Oil and Natural Gas Property Transactions - VPP Volume Remaining to Be Delivered Table (Details) - VPP 9 Mid-Continent [Member] MMBbls in Millions, Bcf in Millions, Bcfe in Billions	12 Months Ended
	Dec. 31, 2017 Bcfe MMBbls Bcf	May 31, 2011 Bcfe MMBbls Bcf
VPP Volumes Remaining to be Delivered [Line Items]
Proved Developed Reserves (Energy) | Bcfe		177.0
Reserve Volume Remaining [Member]
VPP Volumes Remaining to be Delivered [Line Items]
Term Remaining (in Months)	38 months
Proved Developed Reserves (Energy) | Bcfe	41.7
Oil [Member]
VPP Volumes Remaining to be Delivered [Line Items]
Proved Developed Reserves (Volume)		1.7
Oil [Member] | Reserve Volume Remaining [Member]
VPP Volumes Remaining to be Delivered [Line Items]
Proved Developed Reserves (Volume)	0.4
Natural Gas [Member]
VPP Volumes Remaining to be Delivered [Line Items]
Proved Developed Reserves (Volume) | Bcf		138,000.0
Natural Gas [Member] | Reserve Volume Remaining [Member]
VPP Volumes Remaining to be Delivered [Line Items]
Proved Developed Reserves (Volume) | Bcf	34.1
NGL [Member]
VPP Volumes Remaining to be Delivered [Line Items]
Proved Developed Reserves (Volume)		4.8
NGL [Member] | Reserve Volume Remaining [Member]
VPP Volumes Remaining to be Delivered [Line Items]
Proved Developed Reserves (Volume)	0.9