Reconciliation of Level 3 Fair Value Measurements (Details) (Derivative Financial Instrument Net Assets, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Roll-forward of Level 3 Assets
Fair Value, net assets, beginning of period	$ 62,356	$ 1,111
Fair Value, net assets, end of period	74,817	(129)
Net change in fair value of unsettled derivatives included in statement of operations line item	14,494	(1,478)
Commodity Price Risk Management (loss), net
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	15,189	(1,343)
Settlements included in statement of operations line items:	(2,725)	119
Net change in fair value of unsettled derivatives included in statement of operations line item	14,494	(1,473)
Sales From Natural Gas Marketing
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	1	(22)
Settlements included in statement of operations line items:	(4)	6
Net change in fair value of unsettled derivatives included in statement of operations line item	$ 0	$ (5)