Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 8,052	$ 54
Gross unrealized gain	1	0
Gross unrealized loss	(12)	(9)
Fair value, investments	8,041	45
Less cash equivalents, Carrying amount	1,090	8,785	$ 1,057
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	718	797
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	718	797
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,998	7,734
Gross unrealized gain	1	0
Gross unrealized loss	0	0
Fair value, investments	7,999	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	8,770	8,585
Gross unrealized gain	1	0
Gross unrealized loss	(12)	(9)
Fair value, investments	8,759	8,576
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	718	8,531
Less cash equivalents, Fair value	$ 718	$ 8,531