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, 2017 MBoe bbl Mcf	Dec. 31, 2016 MBoe bbl Mcf		Dec. 31, 2015 MBoe bbl Mcf
Proved developed and undeveloped reserves:
Beginning of year (MBoe) | MBoe	117,774	135,233		179,023
Revision of previous estimate (MBoe) | MBoe	11,444	(8,300)	[1]	(36,573)	[1]
Extension and discovery (MBoe) | MBoe	14,975	5,690		6,651
Infill reserves in existing proved fields (MBoe) | MBoe	16,123	7,504		6,304
Purchase of mineral in place (MBoe) | MBoe	5,768	262		0
Production (MBoe) | MBoe	(15,996)	(17,277)		(19,981)
Sales (MBoe) | MBoe	(314)	(5,338)		(191)
End of year (MBoe) | MBoe	149,774	117,774		135,233
Proved developed reserves:
Beginning of year (MBoe) | MBoe	99,079	115,296		136,790
End of year (MBoe) | MBoe	112,961	99,079		115,296
Proved undeveloped reserves
Beginning of year (MBoe) | MBoe	18,695	19,937		42,233
End of year (MBoe) | MBoe	36,813	18,695		19,937
Oil (bbls)
Proved developed and undeveloped reserves:
Beginning of year	15,696	16,735		22,667
Revision of previous estimates	730	(549)	[1]	(3,954)	[1]
Extensions and discoveries	2,235	1,816		1,208
Infill reserves in existing proved fields	1,632	663		670
Purchases of minerals in place	2,019	114		0
Production	(2,715)	(2,974)		(3,783)
Sales	(84)	(109)		(73)
End of year	19,513	15,696		16,735
Proved developed reserves:
Beginning of year	12,724	14,679		17,448
End of year	14,862	12,724		14,679
Proved undeveloped reserves
Beginning of year	2,972	2,056		5,219
End of year	4,651	2,972		2,056
Natural Gas Liquids (bbls)
Proved developed and undeveloped reserves:
Beginning of year	34,482	37,687		48,529
Revision of previous estimates	4,325	(2,473)	[1]	(9,367)	[1]
Extensions and discoveries	4,520	1,588		1,948
Infill reserves in existing proved fields	5,779	2,724		1,861
Purchases of minerals in place	1,197	43		0
Production	(4,737)	(5,014)		(5,274)
Sales	(80)	(73)		(10)
End of year	45,486	34,482		37,687
Proved developed reserves:
Beginning of year	28,502	31,218		35,850
End of year	33,358	28,502		31,218
Proved undeveloped reserves
Beginning of year	5,980	6,469		12,679
End of year	12,128	5,980		6,469
Natural gas (Mcf)
Proved developed and undeveloped reserves:
Beginning of year | Mcf	405,579	484,868		646,961
Revision of previous estimates | Mcf	38,330	(31,670)	[1]	(139,514)	[1]
Extensions and discoveries | Mcf	49,321	13,720		20,974
Infill reserves in existing proved fields | Mcf	52,270	24,704		22,641
Purchases of minerals in place | Mcf	15,313	630		0
Production | Mcf	(51,260)	(55,735)		(65,546)
Sales | Mcf	(903)	(30,938)		(648)
End of year | Mcf	508,650	405,579		484,868
Proved developed reserves:
Beginning of year | Mcf	347,121	416,395		500,950
End of year | Mcf	388,446	347,121		416,395
Proved undeveloped reserves
Beginning of year | Mcf	58,458	68,473		146,011
End of year | Mcf	120,204	58,458		68,473

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