Derivative Instruments (Schedule of (Gain) Loss on Derivative Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Derivative Instruments, Gain (Loss), Commodity [Line Items]
(Gain) loss on derivatives, net	$ (25,316)	$ (10,553)
Crude Oil [Member]
Derivative Instruments, Gain (Loss), Commodity [Line Items]
(Gain) loss on derivatives, net	(18,480)	(21,891)
Natural Gas [Member]
Derivative Instruments, Gain (Loss), Commodity [Line Items]
(Gain) loss on derivatives, net	$ (6,836)	$ 11,338