Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 2,052	$ 54
Gross unrealized gain	1	0
Gross unrealized loss	(12)	(9)
Fair value, investments	2,041	45
Cash equivalents, Carrying amount	7,062	8,785	$ 3,117	$ 1,057
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	866	797
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	866	797
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,748	7,734
Gross unrealized gain	1	0
Gross unrealized loss	0	0
Fair value, investments	7,749	7,734
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	54	54
Gross unrealized gain	0	0
Gross unrealized loss	(12)	(9)
Fair value, investments	42	45
Debt and Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	8,668	8,585
Gross unrealized gain	1	0
Gross unrealized loss	(12)	(9)
Fair value, investments	8,657	8,576
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	6,616	8,531
Cash equivalents, Fair value	$ 6,616	$ 8,531