Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Marketable securities - Short-Term
Gain (Loss) on Investments [Line Items]
Cost	$ 6,708	$ 6,490
Unrealized Gains	0	5
Unrealized Losses	(7)	(2)
Fair Value	6,701	6,493
Marketable securities - Short-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	4,693	5,005
Unrealized Gains	0	4
Unrealized Losses	(6)	(1)
Fair Value	4,687	5,008
Marketable securities - Short-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	1,665	1,476
Unrealized Gains	0	1
Unrealized Losses	(1)	(1)
Fair Value	1,664	1,476
Marketable securities - Short-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	350	9
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	350	9
Marketable securities - Long-Term
Gain (Loss) on Investments [Line Items]
Cost	8,930	8,750
Unrealized Gains	43	12
Unrealized Losses	(24)	(34)
Fair Value	8,949	8,728
Marketable securities - Long-Term | U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Cost	4,525	4,815
Unrealized Gains	0	1
Unrealized Losses	(13)	(12)
Fair Value	4,512	4,804
Marketable securities - Long-Term | Corporate debt securities and certificates of deposit
Gain (Loss) on Investments [Line Items]
Cost	1,566	2,161
Unrealized Gains	1	0
Unrealized Losses	(6)	(17)
Fair Value	1,561	2,144
Marketable securities - Long-Term | Asset backed securities
Gain (Loss) on Investments [Line Items]
Cost	2,797	1,732
Unrealized Gains	0	0
Unrealized Losses	(5)	(5)
Fair Value	2,792	1,727
Marketable securities - Long-Term | Equity security
Gain (Loss) on Investments [Line Items]
Cost	42	42
Unrealized Gains	42	11
Unrealized Losses	0	0
Fair Value	$ 84	$ 53