Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Short-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	$ 5,797	$ 6,688
Unrealized Gains	3	0
Unrealized Losses	(29)	(18)
Fair Value	5,771	6,670
Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	10,332	9,077
Unrealized Gains	31	55
Unrealized Losses	(41)	(59)
Fair Value	10,322	9,073
U.S. Government And Agency Obligations [Member] | Short-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	3,377	4,381
Unrealized Gains	0	0
Unrealized Losses	(20)	(13)
Fair Value	3,357	4,368
U.S. Government And Agency Obligations [Member] | Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	6,114	4,801
Unrealized Gains	10	0
Unrealized Losses	(23)	(33)
Fair Value	6,101	4,768
Corporate Debt Securities And Certificates Of Deposit [Member] | Short-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	1,787	1,792
Unrealized Gains	3	0
Unrealized Losses	(5)	(4)
Fair Value	1,785	1,788
Corporate Debt Securities And Certificates Of Deposit [Member] | Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	754	1,189
Unrealized Gains	1	0
Unrealized Losses	(3)	(10)
Fair Value	752	1,179
Asset Backed Securities [Member] | Short-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	633	515
Unrealized Gains	0	0
Unrealized Losses	(4)	(1)
Fair Value	629	514
Asset Backed Securities [Member] | Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	3,422	3,045
Unrealized Gains	2	0
Unrealized Losses	(15)	(16)
Fair Value	3,409	3,029
Equity Security [Member] | Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	18	55
Unrealized Losses	0	0
Fair Value	$ 60	$ 97