Derivatives (Effect Of Derivative Instruments Recognized In Statement Of Operations, Derivative Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2016		Sep. 30, 2015		Sep. 30, 2016		Sep. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	$ 6,969		$ 8,250		$ (4,774)		$ 12,917
Commodity Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	6,969		8,250		(4,774)		12,917
Amount of gain settled during the period	(500)		11,100		11,700		32,200
Gain (loss) on derivatives [Member] | Commodity Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	$ 6,969	[1]	$ 8,250	[1]	$ (4,774)	[2]	$ 12,917	[2]

[1] Amounts settled during the 2016 and 2015 periods include a loss of $0.5 million and a gain of $11.1 million, respectively.

[2] Amounts settled during the 2016 and 2015 periods include gains of $11.7 million and $32.2 million, respectively.