Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Marketable securities - Short-Term
Gain (Loss) on Investments [Line Items]
Cost	$ 7,214	$ 8,063
Unrealized Gains	35	58
Unrealized Losses	0	0
Fair Value	7,249	8,121
Marketable securities - Short-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	3,332	4,817
Unrealized Gains	20	36
Unrealized Losses	0	0
Fair Value	3,352	4,853
Marketable securities - Short-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	3,882	3,113
Unrealized Gains	15	21
Unrealized Losses	0	0
Fair Value	3,897	3,134
Marketable securities - Short-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost		133
Unrealized Gains		1
Unrealized Losses		0
Fair Value		134
Marketable securities - Long-Term
Gain (Loss) on Investments [Line Items]
Cost	15,160	13,893
Unrealized Gains	82	172
Unrealized Losses	(12)	(13)
Fair Value	15,230	14,052
Marketable securities - Long-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	9,094	7,529
Unrealized Gains	30	66
Unrealized Losses	(10)	0
Fair Value	9,114	7,595
Marketable securities - Long-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	3,452	3,975
Unrealized Gains	27	61
Unrealized Losses	(1)	(1)
Fair Value	3,478	4,035
Marketable securities - Long-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	2,572	2,347
Unrealized Gains	25	45
Unrealized Losses	(1)	0
Fair Value	2,596	2,392
Marketable securities - Long-Term | Equity security
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	0	0
Unrealized Losses	0	(12)
Fair Value	$ 42	$ 30