Summary of Significant Accounting Policies (Reconciliation of Cash, Cash Equivalents, and Restricted Cash) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 451,071	$ 371,341
Restricted cash and cash equivalents included in other current assets	7,224	4,423
Restricted cash and cash equivalents included in other assets	2,461	3,712
Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows	$ 460,756	$ 379,476	$ 327,418	$ 591,729