Sales/Exchange of Assets (Details) a in Thousands, $ in Thousands		1 Months Ended	12 Months Ended
	Dec. 28, 2016 USD ($)	Jun. 30, 2014 USD ($) a well	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Equity Method Investments [Line Items]
Pre-tax gain recorded			$ 8,025	$ 0	$ 34,146
Pre-tax gain on de-designation of derivative instruments		$ 28,000
Nora Gathering, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage		50.00%
Non-core Marcellus Gathering System
Schedule of Equity Method Investments [Line Items]
Pre-tax gain recorded	$ 8,000
Proceeds from sale of oil and gas property and equipment	$ 75,000
Range Resources Corporation
Schedule of Equity Method Investments [Line Items]
Approximate area of acquisition (in acres) | a		73
Number of producing wells acquired | well		900
Area of property transferred under asset exchange agreement (in acres) | a		138
Number of producing wells transferred under asset exchange agreement | well		2,000
Ownership interest transferred		50.00%
Fair value of assets		$ 516,500
Pre-tax gain recorded		34,100
Range Resources Corporation | Acreage
Schedule of Equity Method Investments [Line Items]
Fair value of assets		318,300
Range Resources Corporation | Wells
Schedule of Equity Method Investments [Line Items]
Fair value of assets		198,200
Range Resources Corporation | EQT Production
Schedule of Equity Method Investments [Line Items]
Amount of cash, subject to certain post-closing adjustments		$ 167,300