Reconciliation of Level 3 Fair Value Measurements (Details) (Derivative Financial Instrument Net Assets [Domain], USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011
Fair Value, Net Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, net assets, beginning of period	$ 22,107		$ 10,762
Fair Value, net assets, end of period	28,600		5,790
Changes in unrealized gains (losses) relating to assets (liabilities) still held as of period end, included in statement of operations line item;	8,662		(1,814)
Commodity Price Risk Management, net [Member]
Fair Value, Net Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Changes in fair value included in statement of operations line item:	15,153		(2,108)
Settlements included in statement of operations line items:	(8,458)		(2,210)
Changes in unrealized gains (losses) relating to assets (liabilities) still held as of period end, included in statement of operations line item;	8,661		(1,809)
Sales From Natural Gas Marketing [Member]
Fair Value, Net Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Changes in fair value included in statement of operations line item:	39		20
Settlements included in statement of operations line items:	(95)		(86)
Changes in unrealized gains (losses) relating to assets (liabilities) still held as of period end, included in statement of operations line item;	1		(5)
Accounts Payable Affiliates [Member]
Fair Value, Net Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Changes in Fair Value Included in Balance Sheet Line Item	(146)	[1]	(637)	[1]
Accounts Receivable Affiliates [Member]
Fair Value, Net Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Changes in Fair Value Included in Balance Sheet Line Item	$ 0	[1]	$ 49	[1]

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