Note 8 - Supplemental Information Relating to Oil and Gas Producing Activities (Unaudited) - Changes in the Standardized Measure of Discounted Future Net Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Balance, beginning of year	$ (5,054)	$ (9,924)
Extensions, discoveries and other additions		197
Revision of quantity estimates	8,543	4,031
Sales of crude oil and natural gas, net of production costs	(6,290)	(4,926)
Net change in income taxes	(112)	(20)
Net changes in prices and production costs	4,096	2,478
Accretion of discount	(505)	(992)
Other	3,766	4,102
Balance, end of year	$ 4,444	$ (5,054)