Summary Of Significant Accounting Policies (Summary Of Cash And Cash Equivalents) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Cash accounts	$ 427,244	$ 506,731
Money market mutual funds	356,924	281,333
Cash and cash equivalents	$ 784,168	$ 788,064	$ 742,486	$ 576,703
Cash accounts, % of Total	54.50%	64.30%
Money market mutual funds, % of Total	45.50%	35.70%