Marketable Securities (Schedule Of Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value
In Unrealized Loss Position For Less Than 12 Months	$ 3,185	$ 833
In Unrealized Loss Position For Greater Than 12 Months	0	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(18)	(2)
In Unrealized Loss Position For Greater Than 12 Months	0	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
Corporate Debt Securities And Certificates Of Deposit [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months	2,045
In Unrealized Loss Position For Greater Than 12 Months	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(13)
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	1,140	684
In Unrealized Loss Position For Greater Than 12 Months	0	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(5)	(1)
In Unrealized Loss Position For Greater Than 12 Months	$ 0	$ 0