Organization and Summary of Significant Accounting Policies - Concentrations (Details) - Oil and Gas Revenue - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Superior Natural Gas
Concentration Risk [Line Items]
Net oil and gas revenues (percent)	26.00%	29.00%	14.00%
Shell Trading Company
Concentration Risk [Line Items]
Net oil and gas revenues (percent)	21.00%	24.00%	23.00%
Texla Energy Management
Concentration Risk [Line Items]
Net oil and gas revenues (percent)	16.00%
Harvest Pipeline Company
Concentration Risk [Line Items]
Net oil and gas revenues (percent)	12.00%
Laclede Energy Resources
Concentration Risk [Line Items]
Net oil and gas revenues (percent)			17.00%
BG Group
Concentration Risk [Line Items]
Net oil and gas revenues (percent)			10.00%