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, 2018 MBoe bbl Mcf	Dec. 31, 2017 MBoe bbl Mcf		Dec. 31, 2016 MBoe Mcf bbl
Proved developed and undeveloped reserves:
Beginning of year (MBoe) | MBoe	149,774	117,774		135,233
Revision of previous estimate (MBoe) | MBoe	(4,165)	11,444	[1]	(8,300)	[1]
Extension and discovery (MBoe) | MBoe	21,033	14,975		5,690
Infill reserves in existing proved fields (MBoe) | MBoe	8,656	16,123		7,504
Purchase of mineral in place (MBoe) | MBoe	2,707	5,768		262
Production (MBoe) | MBoe	(17,070)	(15,996)		(17,277)
Sales (MBoe) | MBoe	(1,254)	(314)		(5,338)
End of year (MBoe) | MBoe	159,681	149,774		117,774
Proved developed reserves:
Beginning of year (MBoe) | MBoe	112,961	99,079		115,296
End of year (MBoe) | MBoe	111,576	112,961		99,079
Proved undeveloped reserves
Beginning of year (MBoe) | MBoe	36,813	18,695		19,937
End of year (MBoe) | MBoe	48,105	36,813		18,695
Oil (bbls)
Proved developed and undeveloped reserves:
Beginning of year	19,513	15,696		16,735
Revision of previous estimates	180	730	[1]	(549)	[1]
Extensions and discoveries	3,250	2,235		1,816
Infill reserves in existing proved fields	1,898	1,632		663
Purchases of minerals in place	701	2,019		114
Production	(2,874)	(2,715)		(2,974)
Sales	(110)	(84)		(109)
End of year	22,558	19,513		15,696
Proved developed reserves:
Beginning of year	14,862	12,724		14,679
End of year	15,192	14,862		12,724
Proved undeveloped reserves
Beginning of year	4,651	2,972		2,056
End of year	7,366	4,651		2,972
Natural Gas Liquids (bbls)
Proved developed and undeveloped reserves:
Beginning of year	45,486	34,482		37,687
Revision of previous estimates	(1,368)	4,325	[1]	(2,473)	[1]
Extensions and discoveries	5,149	4,520		1,588
Infill reserves in existing proved fields	2,795	5,779		2,724
Purchases of minerals in place	856	1,197		43
Production	(4,925)	(4,737)		(5,014)
Sales	(197)	(80)		(73)
End of year	47,796	45,486		34,482
Proved developed reserves:
Beginning of year	33,358	28,502		31,218
End of year	33,515	33,358		28,502
Proved undeveloped reserves
Beginning of year	12,128	5,980		6,469
End of year	14,281	12,128		5,980
Natural gas (Mcf)
Proved developed and undeveloped reserves:
Beginning of year | Mcf	508,650	405,579		484,868
Revision of previous estimates | Mcf	(17,859)	38,330	[1]	(31,670)	[1]
Extensions and discoveries | Mcf	75,806	49,321		13,720
Infill reserves in existing proved fields | Mcf	23,778	52,270		24,704
Purchases of minerals in place | Mcf	6,897	15,313		630
Production | Mcf	(55,627)	(51,260)		(55,735)
Sales | Mcf	(5,682)	(903)		(30,938)
End of year | Mcf	535,963	508,650		405,579
Proved developed reserves:
Beginning of year | Mcf	388,446	347,121		416,395
End of year | Mcf	377,216	388,446		347,121
Proved undeveloped reserves
Beginning of year | Mcf	120,204	58,458		68,473
End of year | Mcf	158,747	120,204		58,458

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