Marketable Securities (Schedule Of Unrealized Loss Position) (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Fair Value
In Unrealized Loss Position For Less Than 12 Months	$ 833
In Unrealized Loss Position For Greater Than 12 Months	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(2)
In Unrealized Loss Position For Greater Than 12 Months	0
U.S. government and agency obligations [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months	149
In Unrealized Loss Position For Greater Than 12 Months	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(1)
In Unrealized Loss Position For Greater Than 12 Months	0
Asset backed securities [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months	684
In Unrealized Loss Position For Greater Than 12 Months	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(1)
In Unrealized Loss Position For Greater Than 12 Months	$ 0