Note 2 - Revenue From Contracts With Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Oil Revenues [Member]
Revenue	$ 31,228	$ 37,039	$ 97,355	$ 100,505
Gas Revenues [Member]
Revenue	226	1,897	2,107	5,882
Natural Gas Liquids Revenues [Member]
Revenue	61	2,677	1,382	6,735
Permian / Delaware Basin [Member] | Oil Revenues [Member]
Revenue	14,315	11,433	38,940	35,471
Permian / Delaware Basin [Member] | Gas Revenues [Member]
Revenue	66	681	377	2,209
Permian / Delaware Basin [Member] | Natural Gas Liquids Revenues [Member]
Revenue	80	890	421	2,301
Rocky Mountain [Member] | Oil Revenues [Member]
Revenue	16,157	23,743	55,524	58,462
Rocky Mountain [Member] | Gas Revenues [Member]
Revenue	14	939	1,176	2,740
Rocky Mountain [Member] | Natural Gas Liquids Revenues [Member]
Revenue	(19)	1,741	958	4,324
South Texas [Member] | Oil Revenues [Member]
Revenue	756	1,863	2,891	6,572
South Texas [Member] | Gas Revenues [Member]
Revenue	146	277	554	933
South Texas [Member] | Natural Gas Liquids Revenues [Member]
Revenue		$ 46	$ 3	$ 110