Derivatives And Fair Value Measurements (Estimated Fair Value Of Derivative Instruments Under Input Levels) (Details) (USD $) In Thousands	Sep. 30, 2010	Jun. 30, 2010	Dec. 31, 2009	Sep. 30, 2011 Asset Derivatives [Member]	Dec. 31, 2010 Asset Derivatives [Member]	Sep. 30, 2011 Asset Derivatives [Member] Fair Value, Inputs, Level 2 [Member] Commodity Contracts [Member]	Dec. 31, 2010 Asset Derivatives [Member] Fair Value, Inputs, Level 2 [Member] Commodity Contracts [Member]	Sep. 30, 2011 Asset Derivatives [Member] Fair Value, Inputs, Level 3 [Member] Commodity Contracts [Member]	Dec. 31, 2010 Asset Derivatives [Member] Fair Value, Inputs, Level 3 [Member] Commodity Contracts [Member]	Sep. 30, 2011 Liability Derivatives [Member]	Dec. 31, 2010 Liability Derivatives [Member]	Sep. 30, 2011 Liability Derivatives [Member] Fair Value, Inputs, Level 2 [Member] Commodity Contracts [Member]	Dec. 31, 2010 Liability Derivatives [Member] Fair Value, Inputs, Level 2 [Member] Commodity Contracts [Member]	Dec. 31, 2010 Liability Derivatives [Member] Fair Value, Inputs, Level 3 [Member] Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Estimated fair value of derivative instruments	$ 226,594	$ 200,473	$ 105,364	$ 207,850	$ 146,762	$ 140,740	$ 146,762	$ 67,110		$ 1,677		$ 1,677