XML 28 R37.htm IDEA: XBRL DOCUMENT v2.4.0.6

Oil and natural gas properties Oil and natural gas properties (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Oil and natural gas properties [Abstract]
Discount rate used in calculating present value of future net cash flows from proved reserves	10.00%		10.00%
Write-down of oil and natural gas properties	$ 160,100	$ 0	$ 160,100	$ 0
Write-down of oil and natural gas properties, after tax	100,900		100,900
Effects of cash flow hedges not considered in calculating ceiling limitation, amount	19,500		19,500
Effects of cash flow hedges not considered in calculating ceiling limitation amount, after tax	$ 12,300		$ 12,300

X

- 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

Name:	mdu_DiscountRateUsedInCalculatingPresentValueOfFutureNetCashFlowsFromProvedReserves
Namespace Prefix:	mdu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- 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

Name:	mdu_EffectsOfCashFlowHedgesNotConsideredInCalculatingCeilingLimitationAmountAfterTax
Namespace Prefix:	mdu_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

X

- 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

Name:	mdu_ImpairmentOfOilAndGasPropertiesAfterTax
Namespace Prefix:	mdu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	mdu_OilAndNaturalGasPropertiesAbstract
Namespace Prefix:	mdu_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- 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=6601679&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

Name:	us-gaap_EffectsOfCashFlowHedgesNotConsideredInCalculatingCeilingLimitationAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

X

- 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 Statement of Financial Accounting Standard (FAS)

-Number 19

-Paragraph 27, 28, 29

-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 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585



Reference 3: 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=6475018&loc=d3e66150-109466



Reference 4: 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

+ Details

Name:	us-gaap_ImpairmentOfOilAndGasProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration