Reconciliation of Level 3 Fair Value Measurements (Details) - Derivative Financial Instrument Net Assets - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Roll-forward of Level 3 Assets
Fair Value, net assets, beginning of period	$ 27,285	$ 58,256	$ 91,288	$ 62,356
Fair Value, net assets, end of period	15,932	83,862	15,932	83,862
Commodity Price Risk Management (loss), net
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	4,234	38,085	(16,023)	42,525
Settlements included in statement of operations line items:	(15,587)	(12,530)	(59,243)	(21,063)
Net change in fair value of unsettled derivatives included in statement of operations line item	(2,240)	34,564	(8,273)	31,794
Sales From Natural Gas Marketing
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	0	51	(20)	51
Settlements included in statement of operations line items:	$ 0	$ 0	$ (70)	$ (7)