Derivative Financial Instruments (Derivative Instruments) (Details) (Not Designated As Hedging Instruments [Member], USD $) In Thousands	Jun. 30, 2011		Dec. 31, 2010
Total derivatives, Asset	$ 319,862	[1]	$ 347,802	[1]
Total derivatives, Liability	207,455	[1]	162,683	[1]
Interest Rate Derivatives [Member] | Derivatives - Current [Member]
Total derivatives, Asset	12,253	[1]	11,903	[1]
Total derivatives, Liability			886	[1]
Interest Rate Derivatives [Member] | Derivatives - Noncurrent [Member]
Total derivatives, Asset	17,870	[1]	15,762	[1]
Total derivatives, Liability	5,177	[1]	9,227	[1]
Commodity Price Derivatives [Member] | Derivatives - Current [Member]
Total derivatives, Asset	153,812	[1]	167,406	[1]
Total derivatives, Liability	87,944	[1]	87,741	[1]
Commodity Price Derivatives [Member] | Derivatives - Noncurrent [Member]
Total derivatives, Asset	135,927	[1]	152,731	[1]
Total derivatives, Liability	$ 114,334	[1]	$ 64,829	[1]

[1] Derivative assets and liabilities shown in the tables above are presented as gross assets and liabilities, without regard to master netting arrangements which are considered in the presentations of derivative assets and liabilities in the accompanying consolidated balance sheets.