Derivatives (Effect Of Derivative Instruments Recognized In Statement Of Operations, Derivative Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2017		Jun. 30, 2016		Jun. 30, 2017		Jun. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	$ 8,902		$ (22,672)		$ 23,633		$ (11,743)
Commodity Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	8,902		(22,672)		23,633		(11,743)
Amount of gain (loss) settled during the period	(400)		5,100		(1,600)		12,200
Gain (loss) on derivatives [Member] | Commodity Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	$ 8,902	[1]	$ (22,672)	[1]	$ 23,633	[2]	$ (11,743)	[1]

[1] Amounts settled during the 2017 and 2016 periods include a loss of $0.4 million and a gain of $5.1 million, respectively.

[2] Amounts settled during the 2017 and 2016 periods include a loss of $1.6 million and a gain of $12.2 million, respectively.