Derivatives (Effect Of Derivative Instruments Recognized In Statement Of Operations, Derivative Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2016		Jun. 30, 2015		Jun. 30, 2016		Jun. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	$ (22,672)		$ (1,919)		$ (11,743)		$ 4,667
Commodity Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	(22,672)		(1,919)		(11,743)		4,667
Amount of gain settled during the period	5,100		10,100		12,200		21,100
Gain (loss) on derivatives [Member] | Commodity Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	$ (22,672)	[1]	$ (1,919)	[1]	$ (11,743)	[2]	$ 4,667	[2]

[1] Amounts settled during the 2016 and 2015 periods include gains of $5.1 million and $10.1 million, respectively.

[2] Amounts settled during the 2016 and 2015 periods include gains of $12.2 million and $21.1 million, respectively.