New Accounting Standards (Reconciliation Of Cash, Cash Equivalents, And Restricted Cash) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
New Accounting Standards [Abstract]
Cash and cash equivalents	$ 40,490	$ 19,669
Restricted cash - current	1,029	842
Restricted cash - non-current	918	967
Abandonment funding	10,808	10,808
Total cash, cash equivalents and restricted cash shown in the condensed consolidated statements of cash flows	$ 53,245	$ 32,286	$ 30,870	$ 30,643