Acquisitions (Details) a in Thousands, $ in Thousands				6 Months Ended
	Jun. 30, 2017 USD ($) a	Feb. 27, 2017 USD ($) a Mcfe well mi	Feb. 01, 2017 USD ($) a	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)
Business Acquisition [Line Items]
Payments to acquire businesses, gross				$ 811,207	$ 0
Bankruptcy Auction
Business Acquisition [Line Items]
Area of property acquired (in acres) | a		85
Payments to acquire businesses, gross		$ 522,500
Number of acres with drilling rights (in acres) | a		44
Production of well (in MMcfe) | Mcfe		110
Number of wells acquired | well		174
Number of miles of pipeline acquired | mi		20
Allegheny, Washington, and Westmore Counties
Business Acquisition [Line Items]
Area of property acquired (in acres) | a	11
Payments to acquire businesses, gross	$ 83,500
First Quarter 2017 Acquisitions
Business Acquisition [Line Items]
Payments to acquire businesses, gross				736,000
PP&E acquired	747,900			747,900
Current liabilities assumed	7,200			7,200
Noncurrent liabilities assumed	$ 4,700			4,700
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
Payments to acquire businesses, gross			$ 130,000