Derivative Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Crude oil	Sep. 30, 2011 Crude oil	Sep. 30, 2012 Crude oil	Sep. 30, 2011 Crude oil	Sep. 30, 2012 Natural gas	Sep. 30, 2011 Natural gas	Sep. 30, 2012 Natural gas	Sep. 30, 2011 Natural gas	Sep. 30, 2012 Natural gas liquids ("NGLs")	Sep. 30, 2011 Natural gas liquids ("NGLs")	Sep. 30, 2012 Natural gas liquids ("NGLs")	Sep. 30, 2011 Natural gas liquids ("NGLs")	Sep. 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	$ (10,921)	$ 3,755	$ (32,803)	$ 24,148	$ 2,472	$ 1,058	$ 13,142	$ 18,421	$ (9,031)	$ (1,434)	$ (40,495)	$ (3,751)	$ (4,362)	$ 4,131	$ (5,450)	$ 9,478
Unrealized (gain) loss on changes in fair value	(66,777)	132,180	7,237	108,020	(30,667)	106,780	32,616	90,629	(28,231)	19,083	(40,464)	21,504	(7,879)	6,317	15,085	(4,113)
Unrealized and Realized Derivative (Gain) Loss	55,856	(128,425)	(40,040)	(83,872)
Amount of (gain) loss reclassified from AOCL to realized hedge gain (loss)	(315)	4,271	(1,465)	9,149
Realized hedge gain (loss)	$ 501	$ (6,843)	$ 2,338	$ (14,548)
Interest rate on notes (as a percent)																	3.50%	3.50%