Derivative Financial Instruments (Details 2) (Derivatives not designated as hedging instruments, USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Current Assets
Fair value of derivative assets and liabilities
Derivative Instruments, Assets	$ 69,207		$ 55,813
Noncurrent Assets
Fair value of derivative assets and liabilities
Derivative Instruments, Assets	44,270		31,062
Current Liabilities
Fair value of derivative assets and liabilities
Derivative Instruments, Liabilities	9,150		42,806
Noncurrent liabilities
Fair value of derivative assets and liabilities
Derivative Instruments, Liabilities	956		12,875
Level 2 | Fair Value, Measurements, Recurring [Member]
Fair value of derivative assets and liabilities
Fair value: Derivative Assets	113,477	[1]	86,875	[1]
Fair value: Derivative Liabilities	$ 10,106	[1]	$ 55,681	[1]

[1] This represents a financial asset or liability that is measured at fair value on a recurring basis.