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, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Roll-forward of Level 3 Assets
Fair Value, net assets, beginning of period	$ 3,904		$ 28,600		$ 13,669		$ 22,107
Fair Value, net assets, end of period	732		15,538		732		15,538
Changes in unrealized gains (losses) relating to assets (liabilities) still held as of period end, included in statement of operations line item;	(3,338)		(8,182)		(5,358)		2,576
Commodity Price Risk Management (loss), net
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	(3,111)		(9,055)		(3,008)		6,098
Settlements included in statement of operations line items:	(66)		(3,900)		(5,545)		(12,357)
Changes in unrealized gains (losses) relating to assets (liabilities) still held as of period end, included in statement of operations line item;	(3,333)		(8,169)		(5,362)		2,577
Sales From Natural Gas Marketing
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	11		(4)		16		35
Settlements included in statement of operations line items:	(6)		(10)		(34)		(105)
Changes in unrealized gains (losses) relating to assets (liabilities) still held as of period end, included in statement of operations line item;	(5)		(13)		4		(1)
Accounts Payable Affiliates
Roll-forward of Level 3 Assets
Changes in fair value Included in blance sheet line item:	0	[1]	(93)	[1]	0	[1]	(240)	[1]
Income (loss) from Discontinued Operations, Net of Tax
Roll-forward of Level 3 Assets
Settlements included in statement of operations line items:	$ 0		$ 0		$ (4,366)		$ 0

[1] Represents the change in fair value related to derivative instruments entered into by us and designated to our affiliated partnerships.