Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Marketable securities - Short-Term
Gain (Loss) on Investments [Line Items]
Cost	$ 8,234	$ 5,797
Unrealized Gains	19	3
Unrealized Losses	(8)	(29)
Fair Value	8,245	5,771
Marketable securities - Short-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	5,293	3,377
Unrealized Gains	14	0
Unrealized Losses	(6)	(20)
Fair Value	5,301	3,357
Marketable securities - Short-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	1,466	1,787
Unrealized Gains	2	3
Unrealized Losses	(1)	(5)
Fair Value	1,467	1,785
Marketable securities - Short-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	1,475	633
Unrealized Gains	3	0
Unrealized Losses	(1)	(4)
Fair Value	1,477	629
Marketable securities - Long-Term
Gain (Loss) on Investments [Line Items]
Cost	7,818	10,332
Unrealized Gains	78	31
Unrealized Losses	(3)	(41)
Fair Value	7,893	10,322
Marketable securities - Long-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	4,109	6,114
Unrealized Gains	38	10
Unrealized Losses	(1)	(23)
Fair Value	4,146	6,101
Marketable securities - Long-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	1,243	754
Unrealized Gains	8	1
Unrealized Losses	0	(3)
Fair Value	1,251	752
Marketable securities - Long-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	2,424	3,422
Unrealized Gains	20	2
Unrealized Losses	(2)	(15)
Fair Value	2,442	3,409
Marketable securities - Long-Term | Equity security
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	12	18
Unrealized Losses	0	0
Fair Value	$ 54	$ 60