Fair Value Measurements (Summary Of The Balances Company Has Elected To Account For At Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Other investments	$ 594,793	$ 549,805
Other assets	2,542	4,379
Other liabilities	$ 5,494	$ 17,383