Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Marketable securities - Short-Term
Gain (Loss) on Investments [Line Items]
Cost	$ 8,468	$ 8,268
Unrealized Gains	81	27
Unrealized Losses	0	0
Fair Value	8,549	8,295
Marketable securities - Short-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	4,927	5,766
Unrealized Gains	46	22
Unrealized Losses	0	0
Fair Value	4,973	5,788
Marketable securities - Short-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	3,408	1,085
Unrealized Gains	33	1
Unrealized Losses	0	0
Fair Value	3,441	1,086
Marketable securities - Short-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	133	1,417
Unrealized Gains	2	4
Unrealized Losses	0	0
Fair Value	135	1,421
Marketable securities - Long-Term
Gain (Loss) on Investments [Line Items]
Cost	13,513	12,105
Unrealized Gains	209	65
Unrealized Losses	(19)	(2)
Fair Value	13,703	12,168
Marketable securities - Long-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	7,268	6,524
Unrealized Gains	87	30
Unrealized Losses	(1)	(1)
Fair Value	7,354	6,553
Marketable securities - Long-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	3,732	3,004
Unrealized Gains	68	14
Unrealized Losses	(2)	0
Fair Value	3,798	3,018
Marketable securities - Long-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	2,471	2,535
Unrealized Gains	54	15
Unrealized Losses	0	(1)
Fair Value	2,525	2,549
Marketable securities - Long-Term | Equity security
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	0	6
Unrealized Losses	(16)	0
Fair Value	$ 26	$ 48