Supplementary Information on Oil and Gas Operations—Unaudited - Average Price and Text (Details) Mcfe in Thousands, MMcf in Thousands, MBbls in Thousands	12 Months Ended
	Dec. 31, 2017 Mcfe Wells $ / mcf $ / Mcfe $ / bbl MBbls MMcf	Dec. 31, 2016 Mcfe Wells $ / mcf $ / Mcfe $ / bbl MBbls MMcf	Dec. 31, 2015 Mcfe Wells $ / mcf $ / Mcfe $ / bbl MBbls MMcf
Reserve Quantities [Line Items]
Company drilling success rate	100.00%	100.00%	95.00%
Gross wells drilled | Wells	8	5	56
Oklahoma
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, increases (decreases)		17,173,000
Texas
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, increases (decreases)		44,452,000
Oil
Reserve Quantities [Line Items]
Number of Bcfe additions | MBbls	777	0	163
Consolidated oil and gas production costs per unit of production | $ / bbl	52.49	40.85	50.29
Mcfe of natural gas liquids
Reserve Quantities [Line Items]
Extensions, discoveries and other additions of Bcfe	4,565	0	16,078
Consolidated oil and gas production costs per unit of production | $ / Mcfe	3.23	2.40	2.24
Oil and Natural Gas Reserves
Reserve Quantities [Line Items]
Increase in proved developed and undeveloped reserves	35.00%	(35.12449%)	(55.17909%)
Extensions, discoveries and other additions of Bcfe	73,931	1,485	62,702
Natural Gas
Reserve Quantities [Line Items]
Number of Bcfe additions | MMcf	64,704	1,485	45,645
Consolidated oil and gas production costs per unit of production | $ / mcf	3.03	1.82	2.41