+ Details

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- Details

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- Definition

NYMEX oil price used to calculate the ceiling test

+ References

No definition available.

+ Details

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- Definition

Time period for evaluating the majority of costs not subject to amortization and including the costs in the amortization base as the properties are evaluated and/or developed.

+ References

No definition available.

+ Details

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- Definition

Ventura natural gas prices used to calculate the celling test.

+ References

No definition available.

+ Details

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- Definition

The capitalized costs incurred during the period (excluded from amortization) to purchase, lease or otherwise acquire an unproved property, including costs of lease bonuses and options to purchase or lease properties, the portion of costs applicable to minerals when land including mineral rights is purchased in fee, brokers' fees, recording fees, legal costs, and other costs incurred in acquiring properties.

+ References

Reference 1: 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.(c)(7)(ii))

-URI http://asc.fasb.org/extlink&oid=27015464&loc=d3e511914-122862

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 10

-Paragraph c

-Subparagraph 3(ii)(A)

-Article 4

+ Details

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- Definition

The capitalized costs incurred (excluded from amortization), as of the date of the balance sheet, to purchase, lease or otherwise acquire an unproved property, including costs of lease bonuses and options to purchase or lease properties, the portion of costs applicable to minerals when land including mineral rights is purchased in fee, brokers' fees, recording fees, legal costs, and other costs incurred in acquiring properties.

+ References

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

The sum of the capitalized costs incurred during the period of unproved properties excluded from amortization including acquisition costs, exploration costs, development costs, and production costs.

+ References

+ Details

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- Definition

The sum of the capitalized costs incurred, as of the balance sheet date, of unproved properties excluded from amortization including acquisition costs, exploration costs, development costs, and production costs.

+ References

+ Details

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- Definition

The capitalized costs incurred during the period (excluded from amortization) to obtain access to proved reserves and to provide facilities for extracting, treating, gathering and storing the oil and gas.

+ References

+ Details

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- Definition

The capitalized costs incurred (excluded from amortization), as of the date of the balance sheet, to obtain access to proved reserves and to provide facilities for extracting, treating, gathering and storing the oil and gas.

+ References

+ Details

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- Definition

Amount that would have been charged to income had the effects of the cash flow hedges not been considered in calculating the ceiling limitation at an oil and gas producing company subject to the full cost rules.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 360

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 12.D.3(b))

-URI http://asc.fasb.org/extlink&oid=27015634&loc=d3e516453-122869

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 12

-Section D

-Paragraph b

-Subsection 3

+ Details

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- Definition

The capitalized costs incurred during the period (excluded from amortization) in identifying areas that may warrant examination and in examining specific areas that are considered to have prospects of containing oil and gas reserves, including costs of drilling exploratory wells and exploratory-type stratigraphic test wells. Exploration costs may be incurred both before acquiring the related property (sometimes referred to in part as prospecting costs) and after acquiring the property. Principal types of exploration costs, which include depreciation and applicable operating costs of support equipment and facilities and other costs of exploration activities, are: costs of topographical, geographical and geophysical studies, rights of access to properties to conduct those studies, and salaries and other expenses of geologists, geophysical crews, and others conducting those studies. Collectively, these are sometimes referred to as geological and geophysical or "G&G" costs. Exploration costs also include costs of carrying and retaining undeveloped properties, such as delay rentals, ad valorem taxes on properties, legal costs for title defense, the maintenance of land and lease records, dry hole contributions and bottom hole contributions, costs of drilling and equipping exploratory wells and costs of drilling exploratory-type stratigraphic test wells.

+ References

+ Details

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- Definition

The capitalized costs incurred (excluded from amortization), as of the date of the balance sheet, in identifying areas that may warrant examination and in examining specific areas that are considered to have prospects of containing oil and gas reserves, including costs of drilling exploratory wells and exploratory-type stratigraphic test wells. Exploration costs may be incurred both before acquiring the related property (sometimes referred to in part as prospecting costs) and after acquiring the property. Principal types of exploration costs, which include depreciation and applicable operating costs of support equipment and facilities and other costs of exploration activities, are: costs of topographical, geographical and geophysical studies, rights of access to properties to conduct those studies, and salaries and other expenses of geologists, geophysical crews, and others conducting those studies. Collectively, these are sometimes referred to as geological and geophysical or "G&G" costs. Exploration costs also include costs of carrying and retaining undeveloped properties, such as delay rentals, ad valorem taxes on properties, legal costs for title defense, the maintenance of land and lease records, dry hole contributions and bottom hole contributions, costs of drilling and equipping exploratory wells and costs of drilling exploratory-type stratigraphic test wells.

+ References

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- Definition

The expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 360

-Section 35

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=28370743&loc=d3e66150-109466

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6391110&loc=d3e2921-110230

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Oil and natural gas properties (Details 6) (USD $)	3 Months Ended		12 Months Ended
Oil and natural gas properties (Details 6) (USD $)	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Feb. 01, 2015	Jan. 01, 2015
Natural gas and oil properties [Abstract]
Discount rate used in calculating present value of future net cash flows from proved reserves (in hundredths)			10.00%
NYMEX oil price	94.71mdu_NymexOilPrice	94.97mdu_NymexOilPrice	94.99mdu_NymexOilPrice		94.71mdu_NymexOilPrice		99.08mdu_NymexOilPrice	100.27mdu_NymexOilPrice	98.46mdu_NymexOilPrice
Henry Hub natural gas price	2.76mdu_HenryHubNaturalGasPrice	2.83mdu_HenryHubNaturalGasPrice	4.34mdu_HenryHubNaturalGasPrice		2.76mdu_HenryHubNaturalGasPrice		4.24mdu_HenryHubNaturalGasPrice	4.10mdu_HenryHubNaturalGasPrice	3.99mdu_HenryHubNaturalGasPrice
Ventura natural gas price			7.71mdu_VenturaNaturalGasPrice				7.60mdu_VenturaNaturalGasPrice	7.47mdu_VenturaNaturalGasPrice	7.33mdu_VenturaNaturalGasPrice
Write-downs of oil and natural gas properties	$ 231,700,000us-gaap_ImpairmentOfOilAndGasProperties	$ 160,100,000us-gaap_ImpairmentOfOilAndGasProperties	$ 0us-gaap_ImpairmentOfOilAndGasProperties	$ 0us-gaap_ImpairmentOfOilAndGasProperties	$ 391,800,000us-gaap_ImpairmentOfOilAndGasProperties
Noncash write-downs of oil and natural gas properties, after tax	145,900,000	100,900,000			246,800,000
Additional write-downs of its oil and natural gas properties that would have been recognized without effects of cash flow hedges	20,800,000	19,500,000			20,800,000
Additional write-downs of its oil and natural gas properties that would have been recognized without effects of cash flow hedges, after tax	13,100,000	12,300,000			13,100,000
Oil and natural gas properties not subject to amortization [Abstract]
Acquisition			97,795,000us-gaap_AcquisitionCostsCumulative
Development			14,312,000us-gaap_DevelopmentCostsCumulative
Exploration			18,221,000us-gaap_ExplorationCostsCumulative
Capitalized interest			1,813,000mdu_CapitalizedInterestCumulative
Total costs not subject to amortization	191,794,000		132,141,000	124,869,000	191,794,000
Acquisition costs, period cost			82,233,000us-gaap_AcquisitionCosts	1,528,000us-gaap_AcquisitionCosts	475,000us-gaap_AcquisitionCosts	13,559,000us-gaap_AcquisitionCosts
Development costs, period cost			3,361,000us-gaap_DevelopmentCosts	9,928,000us-gaap_DevelopmentCosts	484,000us-gaap_DevelopmentCosts	539,000us-gaap_DevelopmentCosts
Exploration costs, period cost			10,961,000us-gaap_ExplorationCosts	3,126,000us-gaap_ExplorationCosts	3,885,000us-gaap_ExplorationCosts	249,000us-gaap_ExplorationCosts
Capitalized interest costs, period costs			1,343,000mdu_CapitalizedInterestCostsPeriodCosts	203,000mdu_CapitalizedInterestCostsPeriodCosts	67,000mdu_CapitalizedInterestCostsPeriodCosts	200,000mdu_CapitalizedInterestCostsPeriodCosts
Capitalized costs of unproved properties excluded from amortization, period cost			$ 97,898,000	$ 14,785,000	$ 4,911,000	$ 14,547,000
Time period for evaluating majority of costs not subject to amortization			5 years
Subsequent Event [Member]
Natural gas and oil properties [Abstract]
NYMEX oil price										48.24	53.27
Henry Hub natural gas price										2.68	3.00
Ventura natural gas price										2.78	3.06