Share-Based Compensation Stock option transactions, exercise price - (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011 Years	Dec. 31, 2010
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Unvested stock options decrease in period (in shares)		115,068
Stock-option transactions under the terms of the LTSIP [Roll Forward]
Options outstanding, beginning balance (in shares)	2,560,059
Granted (in shares)	0
Exercised (in shares)	(786,424)
Forfeited (in shares)	0
Options outstanding, ending balance (in shares)	1,773,635	2,560,059
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosures [Roll Forward]
Minimum exercise price of options outstanding, beginning of period (in dollars per share)	$ 3.70
Maximum exercise price of options outstanding, beginning of the period (in dollars per share)	$ 17.35
Minimum exercise price of options exercised during the period (in dollars per share)	$ 3.70
Maximum exercise price of options exercised during the period (in dollars per share)	$ 13.10
Minimum exercise price of options outstanding, end of period (in dollars per share)	$ 3.70	$ 3.70
Maximum exercise price of options outstanding, end of period (in dollars per share)	$ 17.35	$ 17.35
Weighted-average exercise price, options outstanding, beginning of period (in dollars per share)	$ 7.30
Weighted average exercise price of options exercised during the period (in dollars per share)	$ 4.49
Weighted-average exercise price, options outstanding, end of period (in dollars per share)	$ 8.54	$ 7.30
Weighted-average remaining term (in years)	2.4
Number of exercisable options at end of period	1,655,841
Weighted-average exercise price, options exercisable	$ 8.28
Number of unvested options at end of period	117,794
Weighted-average exercise price, unvested options	$ 12.25
Options Outstanding Exercise Price Range 1 [Member]
Stock-option transactions under the terms of the LTSIP [Roll Forward]
Options outstanding, ending balance (in shares)	791,261
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosures [Roll Forward]
Minimum exercise price of options outstanding, end of period (in dollars per share)	$ 3.70
Maximum exercise price of options outstanding, end of period (in dollars per share)	$ 4.37
Weighted-average exercise price, options outstanding, end of period (in dollars per share)	$ 4.29
Weighted-average remaining term (in years)	1.0
Number of exercisable options at end of period	791,261
Weighted-average exercise price, options exercisable	$ 4.29
Number of unvested options at end of period	0
Weighted-average exercise price, unvested options	$ 0.00
Options Outstanding Exercise Price Range 2 [Member]
Stock-option transactions under the terms of the LTSIP [Roll Forward]
Options outstanding, ending balance (in shares)	449,174
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosures [Roll Forward]
Minimum exercise price of options outstanding, end of period (in dollars per share)	$ 7.84
Maximum exercise price of options outstanding, end of period (in dollars per share)	$ 11.40
Weighted-average exercise price, options outstanding, end of period (in dollars per share)	$ 10.61
Weighted-average remaining term (in years)	3.9
Number of exercisable options at end of period	390,177
Weighted-average exercise price, options exercisable	$ 10.49
Number of unvested options at end of period	58,997
Weighted-average exercise price, unvested options	$ 11.40
Options Outstanding Exercise Price Range 3 [Member]
Stock-option transactions under the terms of the LTSIP [Roll Forward]
Options outstanding, ending balance (in shares)	533,200
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosures [Roll Forward]
Minimum exercise price of options outstanding, end of period (in dollars per share)	$ 12.43
Maximum exercise price of options outstanding, end of period (in dollars per share)	$ 17.35
Weighted-average exercise price, options outstanding, end of period (in dollars per share)	$ 13.11
Weighted-average remaining term (in years)	3.2
Number of exercisable options at end of period	474,403
Weighted-average exercise price, options exercisable	$ 13.11
Number of unvested options at end of period	58,797
Weighted-average exercise price, unvested options	$ 13.10
Questar Pipeline [Member]
Stock-option transactions under the terms of the LTSIP [Roll Forward]
Options outstanding, ending balance (in shares)	231,514
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosures [Roll Forward]
Minimum exercise price of options outstanding, end of period (in dollars per share)	$ 3.70
Maximum exercise price of options outstanding, end of period (in dollars per share)	$ 13.10
Weighted-average exercise price, options outstanding, end of period (in dollars per share)	$ 8.56
Weighted-average remaining term (in years)	3.1
Number of exercisable options at end of period	194,650
Weighted-average exercise price, options exercisable	$ 7.86
Number of unvested options at end of period	36,864
Weighted-average exercise price, unvested options	$ 12.25
Questar Gas [Member]
Stock-option transactions under the terms of the LTSIP [Roll Forward]
Options outstanding, ending balance (in shares)	99,046
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosures [Roll Forward]
Minimum exercise price of options outstanding, end of period (in dollars per share)	$ 3.70
Maximum exercise price of options outstanding, end of period (in dollars per share)	$ 13.10
Weighted-average exercise price, options outstanding, end of period (in dollars per share)	$ 5.66
Weighted-average remaining term (in years)	1.6
Number of exercisable options at end of period	91,047
Weighted-average exercise price, options exercisable	$ 5.07
Number of unvested options at end of period	7,999
Weighted-average exercise price, unvested options	$ 12.39