Divestitures, Exchanges of Properties, Acquisitions and Joint-Venture Funding (Divestiture) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Gain (Loss) on Disposition of Oil and Gas Property		$ 0	$ 85,493	$ 0
XOM II Exchange [Member]
Business Acquisition [Line Items]
Costs Associated With Sale of Oil and Gas Property and Equipment		3,000
Gain (Loss) on Disposition of Oil and Gas Property		20,000
XOM I Exchange [Member]
Business Acquisition [Line Items]
Costs Associated With Sale of Oil and Gas Property and Equipment		3,000
Gain (Loss) on Disposition of Oil and Gas Property		65,000
Granite Wash Assets Sale [Member]
Business Acquisition [Line Items]
Costs Associated With Sale of Oil and Gas Property and Equipment		10,000
Gain (Loss) on Disposition of Oil and Gas Property		294,000
Proceeds from sale of oil and natural gas property		1,800,000
Permian Basin Assets Sale [Member]
Business Acquisition [Line Items]
Costs Associated With Sale of Oil and Gas Property and Equipment		2,000
Gain (Loss) on Disposition of Oil and Gas Property		(28,000)
Proceeds from sale of oil and natural gas property		352,000
STACK acreage divestiture [Member]
Business Acquisition [Line Items]
Gain (Loss) on Disposition of Oil and Gas Property		36,000
Proceeds from sale of oil and natural gas property		$ 44,000
Howard County [Member]
Business Acquisition [Line Items]
Costs Associated With Sale of Oil and Gas Property and Equipment	$ 1,000
Gain (Loss) on Disposition of Oil and Gas Property	177,000
Proceeds from sale of oil and natural gas property	$ 276,000