Derivative Financial Instruments (Schedule Of Open Oil Derivative Positions) (Details)	12 Months Ended
	Dec. 31, 2017 $ / bbl bbl
NYMEX West Texas Intermediate Price Swaps Oil Q1-Q4 2018 [Member]
Derivative [Line Items]
Volume Per Day (Bbls/d) | bbl	49,625
Weighted Average Price Swap	52.13
NYMEX West Texas Intermediate Price Swaps Oil Q1-Q4 2019 [Member]
Derivative [Line Items]
Volume Per Day (Bbls/d) | bbl	7,307
Weighted Average Price Swap	52.22
NYMEX West Texas Intermediate Price Collars Oil Q1-Q4 2018 [Member]
Derivative [Line Items]
Volume Per Day (Bbls/d) | bbl	51,860
Weighted Average Floor Price	46.06
Weighted Average Ceiling Price	56.06
NYMEX West Texas Intermediate Price Collars Oil Q1-Q4 2019 [Member]
Derivative [Line Items]
Volume Per Day (Bbls/d) | bbl	6,559
Weighted Average Floor Price	45.82
Weighted Average Ceiling Price	55.82
Midland Sweet Basis Swaps Oil Q1-Q4 2018 [Member]
Derivative [Line Items]
Volume Per Day (Bbls/d) | bbl	23,000
Weighted Average Differential To WTI	(1.02)
Argus LLS Basis Swaps Oil Q1-Q4 2018 [Member]
Derivative [Line Items]
Volume Per Day (Bbls/d) | bbl	12,000
Weighted Average Differential To WTI	3.95
Western Canadian Select Basis Swaps Oil Q1-Q4 2018 [Member]
Derivative [Line Items]
Volume Per Day (Bbls/d) | bbl	75,490
Weighted Average Differential To WTI	(14.84)
Midland Sweet Basis Swaps Oil Q1-Q4 2019 [Member]
Derivative [Line Items]
Volume Per Day (Bbls/d) | bbl	27,000
Weighted Average Differential To WTI	(0.47)
Western Canadian Select Basis Collars Oil Q1-Q4 2018 [Member]
Derivative [Line Items]
Volume Per Day (Bbls/d) | bbl	1,830
Weighted Average Floor Differential to WTI	(15.50)
Weighted Average Ceiling Differential to WTI	(13.93)