Reconciliation of Level 3 Fair Value Measurements (Details) (Derivative Financial Instrument Net Assets, USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Roll-forward of Level 3 Assets
Fair Value, net assets, beginning of period	$ (6,967)	$ 3,719	$ 1,111	$ 13,610
Fair Value, net assets, end of period	5,932	416	5,932	416
Net change in fair value of unsettled derivatives included in statement of operations line item	11,832	(3,301)	671	(5,447)
Commodity Price Risk Management (loss), net
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	12,758	(3,242)	3,961	(3,265)
Settlements included in statement of operations line items:	142	(66)	882	(5,545)
Net change in fair value of unsettled derivatives included in statement of operations line item	11,831	(3,296)	673	(5,451)
Sales From Natural Gas Marketing
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	2	10	(24)	16
Settlements included in statement of operations line items:	(3)	(5)	2	(34)
Net change in fair value of unsettled derivatives included in statement of operations line item	1	(5)	(2)	4
Income (loss) from Discontinued Operations, Net of Tax
Roll-forward of Level 3 Assets
Settlements included in statement of operations line items:	$ 0	$ 0	$ 0	$ (4,366)