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	6 Months Ended
	Jun. 30, 2018 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)	32 months
Proved Developed Reserves (Energy) | Bcfe	34.8
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)	0.3
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	28.5
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)	0.8