Derivatives and Hedging (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Dec. 31, 2011	Dec. 31, 2014	Dec. 31, 2011	Mar. 31, 2014
Derivative [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$ 0		0		$ 0
Cash Flow Hedging [Member] | Questar Pipeline [Member] | Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]
Derivative [Line Items]
Notional amount		150,000,000		150,000,000
Debt Instrument, Face Amount		180,000,000		180,000,000
Interest payment for terminated derivative instrument		37,300,000
Life of long-term debt associated with cash flow hedges				30 years
Date Through Which Reclassifications Into Earnings From AOCI Will Take Place			2041
Pre-tax net losses expected to be reclassified from AOCI to Consolidated statement of income	$ 600,000
Reclassification from accumulated OCI to income, time to transfer	12 months