Derivative Financial Instruments Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement (gain) loss	$ (13,092)	$ (57,496)	$ (29,402)	$ (306,234)
Net derivative (gain) loss	80,599	(28,037)	(89,364)	121,086
Oil Contracts [Member]
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement (gain) loss	2,472	(49,241)	14,310	(221,397)
Net derivative (gain) loss	45,874	(733)	(41,910)	49,608
Gas Contracts [Member]
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement (gain) loss	(24,088)	(10,096)	(63,345)	(82,588)
Net derivative (gain) loss	(6,068)	(14,006)	(56,574)	24,460
NGL Contracts [Member]
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative settlement (gain) loss	8,524	1,841	19,633	(2,249)
Net derivative (gain) loss	$ 40,793	$ (13,298)	$ 9,120	$ 47,018