Derivatives (Effect Of Derivative Instruments Recognized In Statement Of Operations, Not Designated As Hedging Instruments) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives		$ 14,732	$ (22,813)
Cash receipts on derivatives settled		173	9,658
Commodity Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives	[1]	$ 14,732	$ (22,813)

[1] Amount settled during the period are gains of $173 and $9,658, respectively.