Accrued Liabilities and Other (Schedule of Accrued Liabilities and Other Balances) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accrued Liabilities and Other [Abstract]
Accrued accounts payable invoices	$ 4,070	$ 4,650
Joint venture audit settlement		3,322
Gabon DMO, PID and PIH obligations	3,960	3,314
Capital expenditures	435	11,792
Stock appreciation rights - current portion	2,289	2,638
Accrued wages and other compensation	2,108	1,731
Other	4,322	2,326
Total accrued liabilities and other	$ 17,184	$ 29,773