Marketable Securities (Schedule Of Schedule of Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Marketable securities - Short-Term [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months	$ 7,911
In Unrealized Loss Position For Greater Than 12 Months	6,579
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(70)
In Unrealized Loss Position For Greater Than 12 Months	(47)
Marketable securities - Short-Term [Member] | U.S. government and agency obligations [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months	5,190
In Unrealized Loss Position For Greater Than 12 Months	3,488
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(49)
In Unrealized Loss Position For Greater Than 12 Months	(21)
Marketable securities - Short-Term [Member] | Corporate Debt Securities And Certificates Of Deposit [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months	227
In Unrealized Loss Position For Greater Than 12 Months	1,721
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(3)
In Unrealized Loss Position For Greater Than 12 Months	(13)
Marketable securities - Short-Term [Member] | Asset backed securities [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months	2,494
In Unrealized Loss Position For Greater Than 12 Months	1,370
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months	(18)
In Unrealized Loss Position For Greater Than 12 Months	$ (13)
Marketable securities - Long-Term [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months		$ 8,383
In Unrealized Loss Position For Greater Than 12 Months		6,766
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months		(40)
In Unrealized Loss Position For Greater Than 12 Months		(37)
Marketable securities - Long-Term [Member] | U.S. government and agency obligations [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months		5,593
In Unrealized Loss Position For Greater Than 12 Months		3,543
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months		(29)
In Unrealized Loss Position For Greater Than 12 Months		(17)
Marketable securities - Long-Term [Member] | Corporate Debt Securities And Certificates Of Deposit [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months		478
In Unrealized Loss Position For Greater Than 12 Months		1,991
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months		(2)
In Unrealized Loss Position For Greater Than 12 Months		(12)
Marketable securities - Long-Term [Member] | Asset backed securities [Member]
Fair Value
In Unrealized Loss Position For Less Than 12 Months		2,312
In Unrealized Loss Position For Greater Than 12 Months		1,232
Gross Unrealized Losses
In Unrealized Loss Position For Less Than 12 Months		(9)
In Unrealized Loss Position For Greater Than 12 Months		$ (8)