Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Short-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	$ 7,307	$ 8,063
Unrealized Gains	22	58
Unrealized Losses	(2)	0
Fair Value	7,327	8,121
Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	17,343	13,893
Unrealized Gains	24	172
Unrealized Losses	(86)	(13)
Fair Value	17,281	14,052
U.S. Government And Agency Obligations [Member] | Short-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	3,005	4,817
Unrealized Gains	13	36
Unrealized Losses	0	0
Fair Value	3,018	4,853
U.S. Government And Agency Obligations [Member] | Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	9,921	7,529
Unrealized Gains	5	66
Unrealized Losses	(57)	0
Fair Value	9,869	7,595
Corporate Debt Securities And Certificates Of Deposit [Member] | Short-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	4,177	3,113
Unrealized Gains	8	21
Unrealized Losses	(2)	0
Fair Value	4,183	3,134
Corporate Debt Securities And Certificates Of Deposit [Member] | Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	4,869	3,975
Unrealized Gains	9	61
Unrealized Losses	(18)	(1)
Fair Value	4,860	4,035
Asset Backed Securities [Member] | Short-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	125	133
Unrealized Gains	1	1
Unrealized Losses	0	0
Fair Value	126	134
Asset Backed Securities [Member] | Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	2,511	2,347
Unrealized Gains	9	45
Unrealized Losses	(11)	0
Fair Value	2,509	2,392
Equity Security [Member] | Long-Term [Member]
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	1	0
Unrealized Losses	0	(12)
Fair Value	$ 43	$ 30