Summary of Significant Accounting Policies (Reconciliation of Cash, Cash Equivalents, and Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies [Abstract]
Cash and cash equivalents	$ 48,675	$ 47,853
Restricted cash - current	79	86
Restricted cash - non-current	1,752	925
Abandonment funding	21,808	12,453
Total cash, cash equivalents and restricted cash	$ 72,314	$ 61,317	$ 59,124	$ 46,655