Supplemental Oil And Gas Disclosures (Schedule Of Proved Developed And Undeveloped Oil And Gas Reserve Quantities) (Details) bbl in Thousands, Mcf in Thousands, MBoe in Thousands		12 Months Ended
		Dec. 31, 2016 MBoe bbl Mcf	Dec. 31, 2015 MBoe bbl Mcf	Dec. 31, 2014 MBoe bbl Mcf
Proved developed and undeveloped reserves:
Beginning of year (MBoe) | MBoe		135,233	179,023	159,934
Revision of previous estimate (MBoe) | MBoe	[1]	(8,300)	(36,573)	(10,905)
Extension and discovery (MBoe) | MBoe		5,690	6,651	35,101
Infill reserves in existing proved fields (MBoe) | MBoe		7,504	6,304	14,217
Purchase of mineral in place (MBoe) | MBoe		262	0	385
Production (MBoe) | MBoe		(17,277)	(19,981)	(18,282)
Sales (MBoe) | MBoe		(5,338)	(191)	(1,427)
End of year (MBoe) | MBoe		117,774	135,233	179,023
Proved developed reserves:
Beginning of year (MBoe) | MBoe		115,296	136,790	123,403
End of year (MBoe) | MBoe		99,079	115,296	136,790
Proved undeveloped reserves
Beginning of year (MBoe) | MBoe		19,937	42,233	36,531
End of year (MBoe) | MBoe		18,695	19,937	42,233
Oil (bbls)
Proved developed and undeveloped reserves:
Beginning of year		16,735	22,667	21,765
Revision of previous estimates	[1]	(549)	(3,954)	(3,174)
Extensions and discoveries		1,816	1,208	5,327
Infill reserves in existing proved fields		663	670	2,775
Purchases of minerals in place		114	0	236
Production		(2,974)	(3,783)	(3,844)
Sales		(109)	(73)	(418)
End of year		15,696	16,735	22,667
Proved developed reserves:
Beginning of year		14,679	17,448	15,594
End of year		12,724	14,679	17,448
Proved undeveloped reserves
Beginning of year		2,056	5,219	6,171
End of year		2,972	2,056	5,219
Natural Gas Liquids (bbls)
Proved developed and undeveloped reserves:
Beginning of year		37,687	48,529	41,205
Revision of previous estimates	[1]	(2,473)	(9,367)	(2,266)
Extensions and discoveries		1,588	1,948	10,850
Infill reserves in existing proved fields		2,724	1,861	3,577
Purchases of minerals in place		43	0	88
Production		(5,014)	(5,274)	(4,629)
Sales		(73)	(10)	(296)
End of year		34,482	37,687	48,529
Proved developed reserves:
Beginning of year		31,218	35,850	30,437
End of year		28,502	31,218	35,850
Proved undeveloped reserves
Beginning of year		6,469	12,679	10,768
End of year		5,980	6,469	12,679
Natural gas (Mcf)
Proved developed and undeveloped reserves:
Beginning of year | Mcf		484,868	646,961	581,784
Revision of previous estimates | Mcf	[1]	(31,670)	(139,514)	(32,790)
Extensions and discoveries | Mcf		13,720	20,974	113,541
Infill reserves in existing proved fields | Mcf		24,704	22,641	47,189
Purchases of minerals in place | Mcf		630	0	368
Production | Mcf		(55,735)	(65,546)	(58,854)
Sales | Mcf		(30,938)	(648)	(4,277)
End of year | Mcf		405,579	484,868	646,961
Proved developed reserves:
Beginning of year | Mcf		416,395	500,950	464,234
End of year | Mcf		347,121	416,395	500,950
Proved undeveloped reserves
Beginning of year | Mcf		68,473	146,011	117,550
End of year | Mcf		58,458	68,473	146,011

[1] Natural gas revisions of previous estimates decreased primarily due to a decline in natural gas prices.