Acquisitions (Details) a in Thousands, Mcfe in Thousands, $ in Thousands			6 Months Ended
	Feb. 27, 2017 a Mcfe well mi	Feb. 01, 2017 a	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Business Acquisition [Line Items]
Payments to acquire businesses, gross			$ 0	$ 811,207
Bankruptcy Auction
Business Acquisition [Line Items]
Area of property acquired (in acres) | a	85
Number of acres with drilling rights (in acres) | a	44
Production of well (in Mcfe) | Mcfe	110
Number of wells acquired | well	174
Number of producing wells acquired | well	120
Number of miles of pipeline acquired | mi	20
2017 Acquisitions
Business Acquisition [Line Items]
Payments to acquire businesses, gross				736,000
Assumed liabilities				11,900
2016 Acquisitions
Business Acquisition [Line Items]
Payments to acquire businesses, gross				75,200
Adjustment to PP&E				$ 2,200
Marion, Monongalia, and Wetzel Counties
Business Acquisition [Line Items]
Area of property acquired (in acres) | a		14