Marketable Securities (Schedule Of Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value
In Unrealized Loss Position For Less Than 12 Months	$ 7,456	$ 741
In Unrealized Loss Position For Greater Than 12 Months	226	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(11)	(1)
In Unrealized Loss Position For Greater Than 12 Months	(1)	0
U.S. government and agency obligations
Fair Value
In Unrealized Loss Position For Less Than 12 Months	5,275	330
In Unrealized Loss Position For Greater Than 12 Months	0	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(9)	0
In Unrealized Loss Position For Greater Than 12 Months	0	0
Corporate debt securities and certificates of deposit
Fair Value
In Unrealized Loss Position For Less Than 12 Months	1,247	411
In Unrealized Loss Position For Greater Than 12 Months	226	0
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(1)	(1)
In Unrealized Loss Position For Greater Than 12 Months	(1)	$ 0
Asset backed securities
Fair Value
In Unrealized Loss Position For Less Than 12 Months	934
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