Derivative Financial Instruments (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative contracts not designated as hedging instruments
Fair value of derivative instruments - current assets		$ 8,698,000	$ 4,345,000
Fair value of derivative instruments - long-term assets		16,092,000	417,000
Total derivative assets		24,790,000	4,762,000	24,631,000
Fair value of derivative instruments - current liabilities		(90,551,000)	(65,489,000)
Fair value of derivative liabilities - long-term liabilities		(65,403,000)	(66,290,000)
Total derivative liabilities		(155,954,000)	(131,779,000)
Financial Statement Impact of Derivative Contracts
Unrealized gain (loss)			190,000	336,000
Total Revenue: derivative gain (loss)		(29,035,000)	(53,932,000)	(120,352,000)
Total derivative loss related to purchased product costs		(52,960,000)	(27,713,000)	(68,883,000)
Derivative gain related to facility expenses		6,480,000	1,295,000	373,000
Derivative gain related to interest expense			1,871,000	2,509,000
Total loss		(75,515,000)	(78,289,000)	(186,017,000)
Premium payments, net of amortization		0	4,400,000
Producer's option to extend successive years, number		5
Embedded derivative in natural gas processing and purchase contract
Financial Statement Impact of Derivative Contracts
Notional amount for embedded derivative in commodity contract (in Dth per day)		9,000
Estimated fair value of embedded derivative contract liability including portion allocable to host processing agreement		114,928,000
Inception value for period from April 1, 2015 to December 31, 2022		(53,507,000)
Recorded value of embedded derivative contract liability		61,421,000
Embedded derivative in electricity purchase contract
Financial Statement Impact of Derivative Contracts
Estimated fair value of embedded derivative contract asset		7,500,000	1,000,000
Derivative instruments not designated as hedging instruments
Derivative contracts not designated as hedging instruments
Fair value of derivative instruments - current assets		8,698,000	4,345,000
Fair value of derivative instruments - long-term assets		16,092,000	417,000
Total derivative assets		24,790,000	4,762,000
Fair value of derivative instruments - current liabilities		(90,551,000)	(65,489,000)
Fair value of derivative liabilities - long-term liabilities		(65,403,000)	(66,290,000)
Total derivative liabilities		(155,954,000)	(131,779,000)
Financial Statement Impact of Derivative Contracts
Notional quantity of crude oil contract (in bbl)		8,244,902
Notional quantity of natural gas contract (in MMBtu)		16,021,887
Natural Gas Liquids (gal)		86,563,841
Derivative instruments not designated as hedging instruments | Derivative revenue
Financial Statement Impact of Derivative Contracts
Realized (loss) gain		(48,093,000)	(33,560,000)	87,289,000
Unrealized gain (loss)		19,058,000	(20,372,000)	(207,641,000)
Total Revenue: derivative gain (loss)		(29,035,000)	(53,932,000)	(120,352,000)
Amortization of premium payments		4,400,000	3,300,000	5,700,000
Realized gain (loss) on early settlement	15,200,000
Realized gains on early settlement recorded in Realized (loss) gain - revenue	26,500,000
Realized gains on early settlement recorded in derivative loss related to purchased product cost	11,300,000
Derivative instruments not designated as hedging instruments | Derivative related to purchased product costs
Financial Statement Impact of Derivative Contracts
Realized (loss) gain		(27,711,000)	(21,909,000)	(53,052,000)
Unrealized gain (loss)		(25,249,000)	(5,804,000)	(15,831,000)
Total derivative loss related to purchased product costs		(52,960,000)	(27,713,000)	(68,883,000)
Derivative instruments not designated as hedging instruments | Derivative related to facility expenses
Financial Statement Impact of Derivative Contracts
Unrealized gain (loss)		6,480,000	1,295,000	373,000
Derivative instruments not designated as hedging instruments | Derivative related to interest expense
Financial Statement Impact of Derivative Contracts
Realized (loss) gain			2,380,000	2,000,000
Unrealized gain (loss)			(509,000)	509,000
Derivative gain related to interest expense			1,871,000	2,509,000
Derivative instruments not designated as hedging instruments | Miscellaneous income, net
Financial Statement Impact of Derivative Contracts
Unrealized gain			$ 190,000	$ 336,000