Marketable Securities (Schedule Of Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value
In Unrealized Loss Position For Less Than 12 Months	$ 7,590	$ 741
In Unrealized Loss Position For Greater Than 12 Months	0	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(12)	(1)
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	5,365	330
In Unrealized Loss Position For Greater Than 12 Months	0	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(10)	0
In Unrealized Loss Position For Greater Than 12 Months	0	0
Corporate Debt Securities And Certificates Of Deposit [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months	1,676	411
In Unrealized Loss Position For Greater Than 12 Months	0	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(1)	(1)
In Unrealized Loss Position For Greater Than 12 Months	0	$ 0
Asset backed securities [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months	549
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