Supplemental Cash Flow Information (Reconciliation of Cash, Cash Equivalents and Restricted Cash to Statement of Cash Flows) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	$ 281,849	$ 102,580	$ 67,165
Restricted cash	5,434	5,728	1,732
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 287,283	$ 108,308	$ 68,897	$ 54,948