Derivative Financial Instruments Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement gain (loss)	$ (147,028)	$ (161,229)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(14,228)	(154,167)
NYMEX Oil Contracts [Member]
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement gain (loss)	(99,992)	(106,214)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(10,432)	(73,860)
Gas Contracts [Member]
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement gain (loss)	(41,053)	(34,232)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(24,023)	(82,339)
NGL Contracts [Member]
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement gain (loss)	(5,983)	(20,783)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 20,227	$ 2,032