Note 3 - Revenue From Contracts With Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Oil Revenues [Member]
Revenues	$ 27,472	$ 11,313	$ 63,466	$ 26,814
Gas Revenues [Member]
Revenues	1,608	1,063	3,985	3,045
Natural Gas Liquids Revenues [Member]
Revenues	1,835	760	4,058	2,064
Permian / Delaware Basin [Member] | Oil Revenues [Member]
Revenues	9,664	1,662	24,039	4,149
Permian / Delaware Basin [Member] | Gas Revenues [Member]
Revenues	609	571	1,528	1,327
Permian / Delaware Basin [Member] | Natural Gas Liquids Revenues [Member]
Revenues	613	312	1,411	701
Rocky Mountain [Member] | Oil Revenues [Member]
Revenues	15,479	8,244	34,719	19,641
Rocky Mountain [Member] | Gas Revenues [Member]
Revenues	674	429	1,802	1,300
Rocky Mountain [Member] | Natural Gas Liquids Revenues [Member]
Revenues	1,180	421	2,583	1,316
South Texas [Member] | Oil Revenues [Member]
Revenues	2,329	1,407	4,708	3,024
South Texas [Member] | Gas Revenues [Member]
Revenues	325	63	655	418
South Texas [Member] | Natural Gas Liquids Revenues [Member]
Revenues	$ 42	$ 27	$ 64	$ 47