Derivatives (Fair Value Of Derivative Instruments And Locations In Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Current derivative asset	$ 14,517	$ 31,938
Non-current derivative asset	1,948	4,514
Total derivatives designated as hedging instruments, assets	16,465	36,452
Total derivatives assets	16,465	36,452
Current portion of derivative liabilities	851	2,657
Non-current derivative liabilities	1,214	0
Total derivatives designated as hedging instruments, liabilities	2,065	2,657
Total derivative liabilities	2,065	2,657
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Current derivative asset	14,517	31,938
Non-current derivative asset	1,948	4,514
Current portion of derivative liabilities	851	2,657
Non-current derivative liabilities	$ 1,214	$ 0