Investment Securities And Short-Term Investments (Summary Of Short-Term Investment Activity) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investment Securities And Short-Term Investments [Abstract]
Proceeds from sales and maturities of short-term investments	$ 34,150	$ 38,370	$ 67,685	$ 58,848
Purchases of short-term investments	$ 22,302	$ 50,249	$ 30,987	$ 63,647