Derivative Instruments and Hedging Activities (Derivatives By Balance Sheet Location) (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Derivative financial instruments in Balance Sheet
Derivative Assets, Current	$ 16,820,000	$ 47,402,000
Derivative Assets, Noncurrent	12,820,000	29,000
Derivative Liabilities, Current	2,395,000	26,523,000
Derivative Liabilities, Noncurrent	1,999,000	18,872,000
Not Designated as Hedging Instrument [Member]
Derivative financial instruments in Balance Sheet
Derivative, Fair Value, Net	25,246,000	2,036,000
Crude Oil Contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative financial instruments in Balance Sheet
Derivative Assets, Current	10,780,000	23,452,000
Derivative Assets, Noncurrent	12,820,000	29,000
Derivative Liabilities, Current	(1,680,000)	(22,610,000)
Derivative Liabilities, Noncurrent	(1,999,000)	(18,702,000)
Natural Gas Contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative financial instruments in Balance Sheet
Derivative Assets, Current	6,040,000	23,950,000
Deferred Premiums [Member] | Not Designated as Hedging Instrument [Member]
Derivative financial instruments in Balance Sheet
Derivative Liabilities, Current	(715,000)	(3,913,000)
Derivative Liabilities, Noncurrent	$ 0	$ (170,000)