Fair Value Measurments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Derivative Assets Abstract
Derivative assets	$ 230,385	$ 133,991
Long Term Derivative Assets	0	2,066
Derivative Liabilities Abstract
Derivative liabilities	0	718
Derivative Liabilities, Noncurrent	0	5,337
Fair Value Inputs Level 1 [Member]
Derivative Assets Abstract
Derivative assets	0
Long Term Derivative Assets	0
Fair Value Inputs Level 2 [Member]
Derivative Assets Abstract
Derivative assets	230,385
Long Term Derivative Assets	0
Fair Value Inputs Level 3 [Member]
Derivative Assets Abstract
Derivative assets	0
Long Term Derivative Assets	$ 0