Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Marketable securities - Short-Term
Gain (Loss) on Investments [Line Items]
Cost	$ 7,777	$ 5,797
Unrealized Gains	17	3
Unrealized Losses	(2)	(29)
Fair Value	7,792	5,771
Marketable securities - Short-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	5,138	3,377
Unrealized Gains	11	0
Unrealized Losses	(2)	(20)
Fair Value	5,147	3,357
Marketable securities - Short-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	1,170	1,787
Unrealized Gains	1	3
Unrealized Losses	0	(5)
Fair Value	1,171	1,785
Marketable securities - Short-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	1,469	633
Unrealized Gains	5	0
Unrealized Losses	0	(4)
Fair Value	1,474	629
Marketable securities - Long-Term
Gain (Loss) on Investments [Line Items]
Cost	9,325	10,332
Unrealized Gains	68	31
Unrealized Losses	(1)	(41)
Fair Value	9,392	10,322
Marketable securities - Long-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	5,646	6,114
Unrealized Gains	32	10
Unrealized Losses	(1)	(23)
Fair Value	5,677	6,101
Marketable securities - Long-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	1,602	754
Unrealized Gains	12	1
Unrealized Losses	0	(3)
Fair Value	1,614	752
Marketable securities - Long-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	2,035	3,422
Unrealized Gains	17	2
Unrealized Losses	0	(15)
Fair Value	2,052	3,409
Marketable securities - Long-Term | Equity security
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	7	18
Unrealized Losses	0	0
Fair Value	$ 49	$ 60