Investments In Securities (Schedule Of Gross Realized Gains And Losses On Securities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Total, Gross realized gains	$ 164	$ 90
Total, Gross realized losses	(11)	0
Net realized gain from securities	153	90
Gain on other investments	0	13
Total	0	13
Net realized gain on investments	153	103
Issuer Obligations Of U S States Territories And Political Subdivisions Special Revenue [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Gross realized gains	0	0
Total, Gross realized losses	0	0
Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Total, Gross realized gains	0	0
Common Stocks And Nonredeemable Preferred Stocks
Schedule of Available-for-sale Securities [Line Items]
Total, Gross realized gains	164	90
Total, Gross realized losses	(11)	0
General Obligations Of U.S. States, Territories And Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Total, Gross realized losses	0	0
Impairments of Debt And Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Gross realized losses	$ 0	$ 0