Summary Of Significant Accounting Policies (Rollforward Analysis Of The Allowance Against Accounts Receivable Balance) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Bad Debt, Balance at January 1	$ (4,221)	$ (2,400)
Allowance for Bad Debt, Charged to costs and expenses	(1,222)	(2,699)	$ (2,400)
Allowance for Bad Debts, Foreign currency gain (loss)	232	878
Allowance for Bad Debt, Balance at December 31	(5,211)	(4,221)	(2,400)
Gabon [Member]
Allowance for Bad Debt, Charged to costs and expenses	$ (700)	$ (2,700)	$ (2,400)