Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Marketable securities - Short-Term
Gain (Loss) on Investments [Line Items]
Cost	$ 6,428	$ 6,688
Unrealized Gains	0	0
Unrealized Losses	(32)	(18)
Fair Value	6,396	6,670
Marketable securities - Short-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	3,611	4,381
Unrealized Gains	0	0
Unrealized Losses	(20)	(13)
Fair Value	3,591	4,368
Marketable securities - Short-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	2,163	1,792
Unrealized Gains	0	0
Unrealized Losses	(8)	(4)
Fair Value	2,155	1,788
Marketable securities - Short-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	654	515
Unrealized Gains	0	0
Unrealized Losses	(4)	(1)
Fair Value	650	514
Marketable securities - Long-Term
Gain (Loss) on Investments [Line Items]
Cost	9,855	9,077
Unrealized Gains	31	55
Unrealized Losses	(80)	(59)
Fair Value	9,806	9,073
Marketable securities - Long-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	6,399	4,801
Unrealized Gains	0	0
Unrealized Losses	(55)	(33)
Fair Value	6,344	4,768
Marketable securities - Long-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	230	1,189
Unrealized Gains	0	0
Unrealized Losses	(3)	(10)
Fair Value	227	1,179
Marketable securities - Long-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	3,184	3,045
Unrealized Gains	0	0
Unrealized Losses	(22)	(16)
Fair Value	3,162	3,029
Marketable securities - Long-Term | Equity security
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	31	55
Unrealized Losses	0	0
Fair Value	$ 73	$ 97