Nature of Ops and Sign. Acctg Policies (Cash, Cash Equivalents, and Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 18, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 518		$ 516
Restricted cash, current	1,000		0
Restricted cash included in other assets	40,730		32,529
Total cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$ 42,248	$ 95,114	$ 33,045	$ 54,949	$ 15,992