Financial Instruments And Investments (Sale Of Securities And The Related Effects On Pre-Tax Income ) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment [Line Items]
Proceeds from sales of available-for-sale securities	$ 97,037	$ 91,268	$ 102,567
Gross realized gains included in pre-tax income	11,773	9,212	12,379
Gross realized losses included in pre-tax income	(1,147)	(1,220)	(927)
Gross unrealized losses included in pre-tax income	0	(352)	(338)
Net gains (losses) in pre-tax income	10,626	7,640	11,114
Net unrealized holding gains (losses) included in accumulated other comprehensive income	25,275	8,444	(2,906)
Net (gains) losses reclassified out of accumulated other comprehensive income	(10,626)	(7,640)	(11,114)
Net gains (losses) in other comprehensive income	$ 14,649	$ 804	$ (14,020)