Summary of Significant Accounting Policies (Components of Cash, cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 371,341	$ 584,581	$ 301,353
Restricted cash and cash equivalents included in other current assets	4,423	2,697	9,081
Restricted cash and cash equivalents included in other assets	3,712	4,451	503
Total cash, cash equivalents, and restricted cash shown in the consolidated statement of cash flows	$ 379,476	$ 591,729	$ 310,937	$ 398,578