Name:	str_AgreementLineItems
Namespace Prefix:	str_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The after tax average rate of return from operations under the agreement.

+ References

No definition available.

+ Details

Name:	str_AverageAnnualRateOfReturnAfterTax
Namespace Prefix:	str_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Net investment base of the subsidiary.

+ References

No definition available.

+ Details

Name:	str_NetInvestmentBase
Namespace Prefix:	str_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of operating income received by subsidiary from operations as outlined by the agreement.

+ References

No definition available.

+ Details

Name:	str_OilIncomeSharingAmountsPerAgreement
Namespace Prefix:	str_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The percentage of after-tax return allowed to subsidiary from operations as outlined by the agreement.

+ References

No definition available.

+ Details

Name:	str_PercentageOfAfterTaxRateOfReturn
Namespace Prefix:	str_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of operating income retained by the subsidiary from operations as outlined by agreement.

+ References

No definition available.

+ Details

Name:	str_PercentageOfOperatingIncomeRetention
Namespace Prefix:	str_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of operating income retained by subsidiary from operations as outlined by agreement that are other than Wexpro.

+ References

No definition available.

+ Details

Name:	str_PercentageOfOperatingIncomeRetentionGas
Namespace Prefix:	str_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The rate-of-return premium relative to a group of regulated companies' returns allowed to subsidiary from operations as outlined by the agreement.

+ References

No definition available.

+ Details

Name:	str_PercentageofPremiumAddedtoBaseAfterTaxRateofReturn
Namespace Prefix:	str_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

To the extent the Questar Gas supply provided by Wexpro I properties plus Trail acquisition properties exceeds 65%, special treatment is required such that Questar Gas customers pay the lower of Questar Gas purchased-gas price or Wexpro cost-of-service price on the incremental volumes.

+ References

No definition available.

+ Details

Name:	str_TrailAcquisitionSpecifiedQuestarGasSupplyPercentage
Namespace Prefix:	str_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	str_MajorProvisionsOfAgreementAxis=str_CrudeOilProductionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	str_MajorProvisionsOfAgreementAxis=str_DevelopmentalOilDrillingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	str_MajorProvisionsOfAgreementAxis=str_GasDevelopmentDrillingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	str_MajorProvisionsOfAgreementAxis=str_NaturalGasOperationsMember
Namespace Prefix:
Data Type:	na
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Wexpro and Wexpro II Agreements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Agreement [Line Items]
Percentage of Wexpro retention (in hundredths)	46.00%
Wexpro net investment base at December 31, (in millions)	$ 649.0str_NetInvestmentBase	$ 589.7str_NetInvestmentBase	$ 531.1str_NetInvestmentBase
Average annual rate of return (after tax) (in hundredths)	17.90%str_AverageAnnualRateOfReturnAfterTax	19.70%str_AverageAnnualRateOfReturnAfterTax	19.90%str_AverageAnnualRateOfReturnAfterTax
Oil and NGL income sharing (in millions)	$ 0str_OilIncomeSharingAmountsPerAgreement	$ 0.6str_OilIncomeSharingAmountsPerAgreement	$ 2.5str_OilIncomeSharingAmountsPerAgreement
Trail acquisition specified Questar Gas supply percentage (in hundredths)	65.00%
Gas-development drilling [Member]
Agreement [Line Items]
Percentage of Wexpro after-tax rate of return (in hundredths)	20.00%
Percentage of premium added to base after-tax rate of return (in hundredths)	8.00%
Natural gas operations [Member]
Agreement [Line Items]
Percentage of Wexpro after-tax rate of return (in hundredths)	12.00%
Developmental oil drilling [Member]
Agreement [Line Items]
Percentage of Wexpro after-tax rate of return (in hundredths)	17.00%
Percentage of premium added to base after-tax rate of return (in hundredths)	5.00%
Percentage of Wexpro retention (in hundredths)	46.00%
Percentage of Questar Gas retention (in hundredths)	54.00%
Crude oil production [Member]
Agreement [Line Items]
Percentage of Wexpro after-tax rate of return (in hundredths)	12.00%
Percentage of Wexpro retention (in hundredths)	46.00%
Acquired natural gas production [Member]
Agreement [Line Items]
Percentage of Wexpro after-tax rate of return (in hundredths)	7.60%