Fair Value Measurements (Schedule Of Quantitative Information About Unobservable Inputs) (Details) - Level 3 $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / Unit
Crude Oil | Collar
Derivative assets (liabilities), Fair Value | $	$ (77)	[1]
Derivatives assets (liabilities), Valuation Technique(s)	Discounted cash flow	[1]
Unobservable Input	Forward commodity price curve	[1]
Crude Oil | Three-way collar
Derivative assets (liabilities), Fair Value | $	$ (3,473)	[1]
Derivatives assets (liabilities), Valuation Technique(s)	Discounted cash flow	[1]
Unobservable Input	Forward commodity price curve	[1]
Crude Oil | Minimum | Collar
Derivative, Average Forward Price	0.00
Crude Oil | Minimum | Three-way collar
Derivative, Average Forward Price	0.00
Crude Oil | Maximum | Collar
Derivative, Average Forward Price	2.48
Crude Oil | Maximum | Three-way collar
Derivative, Average Forward Price	5.96
Natural gas | Three-way collar
Derivative assets (liabilities), Fair Value | $	$ 3,344	[1]
Derivatives assets (liabilities), Valuation Technique(s)	Discounted cash flow	[1]
Unobservable Input	Forward commodity price curve	[1]
Natural gas | Minimum | Three-way collar
Derivative, Average Forward Price	0.00
Natural gas | Maximum | Three-way collar
Derivative, Average Forward Price	0.68

[1] The commodity contracts detailed in this category include non-exchange-traded crude oil collars and crude 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 received within the settlement period.