Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Marketable securities - Short-Term
Gain (Loss) on Investments [Line Items]
Cost	$ 6,880	$ 8,063
Unrealized Gains	31	58
Unrealized Losses	0	0
Fair Value	6,911	8,121
Marketable securities - Short-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	3,278	4,817
Unrealized Gains	18	36
Unrealized Losses	0	0
Fair Value	3,296	4,853
Marketable securities - Short-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	3,475	3,113
Unrealized Gains	11	21
Unrealized Losses	0	0
Fair Value	3,486	3,134
Marketable securities - Short-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	127	133
Unrealized Gains	2	1
Unrealized Losses	0	0
Fair Value	129	134
Marketable securities - Long-Term
Gain (Loss) on Investments [Line Items]
Cost	15,549	13,893
Unrealized Gains	56	172
Unrealized Losses	(12)	(13)
Fair Value	15,593	14,052
Marketable securities - Long-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	9,077	7,529
Unrealized Gains	17	66
Unrealized Losses	(9)	0
Fair Value	9,085	7,595
Marketable securities - Long-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	3,755	3,975
Unrealized Gains	20	61
Unrealized Losses	(2)	(1)
Fair Value	3,773	4,035
Marketable securities - Long-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	2,675	2,347
Unrealized Gains	17	45
Unrealized Losses	(1)	0
Fair Value	2,691	2,392
Marketable securities - Long-Term | Equity security
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	2	0
Unrealized Losses	0	(12)
Fair Value	$ 44	$ 30