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Asset Retirement Obligations (Details) (USD $)
In Thousands
6 Months Ended
Jun. 30, 2011
Jun. 30, 2010
Notes To Financial Statements [Abstract]    
Carrying Amount at Beginning of Period $ 498,288 $ 456,484
Liabilities Incurred 12,973 10,601
Liabilities Settled (38,748) (8,168)
Accretion 12,268 12,086
Revisions 618 46
Foreign Currency Translations 2,834 (902)
Carrying Amount at End of Period 488,233 470,147
Current Portion 22,959 29,473
Noncurrent Portion $ 465,274 $ 440,674