Supplemental Oil And Gas Information (Schedule Of Results Of Operations From Oil And Gas Producing Activities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Oil And Gas Information [Abstract]
Revenues	$ 4,113	$ 5,631	$ 13,260
Production costs and taxes	(3,064)	(3,360)	(4,876)
Depreciation, depletion and amortization	(1,009)	(2,538)	(2,766)
Impairment	(2,805)	(14,526)
Income (loss) from oil and gas producing activities	$ (2,765)	$ (14,793)	$ 5,618