Organization and Accounting Policies (Reconciliation of Cash, Cash Equivalents, and Restricted Cash) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Organization and Accounting Policies [Abstract]
Cash and cash equivalents	$ 44,841	$ 45,917	$ 48,557
Restricted cash - current	1,090	911	799
Restricted cash - non-current	925	925	922
Abandonment funding	11,420	11,371	11,550
Total cash, cash equivalents and restricted cash	$ 58,276	$ 59,124	$ 61,828	$ 46,655