Supplemental Oil And Gas Information (Schedule Of Reserve Value By Category And The Respective Present Values, Before Income Taxes, Discounted At 10% As A Percentage Of Total Proved Reserves) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reserve Quantities [Line Items]
Total proved reserves year-end reserve report	$ 8,170	$ 5,815	$ 8,287
Proved developed producing reserves (PDP)	$ 7,065	$ 5,397	$ 7,686
% of PDP reserves to total proved reserves	87.00%	93.00%	93.00%
Proved developed non-producing reserves	$ 1,082	$ 418	$ 601
% of PDNP reserves to total proved reserves	13.00%	7.00%	7.00%
Proved undeveloped reserves (PUD)	$ 23
Oil [Member]
Reserve Quantities [Line Items]
Total proved reserves year-end reserve report	8,170	$ 5,815	$ 8,287
Proved developed producing reserves (PDP)	$ 7,065	$ 5,397	$ 7,686
% of PDP reserves to total proved reserves	87.00%	93.00%	93.00%
Proved developed non-producing reserves	$ 1,082	$ 418	$ 601
% of PDNP reserves to total proved reserves	13.00%	7.00%	7.00%
Proved undeveloped reserves (PUD)	$ 23

Supplemental Oil And Gas Information (Schedule Of Reserve Value By Category And The Respective Present Values, Before Income Taxes, Discounted At 10% As A Percentage Of Total Proved Reserves) (Details) - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Reserve Quantities [Line Items]

Total proved reserves year-end reserve report

$ 8,170

$ 5,815

$ 8,287

Proved developed producing reserves (PDP)

$ 7,065

$ 5,397