Note 2 - Revenue From Contracts With Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Oil Revenues [Member]
Revenue	$ 15,535	$ 31,981
Gas Revenues [Member]
Revenue	86	1,473
Natural Gas Liquids Revenues [Member]
Revenue	97	1,056
Permian / Delaware Basin [Member] | Oil Revenues [Member]
Revenue	8,507	9,063
Permian / Delaware Basin [Member] | Gas Revenues [Member]
Revenue	14	287
Permian / Delaware Basin [Member] | Natural Gas Liquids Revenues [Member]
Revenue	(2)	313
Rocky Mountain [Member] | Oil Revenues [Member]
Revenue	7,028	21,800
Rocky Mountain [Member] | Gas Revenues [Member]
Revenue	72	954
Rocky Mountain [Member] | Natural Gas Liquids Revenues [Member]
Revenue	99	740
South Texas [Member] | Oil Revenues [Member]
Revenue		1,118
South Texas [Member] | Gas Revenues [Member]
Revenue		232
South Texas [Member] | Natural Gas Liquids Revenues [Member]
Revenue		$ 3