Supplemental Oil And Gas Information (Schedule Of Changes In The Standardized Measure Of Discounted Future Net Cash Flows From Proved Oil And Gas Reserves) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Oil And Gas Information [Abstract]
Balance, beginning of year	$ 8,287	$ 34,531	$ 38,708
Sales, net of production costs and taxes	(2,037)	(1,901)	(8,385)
Discoveries and extensions, net of costs	35	5	4,231
Purchase of reserves in place
Sale of reserves in place	(10)
Net changes in prices and production costs	(863)	(16,009)	(829)
Revisions of quantity estimates	(412)	(22,431)	(6,610)
Previously estimated development cost incurred during the year			508
Changes in future development costs	196	4,890	(1,913)
Changes in timing and other	(20)	(56)	1,312
Accretion of discount	639	3,373	4,247
Net change in income taxes		5,885	3,262
Balance, end of year	$ 5,815	$ 8,287	$ 34,531