Summary of Significant Accounting Policies (Reconciliation of Cash, Cash Equivalents, and Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary Of Significant Accounting Policies [Abstract]
Cash and cash equivalents	$ 45,917	$ 33,360
Restricted cash - current	911	804
Restricted cash - non-current	925	920
Abandonment funding	11,371	11,571
Total cash, cash equivalents and restricted cash	$ 59,124	$ 46,655	$ 32,286	$ 30,643