Supplemental Oil And Gas Information (Schedule Of Standardized Measure Of Discounted Futures Net Cash Flows From Proved Oil And Gas Reserves) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Oil And Gas Information [Abstract]
Future cash inflows	$ 18,036	$ 40,655	$ 65,871
Future production costs and taxes	(12,664)	(24,829)	(35,877)
Future development costs	(538)	(542)	(2,833)
Future income tax expenses
Future net cash flows	4,834	15,284	27,161
Discount at 10% for timing of cash flows	(1,937)	(6,919)	(13,185)
Standardized measure of discounted future net cash flows	$ 2,897	$ 8,365	$ 13,976	$ 8,170