Financial Instruments And Investments (Sale Of Securities And The Related Effects On Pre-Tax Income ) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Proceeds from sales or maturities of available-for-sale securities	$ 168,177	$ 25,955	$ 97,037
Gross realized gains included in pre-tax income	4,815	17	11,773
Gross realized losses included in pre-tax income	(2,583)	(1,462)	(1,147)
Debt Securities, Realized Gain (Loss)	$ 2,232	$ (1,445)	$ 10,626