Derivative Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Crude oil	Jun. 30, 2011 Crude oil	Jun. 30, 2012 Crude oil	Jun. 30, 2011 Crude oil	Jun. 30, 2012 Natural gas	Jun. 30, 2011 Natural gas	Jun. 30, 2012 Natural gas	Jun. 30, 2011 Natural gas	Jun. 30, 2012 Natural gas liquids ("NGLs")	Jun. 30, 2011 Natural gas liquids ("NGLs")	Jun. 30, 2012 Natural gas liquids ("NGLs")	Jun. 30, 2011 Natural gas liquids ("NGLs")	Jun. 30, 2012 Convertible Debt [Member]	Dec. 31, 2011 Convertible Debt [Member]
Unrealized and realized gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Cash settlement (gain) and loss	$ (16,446)	$ 13,976	$ (21,882)	$ 20,393	$ 2,371	$ 10,633	$ 10,670	$ 17,363	$ (16,252)	$ (590)	$ (31,464)	$ (2,317)	$ (2,565)	$ 3,933	$ (1,088)	$ 5,347
Unrealized (gain) loss on changes in fair value	81,666	57,852	74,014	(24,160)	92,774	51,216	63,283	(16,151)	(29,867)	6,681	(12,233)	2,421	18,759	(45)	22,964	(10,430)
Unrealized and Realized Derivative (Gain) Loss	(98,112)	(43,876)	(95,896)	44,553
Amount of (gain) loss reclassified from AOCL to realized hedge gain (loss)	(116)	3,951	(1,150)	4,878
Realized hedge gain (loss)	$ 185	$ (6,330)	$ 1,837	$ (7,705)
Interest rate on notes (as a percent)																	3.50%	3.50%