Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 7,701	$ 7,741
Gross unrealized gain	41	24
Gross unrealized loss	0	(9)
Fair value, investments	7,742	7,756
Less cash equivalents, Carrying amount	1,057	963	$ 840
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	667	568
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	667	568
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,656	7,687
Gross unrealized gain	41	24
Gross unrealized loss	0	0
Fair value, investments	7,697	7,711
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	45	54
Gross unrealized gain	0	0
Gross unrealized loss	0	(9)
Fair value, investments	45	45
Debt and Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	8,368	8,309
Gross unrealized gain	41	24
Gross unrealized loss	0	(9)
Fair value, investments	8,409	8,324
Less Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Less cash equivalents, Carrying amount	667	568
Less cash equivalents, Fair value	$ 667	$ 568