Derivative Financial Instruments (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative contracts not designated as hedging instruments
Fair value of derivative instruments - current assets	$ 19,504,000	$ 8,698,000
Fair value of derivative instruments - long-term assets	10,878,000	16,092,000
Total derivative assets	30,382,000	24,790,000	4,762,000
Fair value of derivative instruments - current liabilities	(27,229,000)	(90,551,000)
Fair value of derivative liabilities - long-term liabilities	(32,190,000)	(65,403,000)
Total derivative liabilities	(59,419,000)	(155,954,000)
Financial Statement Impact of Derivative Contracts
Unrealized gain (loss)	102,127,000	(4,147,000)	(28,475,000)
Total revenue: derivative gain (loss)	56,535,000	(29,035,000)	(53,932,000)
Total derivative gain (loss) related to purchase product costs	13,962,000	(52,960,000)	(27,713,000)
Derivative (loss) gain related to facility expenses	(1,371,000)	6,480,000	1,295,000
Derivative gain related to interest expense			1,871,000
Total gain (loss)	69,126,000	(75,515,000)	(78,289,000)
Gain (Loss) on Early Settlement of Commodity Contracts	15,100,000
Embedded derivative in natural gas processing and purchase contract
Derivative financial instruments
Notional amount for embedded derivative in commodity contract (in Dth per day)	9,000
Producer's option to extend successive years, number	5 years
Estimated fair value of embedded derivative contract liability including portion allocable to host processing agreement	93,610,000
Inception value for period from April 1, 2015 to December 31, 2022	(53,507,000)
Recorded value of embedded derivative contract liability	40,103,000
Embedded derivative in electricity purchase contract
Derivative financial instruments
Estimated fair value of embedded derivative contract asset	6,100,000	7,500,000
Derivative instruments not designated as hedging instruments
Derivative financial instruments
Notional quantity of crude oil contract (in bbl)	3,470,375
Notional quantity of natural gas contract (in MMBtu)	5,655,676
Natural Gas Liquids (gal)	78,012,934
Derivative contracts not designated as hedging instruments
Fair value of derivative instruments - current assets	19,504,000	8,698,000
Fair value of derivative instruments - long-term assets	10,878,000	16,092,000
Total derivative assets	30,382,000	24,790,000
Fair value of derivative instruments - current liabilities	(27,229,000)	(90,551,000)
Fair value of derivative liabilities - long-term liabilities	(32,190,000)	(65,403,000)
Total derivative liabilities	(59,419,000)	(155,954,000)
Derivative instruments not designated as hedging instruments | Derivative revenue
Financial Statement Impact of Derivative Contracts
Realized loss	(6,508,000)	(48,093,000)	(33,560,000)
Unrealized gain (loss)	63,043,000	19,058,000	(20,372,000)
Total revenue: derivative gain (loss)	56,535,000	(29,035,000)	(53,932,000)
Amortization of premium payments	0	4,400,000	3,300,000
Derivative instruments not designated as hedging instruments | Derivative gain (loss) related to purchased product costs
Financial Statement Impact of Derivative Contracts
Realized loss	(26,493,000)	(27,711,000)	(21,909,000)
Unrealized gain (loss)	40,455,000	(25,249,000)	(5,804,000)
Total derivative gain (loss) related to purchase product costs	13,962,000	(52,960,000)	(27,713,000)
Derivative instruments not designated as hedging instruments | Derivative (loss ) gain related to facility expenses
Financial Statement Impact of Derivative Contracts
Unrealized gain (loss)	(1,371,000)	6,480,000	1,295,000
Derivative instruments not designated as hedging instruments | Derivative related to interest expense
Financial Statement Impact of Derivative Contracts
Realized loss			2,380,000
Unrealized gain (loss)			(509,000)
Derivative gain related to interest expense			1,871,000
Derivative instruments not designated as hedging instruments | Miscellaneous income, net
Financial Statement Impact of Derivative Contracts
Unrealized gain			$ 190,000