Reconciliation of Level 3 Fair Value Measurements (Details) - Derivative Financial Instrument Net Assets - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Roll-forward of Level 3 Assets
Fair Value, net assets, beginning of period	$ 73,105	$ 74,817	$ 91,288	$ 62,356
Fair Value, net assets, end of period	27,285	58,255	27,285	58,255
Commodity Price Risk Management (loss), net
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	(26,422)	(10,749)	(20,257)	4,440
Settlements included in statement of operations line items:	(19,398)	(5,809)	(43,656)	(8,534)
Net change in fair value of unsettled derivatives included in statement of operations line item	(18,210)	(10,056)	(13,105)	3,629
Sales From Natural Gas Marketing
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	0	(1)	(20)	0
Settlements included in statement of operations line items:	$ 0	$ (3)	$ (70)	$ (7)