Derivatives (Effect Of Derivative Instruments Recognized In Statement Of Operations, Derivative Instruments) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gain on derivatives		$ 14,731	$ 10,929
Commodity Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain on derivatives		14,731	10,929
Amount of gain (loss) settled during the period		(1,200)	7,100
Gain on derivatives [Member] | Commodity Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain on derivatives	[1]	$ 14,731	$ 10,929

[1] Amounts settled during the 2017 and 2016 periods include a loss of $1.2 million and a gain of $7.1 million, respectively.