Derivatives and Hedging (Details) - USD ($)	3 Months Ended	6 Months Ended	12 Months Ended
	Dec. 31, 2011	Jun. 30, 2015	Dec. 31, 2011	Dec. 31, 2014	Jun. 30, 2014
Derivative [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net		$ (300,000)		$ 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		$ 500,000
Reclassification from accumulated OCI to income, time to transfer		12 months