Subsequent Events (Details) (USD $)	6 Months Ended		1 Months Ended		1 Months Ended
	Jun. 30, 2012	Jul. 02, 2012 Equitrans	Jul. 31, 2012 EQT Midstream Partners	Jul. 02, 2012 EQT Midstream Partners	Jul. 31, 2012 Initial public offering of common units	Jul. 31, 2012 Initial public offering of common units Equitrans	Jul. 02, 2012 Swing line loans
Subsequent Events
Number of common units issued to the public in an offering (in shares)			14,375,000			14,375,000
Common units issued to the public in an offering as a percentage of outstanding equity			40.60%			40.60%
Ownership percentage			59.40%		59.40%
Common units (in shares)				2,964,718
Subordinated units (in shares)				17,339,718
General partner's interest (as a percent)			2.00%		2.00%
Percentage of ownership contributed		100.00%
Net cash received upon closing of the IPO					$ 278,000,000
Proceeds distributed to EQT					232,000,000
Amount retained to replenish amounts distributed by Equitrans to EQT					12,000,000
Amount retained to pre-fund maintenance capital expenditures					32,000,000
Revolving credit facility origination fees	2,158,000				2,000,000
Maximum borrowing capacity							$ 350,000,000