Subsequent Events (Details) (USD $)	Jun. 30, 2013
Questar Gas [Member]
Questar Gas Utah General Rate Case [Abstract]
Amount of requested increase in rates in Utah	$ 19,000,000
Requested return on equity in Utah	10.35%
Expected timing of decision on Utah rate case	first quarter of 2014
Questar Gas [Member] | 4.78% and 4.83% Notes due 2043 and 2048 [Member]
Questar Gas Long-term Debt Commitment [Abstract]
Debt Instrument, Face Amount	150,000,000
Funding Date of Long-term Debt	December 2013
Questar Gas [Member] | 4.78% Notes due 2043 [Member]
Questar Gas Long-term Debt Commitment [Abstract]
Debt Instrument, Face Amount	90,000,000
Long-term Debt, Life (in years)	30 years
Debt Instrument, Interest Rate, Stated Percentage	4.78%
Questar Gas [Member] | 4.83% Notes due 2048 [Member]
Questar Gas Long-term Debt Commitment [Abstract]
Debt Instrument, Face Amount	60,000,000
Long-term Debt, Life (in years)	35 years
Debt Instrument, Interest Rate, Stated Percentage	4.83%
Wexpro [Member]
Wexpro Acquisition [Abstract]
Purchase price of assets acquired by Wexpro	$ 106,400,000