Derivative Instruments (Schedule of (Gain) Loss on Derivative Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments, Gain (Loss), Commodity [Line Items]
(Gain) loss on derivatives, net	$ 24,377	$ (11,744)	$ (27,004)	$ 29,938
Gain (Loss) on Embedded Derivative, Net	8,000	0	8,000	0
Crude Oil [Member]
Derivative Instruments, Gain (Loss), Commodity [Line Items]
(Gain) loss on derivatives, net	8,409	(8,309)	(39,754)	12,006
Natural Gas [Member]
Derivative Instruments, Gain (Loss), Commodity [Line Items]
(Gain) loss on derivatives, net	(2,183)	(3,490)	(12,902)	12,167
Deferred Premiums On Derivative Instruments [Member]
Derivative Instruments, Gain (Loss), Commodity [Line Items]
(Gain) loss on derivatives, net	$ 10,151	$ 55	$ 17,652	$ 5,765