Summary of Significant Accounting Policies - Regulatory Accounting (Details) (EQT Midstream, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
EQT Midstream
Property, Plant and Equipment [Line Items]
Net Revenues	$ 267,997	$ 184,767	$ 131,184
Operating expenses	89,617	71,517	66,202
Property, plant & equipment	1,160,696	1,015,118
Accumulated depreciation and amortization	(188,884)	(158,533)
Net property, plant & equipment	$ 971,812	$ 856,585