Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Marketable securities - Short-Term
Gain (Loss) on Investments [Line Items]
Cost	$ 8,626	$ 8,063
Unrealized Gains	54	58
Unrealized Losses	0	0
Fair Value	8,680	8,121
Marketable securities - Short-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	4,750	4,817
Unrealized Gains	30	36
Unrealized Losses	0	0
Fair Value	4,780	4,853
Marketable securities - Short-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	3,746	3,113
Unrealized Gains	24	21
Unrealized Losses	0	0
Fair Value	3,770	3,134
Marketable securities - Short-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	130	133
Unrealized Gains	0	1
Unrealized Losses	0	0
Fair Value	130	134
Marketable securities - Long-Term
Gain (Loss) on Investments [Line Items]
Cost	13,479	13,893
Unrealized Gains	115	172
Unrealized Losses	(7)	(13)
Fair Value	13,587	14,052
Marketable securities - Long-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	7,704	7,529
Unrealized Gains	42	66
Unrealized Losses	(5)	0
Fair Value	7,741	7,595
Marketable securities - Long-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	3,470	3,975
Unrealized Gains	34	61
Unrealized Losses	(2)	(1)
Fair Value	3,502	4,035
Marketable securities - Long-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	2,263	2,347
Unrealized Gains	34	45
Unrealized Losses	0	0
Fair Value	2,297	2,392
Marketable securities - Long-Term | Equity security
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	5	0
Unrealized Losses	0	(12)
Fair Value	$ 47	$ 30