Financial Instruments And Investments (Sale Of Securities And The Related Effects On Pre-Tax Income ) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Proceeds from sales of available-for-sale securities	$ 91,268	$ 102,567	$ 108,311
Gross realized gains included in pre-tax income	9,212	12,379	7,858
Gross realized losses included in pre-tax income	(1,220)	(927)	(508)
Gross unrealized losses included in pre-tax income	(352)	(338)	0
Net gains (losses) in pre-tax income	7,640	11,114	7,350
Net unrealized holding gains (losses) included in accumulated other comprehensive income	8,444	(2,906)	10,827
Net (gains) losses reclassified out of accumulated other comprehensive income	(7,640)	(11,114)	(7,350)
Net gains (losses) in other comprehensive income	$ 804	$ (14,020)	$ 3,477