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Commitments And Contingencies - Narrative (Details) (Collectibility of Receivables [Member], Angola Customer [Member], USD $)
12 Months Ended
Dec. 31, 2011
Mar. 31, 2012
Collectibility of Receivables [Member] | Angola Customer [Member]
   
Loss Contingencies [Line Items]    
Accounts receivable, overdue $ 40,000,000 $ 40,000,000
Sales Returns and Allowances, Goods (3,000,000)  
Account Receivable Present Value Estimate Reclassified to Non-current Asset $ 22,000,000 $ 22,000,000