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, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Oil And Gas Information [Abstract]
Future cash inflows	$ 39,889	$ 27,253	$ 38,566
Future production costs and taxes	(23,343)	(16,270)	(23,500)
Future development costs	(1,586)	(553)	(951)
Future net cash flows	14,960	10,430	14,115
Discount at 10% for timing of cash flows	(6,790)	(4,615)	(5,828)
Standardized measure of discounted future net cash flows	$ 8,170	$ 5,815	$ 8,287	$ 34,531