Quarterly report pursuant to Section 13 or 15(d)

Organization And Accounting Policies (Rollforward Analysis Of The Allowance Against Accounts Receivable Balance) (Details)

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Organization And Accounting Policies (Rollforward Analysis Of The Allowance Against Accounts Receivable Balance) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Balance at beginning of year $ (2,535) $ (7,033)
Bad debt recovery 29 56
Adjustment associated with settlement of customs audit 623  
Foreign currency gain (loss) 29 (187)
Balance at end of period (1,854) (7,164)
Gabon    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Bad debt recovery $ 32 $ 100