Derivative Instruments and Hedging Activities (Impact of Derivative Instruments on Accumulated Comprehensive Income (Loss)) (Details) (USD $) In Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ 20,970	[1]	$ 2,063	[1]	$ 10,403	[1]	$ 16,103	[1]
Oil and Natural Gas Commodity Contract [Member]
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	20,720	[1]	2,575	[1]	9,942	[1]	17,205	[1]
Interest Rate Swap [Member]
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ 250	[1]	$ (512)	[1]	$ 461	[1]	$ (1,102)	[1]

[1] All unrealized gains (losses) related to our derivatives are expected to be reclassified into earnings by no later than December 31, 2012. The last of our interest swaps will mature in January 2012 and we have foreign exchange forwards and oil and natural gas commodity contracts that have maturities through June and December 2012, respectively.