Note 7 - 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, 2019	Dec. 31, 2018
Balance, beginning of year	$ 4,444	$ (5,054)
Extensions, discoveries and other additions	551
Revision of quantity estimates	(1,650)	8,543
Sales of crude oil and natural gas, net of production costs	(4,686)	(6,290)
Net change in income taxes	88	(112)
Net changes in prices and production costs	(5,161)	4,096
Accretion of discount	444	(505)
Other	3,468	3,766
Balance, end of year	$ (2,502)	$ 4,444