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Asset Retirement Obligations (Details) (USD $)
In Thousands
9 Months Ended
Sep. 30, 2011
Sep. 30, 2010
Notes To Financial Statements [Abstract]  
Carrying Amount at Beginning of Period$ 498,288$ 456,484
Liabilities Incurred45,75427,439
Liabilities Settled(58,084)(21,653)
Accretion20,12519,105
Revisions61,66853,824
Foreign Currency Translations(3,688)1,980
Carrying Amount at End of Period564,063537,179
Current Portion30,30628,767
Noncurrent Portion$ 533,757$ 508,412