Derivative Instruments and Hedging Activities (Derivatives By Balance Sheet Location) (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Derivative financial instruments in Balance Sheet
Derivative Assets, Current	$ 57,764,000	$ 47,402,000
Derivative Assets, Noncurrent	36,672,000	29,000
Derivative Liabilities, Current	1,816,000	26,523,000
Derivative Liabilities, Noncurrent	0	18,872,000
Not Designated as Hedging Instrument [Member]
Derivative financial instruments in Balance Sheet
Derivative, Fair Value, Net	92,620,000	2,036,000
Oil contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative financial instruments in Balance Sheet
Derivative Assets, Current	44,550,000	23,452,000
Derivative Assets, Noncurrent	36,672,000	29,000
Derivative Liabilities, Current	(574,000)	(22,610,000)
Derivative Liabilities, Noncurrent	0	(18,702,000)
Natural Gas Contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative financial instruments in Balance Sheet
Derivative Assets, Current	13,214,000	23,950,000
Deferred Premiums [Member] | Not Designated as Hedging Instrument [Member]
Derivative financial instruments in Balance Sheet
Derivative Liabilities, Current	(1,242,000)	(3,913,000)
Derivative Liabilities, Noncurrent	$ 0	$ (170,000)