Amount of natural gas bought under previous purchase agreements.

No definition available.

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

- Details

Name:	us-gaap_LongTermPurchaseCommitmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum amount of purchase arrangement maturing in the fifth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInFifthYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing in the fourth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInFourthYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing in the next fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing in the second fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInSecondYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing in the third fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInThirdYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Commitments, Contingencies and Leases Commitments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Questar Gas [Member]
Long-term Purchase Commitment [Line Items]
Natural gas purchased under agreements	$ 104.1	$ 221.0	$ 245.2
Questar Gas [Member] \| Gas purchase agreements [Member]
Long-term Purchase Commitment [Line Items]
2013	29.5
2014	16.0
2015	16.0
2016	16.1
2017	19.3
Questar Gas [Member] \| Transportation and storage commitments - Related party [Member]
Long-term Purchase Commitment [Line Items]
2013	73.0
2014	71.1
2015	71.1
2016	71.1
2017	44.5
Questar Gas [Member] \| Transportation and gathering commitments - Third party [Member]
Long-term Purchase Commitment [Line Items]
2013	27.9
2014	27.9
2015	27.9
2016	27.9
2017	27.9
Wexpro [Member] \| Well-drilling commitment [Member]
Long-term Purchase Commitment [Line Items]
2013	$ 0.7