Supplemental Cash Flow Information (Reconciliation of Cash, Cash Equivalents and Restricted Cash to Statement of Cash Flows) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	$ 326,558	$ 102,580	$ 126,619
Restricted cash	5,474	5,728	1,858
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 332,032	$ 108,308	$ 128,477	$ 54,948