Organization and Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue receivable	$ 6,364				$ 15,340				$ 6,364	$ 15,340
Revenues	19,789	$ 20,886	$ 21,507	$ 24,917	$ 35,080	$ 28,184	$ 24,251	$ 20,772	87,099	108,287	$ 66,667
Total oil sales
Disaggregation of Revenue [Line Items]
Revenue receivable	1,100								1,100
Revenues									21,027	31,258	20,614
Total gas sales
Disaggregation of Revenue [Line Items]
Revenue receivable	4,800								4,800
Revenues									50,768	60,922	37,963
Total ngl sales
Disaggregation of Revenue [Line Items]
Revenue receivable	$ 500								500
Revenues									$ 15,303	$ 16,107	$ 8,090
Minimum
Disaggregation of Revenue [Line Items]
Revenue recognized, period									1 month
Maximum
Disaggregation of Revenue [Line Items]
Revenue recognized, period									2 months