Derivative Financial Instruments Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement (gain) loss	$ (7)	$ (147,028)
Gain (Loss) on Derivative Instruments, Net, Pretax	114,774	14,228
NYMEX Oil Contracts [Member]
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement (gain) loss	9,084	(99,992)
Gain (Loss) on Derivative Instruments, Net, Pretax	49,590	10,432
Gas Contracts [Member]
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement (gain) loss	(17,506)	(41,053)
Gain (Loss) on Derivative Instruments, Net, Pretax	44,468	24,023
NGL Contracts [Member]
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement (gain) loss	8,415	(5,983)
Gain (Loss) on Derivative Instruments, Net, Pretax	$ 20,716	$ (20,227)