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Asset Retirements Obligations (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Notes To Financial Statements [Abstract]    
Carrying Amount at Beginning of Period $ 498,288 $ 456,484
Liabilities Incurred 68,703 39,480
Liabilities Settled (1) (66,129) (30,763)
Accretion 27,907 25,456
Revisions 58,786 1,640
Foreign Currency Translations (471) 5,991
Current Portion 29,527 32,005
Noncurrent Portion 557,557 466,283
Carrying Amount at End of Period $ 587,084 $ 498,288