Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Marketable securities - Short-Term
Gain (Loss) on Investments [Line Items]
Cost	$ 7,887	$ 8,268
Unrealized Gains	84	27
Unrealized Losses	0	0
Fair Value	7,971	8,295
Marketable securities - Short-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	5,789	5,766
Unrealized Gains	60	22
Unrealized Losses	0	0
Fair Value	5,849	5,788
Marketable securities - Short-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	1,578	1,085
Unrealized Gains	20	1
Unrealized Losses	0	0
Fair Value	1,598	1,086
Marketable securities - Short-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	520	1,417
Unrealized Gains	4	4
Unrealized Losses	0	0
Fair Value	524	1,421
Marketable securities - Long-Term
Gain (Loss) on Investments [Line Items]
Cost	14,250	12,105
Unrealized Gains	261	65
Unrealized Losses	(12)	(2)
Fair Value	14,499	12,168
Marketable securities - Long-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	6,807	6,524
Unrealized Gains	105	30
Unrealized Losses	0	(1)
Fair Value	6,912	6,553
Marketable securities - Long-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	4,831	3,004
Unrealized Gains	94	14
Unrealized Losses	0	0
Fair Value	4,925	3,018
Marketable securities - Long-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	2,570	2,535
Unrealized Gains	62	15
Unrealized Losses	0	(1)
Fair Value	2,632	2,549
Marketable securities - Long-Term | Equity security
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	0	6
Unrealized Losses	(12)	0
Fair Value	$ 30	$ 48