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Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 7,725	$ 7,741
Gross unrealized gain	33	24
Gross unrealized loss	(9)	(9)
Fair value, investments	7,749	7,756
Cash equivalents, Carrying amount	853	963	$ 1,185	$ 840
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	316	568
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	316	568
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,671	7,687
Gross unrealized gain	33	24
Gross unrealized loss	0	0
Fair value, investments	7,704	7,711
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	54	54
Gross unrealized gain	0	0
Gross unrealized loss	(9)	(9)
Fair value, investments	45	45
Debt and Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	8,041	8,309
Gross unrealized gain	33	24
Gross unrealized loss	(9)	(9)
Fair value, investments	8,065	8,324
Less Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Cash equivalents, Carrying amount	316	568
Cash equivalents, Fair value	$ 316	$ 568