Fair Value Measurements (Schedule Of Quantitative Information About Unobservable Inputs) (Details) - Level 3 [Member] - Three-way collar [Member] $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / Unit	[1]
Oil [Member]
Derivative fair value | $	$ (7,607)
Derivatives Valuation Technique(s)	Discounted cash flow
Unobservable Input	Forward commodity price curve
Oil [Member] | Minimum [Member]
Forward commodity price curve	0.00
Oil [Member] | Maximum [Member]
Forward commodity price curve	17.65
Natural Gas [Member]
Derivative fair value | $	$ 88
Derivatives Valuation Technique(s)	Discounted cash flow
Unobservable Input	Forward commodity price curve
Natural Gas [Member] | Minimum [Member]
Forward commodity price curve	0.00
Natural Gas [Member] | Maximum [Member]
Forward commodity price curve	0.12

[1] The commodity contracts detailed in this category include non-exchange-traded crude oil and natural gas three-way collars that are valued based on NYMEX. The forward pricing range represents the low and high price expected to be paid or received within the settlement period.