Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Marketable securities - Short-Term
Gain (Loss) on Investments [Line Items]
Cost	$ 7,531	$ 8,268
Unrealized Gains	63	27
Unrealized Losses	(1)	0
Fair Value	7,593	8,295
Marketable securities - Short-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	5,386	5,766
Unrealized Gains	60	22
Unrealized Losses	0	0
Fair Value	5,446	5,788
Marketable securities - Short-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	1,170	1,085
Unrealized Gains	2	1
Unrealized Losses	(1)	0
Fair Value	1,171	1,086
Marketable securities - Short-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	975	1,417
Unrealized Gains	1	4
Unrealized Losses	0	0
Fair Value	976	1,421
Marketable securities - Long-Term
Gain (Loss) on Investments [Line Items]
Cost	15,037	12,105
Unrealized Gains	179	65
Unrealized Losses	(29)	(2)
Fair Value	15,187	12,168
Marketable securities - Long-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	7,349	6,524
Unrealized Gains	141	30
Unrealized Losses	0	(1)
Fair Value	7,490	6,553
Marketable securities - Long-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	4,760	3,004
Unrealized Gains	21	14
Unrealized Losses	(12)	0
Fair Value	4,769	3,018
Marketable securities - Long-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	2,886	2,535
Unrealized Gains	17	15
Unrealized Losses	(5)	(1)
Fair Value	2,898	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