Summary Of Business And Significant Accounting Policies (Reconciliation of Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents, unrestricted	$ 898,426	$ 779,345
Cash and cash equivalents, restricted	333	332
Total unrestricted and restricted cash and cash equivalents	$ 898,759	$ 779,677	$ 672,941	$ 501,250