Note 7 - Supplemental Information Relating to Oil and Gas Producing Activities (Unaudited) - Standardized Measure of Discounted Future Net Cash Flows (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Future cash inflows from sales of oil and gas	$ 45,488	$ 67,050
Future production and development costs	(26,931)	(36,575)
Future asset retirement obligations, net of salvage	(15,828)	(15,871)
Future income tax expense	(170)	(321)
Future net cash flows	2,559	14,283
Effect of discounting future net cash flows at 10% per annum	(5,061)	(9,839)
Standardized measure of discounted future net cash flows	$ (2,502)	$ 4,444	$ (5,054)