Derivative Financial Instruments Gains and Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, (Gain) Loss [Line Items]
Derivative settlement (gain) loss	$ 135,803	$ (21,234)	$ (329,478)
Net derivative (gain) loss	(161,832)	26,414	250,633
Oil Contracts [Member]
Derivative Instruments, (Gain) Loss [Line Items]
Derivative settlement (gain) loss	68,860	31,176	(243,102)
Net derivative (gain) loss	(192,002)	71,502	85,370
Gas Contracts [Member]
Derivative Instruments, (Gain) Loss [Line Items]
Derivative settlement (gain) loss	13,029	(87,857)	(94,936)
Net derivative (gain) loss	35,411	(76,315)	81,060
NGL Contracts [Member]
Derivative Instruments, (Gain) Loss [Line Items]
Derivative settlement (gain) loss	53,914	35,447	8,560
Net derivative (gain) loss	$ (5,241)	$ 31,227	$ 84,203